Camel milk: A review of its nutritional value, heat stability, and potential food products.

✅ 全文

骆驼奶：营养价值、热稳定性及潜在食品产品的综述

作者 Ho Thao M; Zou Zhengzheng; Bansal Nidhi 期刊 Food Research International (Ottawa, Ont.) 发表日期 2022 卷/期/页码 Vol. 153 ISSN 1873-7145 DOI 10.1016/j.foodres.2021.110870 类型原创研究 (Original Research)

📄 中文摘要 Chinese Abstract

中文

骆驼奶（CM）相较于牛乳具有更优的营养价值，且其成分与母乳高度相似，因此被视为一种极具潜力的替代品，尤其在母乳获取困难的地区。骆驼奶富含免疫球蛋白、乳铁蛋白、溶菌酶和乳过氧化物酶等生物活性化合物，赋予其抗癌、抗糖尿病和抗菌等特性。尽管具备这些优势，骆驼奶的全球利用率仍然较低，以其为原料的食品也较为稀缺，原因在于其成分与牛乳存在差异——尤其是κ-酪蛋白含量较低且缺乏β-乳球蛋白——这影响了其热稳定性并制约了产品开发。

📋 英文结构化总结 English Structured Summary

全文整理

Background:

Camel milk (CM) is recognized for its superior nutritional value compared to bovine milk and its close resemblance to human milk, making it a promising alternative, especially in regions where human milk is inaccessible. It contains high levels of bioactive compounds such as immunoglobulins, lactoferrin, lysozyme, and lactoperoxidase, which contribute to anti-cancer, anti-diabetic, and anti-bacterial properties. Despite these benefits, the global utilization of CM remains limited, and food products derived from it are scarce due to challenges in processing caused by differences in composition from bovine milk—particularly lower kappa-casein content and the absence of β-lactoglobulin—which affect heat stability and product development.

Methods:

This is a review article; therefore, no original experimental methods were employed. The authors conducted a comprehensive literature analysis focusing on the composition, bioactive compounds, heat stability, and potential food applications of camel milk. Data were synthesized from existing studies on CM’s macro-nutrients, biological functionalities (e.g., hypoglycaemic, antimicrobial, immunological effects), responses to thermal processing, and technological aspects of producing various CM-based products such as pasteurized milk, powder, ice cream, cheese, butter, and yoghurt. Technical challenges and research gaps in CM processing were also identified and discussed.

Results:

Camel milk exhibits unique compositional traits: it has a high proportion of β-casein (65% of total caseins), lacks allergenic β-lactoglobulin, and contains elevated levels of α-lactalbumin and lactoferrin—similar to human milk. Its fat globules are smaller than those in bovine milk, enhancing digestibility. CM demonstrates significant bioactivities, including hypoglycaemic effects (reducing insulin needs in type 1 diabetes patients by 30%), antimicrobial action against pathogens like *E. coli* and *S. aureus*, and hypoallergenic properties suitable for children with bovine milk allergy. However, CM shows poor heat stability at high temperatures (e.g., heat coagulation time <3 min at 130°C), limiting sterilization efforts. While CM whey proteins are generally more heat-resistant than bovine counterparts, key bioactive proteins like lactoferrin and GlyCAM-1 suffer substantial losses during pasteurization (25–85%) and spray drying (85–95%).

Data Summary:

Quantitative findings include: CM protein content ranges from 3.10% to 3.36% (w/v) across regions; fat content varies between 3.31% and 4.14%; lactose averages ~4.45%; and ash content is ~0.77%. Vitamin C levels are 3–5 times higher than in bovine milk. Heat coagulation time at 140°C is only 133.6 seconds for CM versus 1807.4 seconds for bovine milk. During spray drying, camel serum albumin decreases by ~14%, while α-lactalbumin remains relatively stable (~3.3% loss). Solubility of spray-dried CM powder is high initially (98.62%) but declines slightly during storage due to surface lipid accumulation.

Conclusions:

Camel milk holds strong potential as a functional food and alternative to bovine and human milk, particularly for individuals with allergies or metabolic disorders. However, its poor heat stability at high temperatures poses major technological barriers to producing sterilized or UHT-treated liquid products. Although freeze drying preserves bioactive compounds effectively, it is costly and impractical for large-scale use. Spray drying shows promise but requires optimization to minimize protein denaturation. Current commercial CM products are mostly pasteurized or reconstituted from powder, with limited variety compared to bovine milk. Further research is needed to stabilize CM during thermal processing and expand its product portfolio.

Practical Significance:

The insights from this review can guide dairy technologists and food manufacturers in developing improved processing techniques for camel milk, enabling broader commercialization. Potential applications include hypoallergenic infant formulas, functional beverages, specialty dairy products (e.g., ice cream, cheese), and nutraceuticals targeting diabetes and immune support. Overcoming heat instability through pH adjustment, additives, or novel non-thermal methods (e.g., high-pressure processing) could unlock new markets, especially in arid regions where camels are prevalent and conventional dairy farming is challenging.

📋 中文结构化总结 Chinese Structured Summary

中文

背景:

方法:

本文为综述类文章，未采用原创性实验方法。作者围绕骆驼奶的成分组成、生物活性化合物、热稳定性及潜在食品应用进行了全面的文献分析。数据综合自现有关于骆驼奶宏量营养素、生物功能特性（如降血糖、抗菌和免疫学效应）、热加工响应以及各类骆驼奶基产品（如巴氏杀菌乳、奶粉、冰淇淋、奶酪、黄油和酸奶）生产技术的研究。同时，本文还识别并讨论了骆驼奶加工中的技术挑战和研究空白。

结果:

骆驼奶具有独特的成分特征：β-酪蛋白占总酪蛋白的比例高达65%，不含致敏性β-乳球蛋白，且α-乳白蛋白和乳铁蛋白含量较高——与母乳相似。其脂肪球小于牛乳，有助于提高消化率。骆驼奶表现出显著的生物活性，包括降血糖效应（可使1型糖尿病患者的胰岛素需求量降低30%）、对大肠杆菌和金黄色葡萄球菌等病原体的抗菌作用，以及适用于牛乳过敏儿童的低致敏特性。然而，骆驼奶在高温下热稳定性较差（如在130°C下热凝固时间<3分钟），限制了灭菌处理。尽管骆驼奶乳清蛋白总体上比牛乳对应蛋白更耐热，但乳铁蛋白和GlyCAM-1等关键生物活性蛋白在巴氏杀菌过程中损失显著（25%–85%），喷雾干燥过程中损失更为严重（85%–95%）。

数据汇总:

定量研究结果显示：各地区骆驼奶蛋白质含量范围为3.10%–3.36%（w/v）；脂肪含量在3.31%–4.14%之间；乳糖平均含量约为4.45%；灰分含量约为0.77%。维生素C含量为牛乳的3–5倍。在140°C条件下，骆驼奶的热凝固时间仅为133.6秒，而牛乳为1807.4秒。喷雾干燥过程中，骆驼血清白蛋白减少约14%，而α-乳白蛋白相对稳定（损失约3.3%）。喷雾干燥骆驼奶粉初始溶解度较高（98.62%），但在储存期间因表面脂质积累而略有下降。

结论:

骆驼奶作为功能性食品及牛乳和母乳的替代品具有巨大潜力，尤其适用于过敏或代谢紊乱人群。然而，其在高温下的较差热稳定性对生产灭菌或超高温瞬时处理液态产品构成了重大技术障碍。虽然冷冻干燥能有效保留生物活性化合物，但成本高昂且难以大规模应用。喷雾干燥前景良好，但需进一步优化以减少蛋白质变性。目前商业化骆驼奶产品多为巴氏杀菌乳或奶粉复原产品，品种远不及牛乳丰富。未来研究需着力解决骆驼奶在热加工过程中的稳定性问题，并拓展其产品品类。

实践意义:

本综述的见解可为乳制品技术人员和食品制造商提供参考，助力开发改进型骆驼奶加工技术，推动其更广泛的商业化应用。潜在应用方向包括低致敏婴儿配方奶粉、功能性饮料、特色乳制品（如冰淇淋、奶酪）以及针对糖尿病和免疫支持的营养保健品。通过pH调节、添加辅料或新型非热处理技术（如高压处理）克服热不稳定性问题，有望开辟新市场，尤其是在骆驼资源丰富而传统畜牧业面临挑战的干旱地区。

📖 英文全文 English Full Text

Food Research International 153 (2022) 110870 Available online 7 December 2021

Review Camel milk: A review of its nutritional value, heat stability, and potential food products

Thao M. Ho a,b,*, Zhengzheng Zou b, Nidhi Bansal b,* a Department of Food and Nutrition, University of Helsinki, P.O. Box 66, 00014, Finland b School of Agriculture and Food Sciences, University of Queensland, Brisbane, QLD 4072, Australia

A R T I C L E I N F O Keywords:

Camel milk Heat treatment Bioactive compounds Camel milk products

A B S T R A C T Camel milk is superior to bovine milk and quite close to human milk in terms of its nutritional value. It contains high concentrations of many bioactive compounds that are essential for human health. Despite its profound nutritional and health benefits, food products produced from camel milk are still very limited compared to bovine milk. Differences in the composition of bovine and camel milk make the production processes for bovine milk products unsuitable for camel milk products. Therefore, a comprehensive understanding regarding the composition, bioactive compounds, and the heat stability of camel milk is essential to preserve the inherent nutritional value of camel milk while achieving desirable attributes in the final products. In this review, the properties and functionalities of macro-nutrients in camel milk, especially heat stability of camel milk and its proteins are described. In addition, technical aspects of the production of various camel milk products, including difficulties in their production and directions for further research to enhance their quality, are comprehensively discussed.

1. Introduction A hot climate, scarce water reserves, and lack of pastures are preferred environmental conditions for camels. Therefore, camels are typically raised in countries with large desert areas, and they can be used for many purposes such as milk, meat, wool, transport, race, tourism, agricultural work, and cosmetics (Faye, 2015; Saalfeld & Edwards,

2010). In terms of milk production, according to FAO (2019), African countries (e.g. Somalia, Sudan, Nigeria, Kenya, Chad, Mauritania,

Ethiopia, and Mali) account for approximately 90% of the fresh whole camel milk (CM) global production, followed by Asian countries (e.g.

India, Yemen, Saudi Arabia, United Arab Emirates, China, and

Afghanistan). Camel milk has nutritional value superior to bovine milk and homologous to human milk, thus CM is considered an excellent alternative to human milk in cases where the acquisition of human milk is limited. Camel milk has a satisfactory balance of essential amino acids for human diets, contains a high percentage of easily hydrolysed β-ca seins, and lacks allergy-inducing β-lactoglobulin (El-Agamy, 2009; Hinz et al., 2012; Kappeler et al., 2003). Camel milk also contains high vitamin and mineral contents, and many protective proteins (e.g. im munoglobulins, lactoferrin, lysozyme, and lactoperoxidase) that have anti-cancer, anti-diabetic, and anti-bacterial properties (Barłowska et al., 2011; Konuspayeva et al., 2009; Zou et al., 2021a, 2021b).

Despite profound nutritional value of CM, its global supply and the food products produced from CM are very limited. The current uti lisation of CM is much below its potential. The production of CM products is highly challenging, but in the last decade many attempts have been made to optimise the processing conditions to produce high- quality CM products with a long shelf life, which is necessary to enable worldwide distribution of CM. Although many review papers on CM exist in the literature (e.g. Farah, 1993; G. Konuspayeva & Faye, 2021; G.

Konuspayeva, Faye, & Duteurtre, 2021; G. Konuspayeva, Faye, & Loi seau, 2009; G.S. Konuspayeva, 2020a,b; Kula & Tegegne, 2016; Shori,

2015; Yadav, Kumar, Priyadarshini, & Singh, 2015), most are dedicated to describing the composition and nutritional properties of CM, and general production of some kinds of CM products. There is still a lack of comprehensive review focusing on technical aspects of the production of all possibilities of CM products. Therefore, in this review, we focus on the description of the potential production of food products from CM, including pasteurised/sterilised milk, foaming agent, powder, ice cream, cheese, butter, and yoghurt. Along with an update of the current pro duction of CM products, we also point out challenges and limitations in

* Corresponding authors.

E-mail addresses: minh.ho@helsinki.fi (T.M. Ho), n.bansal@uq.edu.au (N. Bansal).

Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres https://doi.org/10.1016/j.foodres.2021.110870

Received 16 August 2021; Received in revised form 23 November 2021; Accepted 2 December 2021

Food Research International 153 (2022) 110870 2 the processing procedures, where applicable. However, understanding the difficulties in producing CM products requires knowledge regarding the properties of CM. Therefore, CM composition, its nutritional value, functionalities, and stability during heat treatment are also presented in this review.

2. Macro-nutrients and bioactive compounds in camel milk

Camel milk composition has been studied throughout the world, and a large number of available references show large variations. A meta- analysis of the literature data of CM composition was published in 2009 (Konuspayeva et al., 2009), and updated in 2020 (Konuspayeva 2020b).

The composition of dromedary CM from various geographical origins, taken from this meta-analysis, is summarised along with those of bovine and human milk in Table 1.

2.1. Proteins Caseins in CM account for 61.8–88.5% of the total protein (Ereifej et al., 2011). The components of camel caseins, including αS1-casein, αS2-casein, β-casein, and kappa-casein constitute 21, 10, 65, and 3.5% of the total caseins, respectively (Kappeler et al., 2003; Mati et al., 2017).

Similar to human milk, CM contains a high percentage of β-casein (65% of total caseins) (Kappeler et al., 2003). As β-casein is less resistant to peptide hydrolysis than αS-casein, its abundance in CM is considered to be one of the major reasons for easy digestibility of CM to human infants (El-Agamy et al., 2009). The amino acid composition of camel and bovine milk casein fractions is quite similar, except that camel caseins contain less cysteine and more proline (Kappeler, 1998).

Camel milk whey proteins mainly comprise α-lactalbumin, serum albumin, immunoglobulins, lactophorin (also called glycosylation- dependent cell adhesion molecule-1 or GlyCAM-1), and lactoferrin.

The concentrations of α-lactalbumin, serum albumin, and lactoferrin in

CM were determined to be 2.01, 0.40, and 1.74 mg/mL, respectively, by capillary electrophoresis (Omar et al., 2016). The high content of α-lactalbumin and lactoferrin, and the absence of β-lactoglobulin in CM are very similar to human milk (Hinz et al., 2012). As β-lactoglobulin is one of the major allergens in bovine milk, its absence in CM makes it a promising alternative protein source in infant formula. Studies show that CM can be considered as an alternative to human milk due to hy poallergenic properties of its proteins (El-Agamy, 2007).

A range of bioactive proteins with potential antimicrobial activity has been identified in CM, including lactoferrin, GlyCAM-1, immuno globulins, lactoperoxidase, peptidoglycan recognition protein (PGRP), lysozyme, and whey acidic protein (Mati et al., 2017). The physi ochemical properties and bioactivities of these proteins are summarised in Table 2. Mati et al. (2017) presented a comprehensive review on the potential biological activities of the CM proteins and their peptides released during fermentation/digestion.

2.2. Lipids Camel milk fat content was found to closely relate to the geographical origin according to the meta-analysis results of CM composition (Table 1). The fatty acid composition of CM was well described and compared with cow and human milk in a study reported by Dreiucker and Vetter (2011). Camel milk fat only contains small amounts of short-chain fatty acids (C4–C12) but a higher concentration of long-chain saturated fatty acids compared with bovine and human milk fats. The highest concentration of branched-chain fatty acids was observed in CM fat (3.03%), compared with 1.82 and 0.36% in bovine and human milk fats, respectively (Dreiucker & Vetter, 2011).

Regarding cis-monoenoic fatty acids, CM fat also contained a high concentration of palmitoleic acid, 16:1 cis-9 (10.1%) in addition to oleic acid, 18:1 cis-9 (17.2%) (Dreiucker & Vetter, 2011).

Camel milk fat showed melting point and solidification temperatures at 41.9 and 30.5 ◦C, respectively, while those of bovine milk fat were

32.6 and 22.8 ◦C, respectively. The increased melting point of CM fat may result from its high content of long-chain fatty acids, low content of short-chain fatty acids, and trans18:1 isomers (Abu-Lehia, 1989). The milk fat melting profile is dominated by the higher molecular weight triacylglycerols (TAGs, ≥C40). The low levels (<1%) of TAG C24–C40 and very high levels of TAG C48–C52 in CM fat were regarded as the main reasons for its relatively higher melting temperature compared with those observed for bovine, goat, sheep, horse, donkey, and water buffalo milk in the same study (Smiddy et al., 2012).

The average diameter of the milk fat globules follows an ascending order for camel (2.99 μm), goat (3.2 μm), sheep (3.78 μm), bovine (3.95 μm), and buffalo (8.7 μm) milk. Relatively smaller fat globules size (from

0.1 to 4.0 μm) comprise 80.6, 68.4, 55.3, 73.3, and 23%, of the total fat distribution in camel, bovine, sheep, goat, and buffalo milk, respectively (El-Zeini, 2006). As small fat globules are more vulnerable to lipolytic enzymes, camel and goat milk are believed to be more easily digested by humans (Tomotake et al., 2006).

2.3. Lactose The lactose content of dromedary CM is similar to that of bovine milk (Table 1). The CM lactose content was found to be low at birth of the calf (2.8%, w/v) and increased to 3.8% within first-day lactation. The average lactose content increased to 5% in camels with free access to drinking water, while it decreased to 2.9% in dehydrated camels.

Lactose concentration variation in CM has been considered one of the major reasons for the reported differences in its taste (occasionally sweet and occasionally bitter) (Yagil & Etzion, 1980). Interestingly, CM seems to be a safer and healthier option for patients suffering from lactose intolerance. One possible reason for the easy digestibility of CM is the lower concentration of casomorphin in CM that provokes reduced in testinal motility, thus exposing lactose more to lactase action over a longer period (Cardoso, et al., 2010). Another possible reason for low lactose intolerance of CM compared to bovine milk is due to the high content of L-lactate in raw CM which is 100 times more than that in bovine milk (Konuspayeva et al. 2019).

2.4. Minerals and vitamins The average ash content in dromedary CM is similar to that in bovine milk but much higher than that in human milk (Table 1). The mean values (mg/100 g) of major CM minerals are: calcium 111.4; magnesium

6.7; phosphorus 81.2; sodium 57.8; potassium 156.3, while the corre sponding concentrations in bovine milk are 119.9, 13.4, 95.0, 49.7, and

147.0, respectively. The respective concentrations of these minerals are much lower in human milk: 32.4, 3.4, 14.0, 16.0, and 51.8 mg/100 g, respectively (Soliman, 2005). The Ca:P ratios for camel, bovine, and human milk are 1.5, 1.29 and 2.1, respectively. As a high level of phosphate in infant formula may cause hyperphosphatemia and low serum calcium, a CM-based formula is considered to be better for feeding infants (Kappeler, 1998). In addition, the iron concentration in

CM is six times higher compared with bovine milk (Sawaya et al., 1984;

Table 1 Composition of camel, bovine and human milk.

Milk type Composition (%, w/v) Protein Fat Lactose

Ash Camel milk - East Africa 3.33 ± 0.52 4.14 ± 0.80

4.18 ± 0.72 0.76 ± 0.09 - North Africa 3.21 ± 0.60

3.50 ± 1.01 4.65 ± 0.67 0.84 ± 0.08 - Indian subcontinent

3.36 ± 0.64 3.49 ± 0.85 4.45 ± 0.74 0.77 ± 0.07 - Western Asia

3.10 ± 0.62 3.31 ± 1.03 4.45 ± 0.40 0.78 ± 0.05 - Undetermined

3.34 ± 0.53 3.62 ± 0.81 4.49 ± 0.77 0.72 ± 0.07 Bovine milk

3.20–3.80 3.70–4.40 4.80–4.90 0.70–0.80 Human milk

1.10–1.30 3.30–4.70 6.80–6.90 0.20–0.30 T.M. Ho et al.

Food Research International 153 (2022) 110870 3 Ziane et al., 2016).

Camel milk contains a wide range of vitamins, including vitamins A,

C, D, E, and the vitamin B group. Camel milk is known for its high vitamin C content, which is three to five times as high as that in bovine milk (Farah et al., 1992). The vitamin B3 concentration is also higher in

CM compared with bovine milk, whereas bovine milk contains more vitamins A and B2 (Farah et al., 1992; Haddadin et al., 2008; Sawaya et al., 1984; Stahl et al., 2006). Camel and bovine milk contain similar levels of vitamins B1 and B6 (Haddadin et al., 2008; Sawaya et al.,

1984). A comprehensive review about different types of vitamins in CM was recently published (Faye et al., 2019).

3. Biological functionalities of camel milk 3.1. Hypoglycaemic effect

The consumption of CM for treating diabetes has a long tradition in camel-rich regions (Mohamad et al., 2009). A significantly lower prev alence of diabetes was found in a CM-consuming community in Rajas than, India compared with another community where CM was not consumed (0 vs. 5.5%) (Agrawal et al., 2007). Dozens of clinical studies have confirmed the anti-diabetic effects of CM. According to Agrawal et al. (2003), type I diabetes patients required 30% less insulin after drinking CM for three months. Besides, the long-term efficacy and safety of CM as an adjuvant therapy for the treatment of type I diabetes were confirmed after 1- and 2-year trials (Agrawal et al., 2011; Agrawal et al.,

2007). Camel milk may also help control the insulin levels of patients with type II diabetes, as a significant increase in insulin levels was observed after two months of CM consumption (Ejtahed et al., 2015).

The hypoglycaemic effect of CM was also investigated in animal models.

The blood glucose levels in diabetic rabbits and dogs decreased by 78 and 47%, respectively, after receiving CM for four to five weeks (Sboui et al., 2010; Tantawy et al., 2010).

The anti-diabetic property of CM was previously considered to be mainly due to its high content of insulin and insulin-like proteins (Korish et al., 2015; Malik et al., 2012). However, in a recent study, Abou- Soliman et al. (2020) performed an in vitro digestion of CM and found no insulin activity after 30 min of gastric digestion. Insulin digestion was further confirmed by negative results in enzyme-linked immunosorbent assay (ELISA) in their study. More in vivo studies are needed to confirm the absorption of orally administered CM insulin and insulin-like pro teins. Other elements in CM may also potentially contribute to its anti- diabetic activity. For example, antioxidants in CM may also be capable of regulating hyperglycaemic states in humans (Limon et al., 2014).

3.2. Antimicrobial effect Camel milk showed antibacterial activity towards both Gram- positive and Gram-negative bacteria such as Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, Salmonella typhimurium, Klebsiella pneumonia, and Clostridium perfringens (Benkerroum et al., 2004; El

Agamy & Ruppanneb, 1992; Othman, 2016). The antibacterial activity of CM offers help for diseases that are caused by bacterial infections, such as tuberculosis (TB) and Crohn’s disease (Mal et al., 2000; Shabo et al., 2008). Besides eliminating pathogenic bacteria (Mycobacterium tuberculosis for TB and Mycobacterium avium - subspecies paratuberculosis for Crohn’s disease, respectively), bioactive proteins in CM, such as immunoglobulins, are believed to help boost immunity, which also benefits the healing process (Mal et al., 2006). Symptom alleviation is, therefore, usually regarded as the joint efforts of bactericidal and immunological effects of CM.

The antibacterial activity of CM is mainly due to its bioactive com pounds, especially lactoferrin, lysozyme, and immunoglobulins, which are most abundant in CM (Benkerroum et al., 2004; El Agamy & Rup panneb, 1992). Besides, the antimicrobial activity of camel whey pro teins was improved after enzymatic hydrolysis, suggesting that certain peptides with stronger antimicrobial activity may also be released after in vivo digestion (Salami et al., 2010). Lactoferrin in CM also exhibited antiviral activity towards hepatitis C virus genotype 4. Entry of the virus into the leucocytes was completely inhibited in the presence of camel lactoferrin (Redwan & Tabll, 2007). Antifungal and antiparasitic activ ities in CM have also been claimed (Maghraby et al., 2005).

3.3. Immunological effect Camels have a unique and powerful immune system. Camel anti bodies are reportedly much smaller in size compared with their coun terparts in humans. Additionally, IgG2 and IgG3 in CM are unique due to a natural absence of light chains (Riechmann & Muyldermans, 1999).

The small size of camel immunoglobulins (Igs) is believed to be

Table 2 Physico-chemical properties and bioactivities of bioactive proteins in camel milk.

Bioactive protein Accession No. or NCBI reference No.

Molecular mass (kDa) pI Amino acid residues Bioactivities

Lactoferrin Q9TUM0 75.3 8.63 689 Immunomodulation;

Antibacterial activity; Antiviral activity Immunoglobulins

Maternal immunity transfer; Toxin-neutralizing activity;

Enzyme antigen inhibitor IgAs_light and heavy chains n.d.*

22.5 and 55.5 n.d. n.d.

IgMs_light and heavy chains n.d.

27.0 and 80.0 n.d. n.d.

IgGs1_light and heavy chains n.d.

30.0 and 50.0 n.d. n.d.

Heavy-chain IgGs2 n.d.

46.0 n.d. n.d.

Heavy-chain IgGs3 n.d.

43.0 n.d. n.d.

GlyCAM-1 Antibacterial activity; Mastitis prevention

Variant A P15522 15.4 5.2 137 Variant B P15522 13.7

5.93 122 PGRP-1 Q9GK12 19.1 9.02 172 Antibacterial activity;

Microbiome modulator; Anti-inflammatory activity Lactoperoxidase

NP_001290481 69.7 8.87 613 Antibacterial activity Lysozyme

XP_010984684 14.9 6.33 130 Antibacterial activity WAP

P09837 12.6 4.86 117 Antibacterial activity; Anticancer activity;

Protease inhibitor Source: Elagamy et al. (1996); Hamers-Casterman et al. (1993); Mati et al. (2017).

* not determined.

T.M. Ho et al.

Food Research International 153 (2022) 110870 4 beneficial in targeting specific antigens. Camel IgG shows a complete neutralising activity against tetanus toxin and is recognized as a better inhibitor of enzyme antigens (Muyldermans et al., 2001; Riechmann &

Muyldermans, 1999).

Camel milk therapy showed a surprisingly positive effect on the behaviour of autistic children. Though the cause of autism remains unknown, studies propose it to be related to an increase in oxidative stress. After two weeks of CM consumption, glutathione, myeloperox idase, and superoxide dismutase concentrations were found to increase significantly in the plasma of autistic children, which benefits the con trol of oxidative stress (Shabo & Yagil, 2005). The immune system rehabilitative effect of Igs in CM is also regarded as a possible factor alleviating the potential dairy food allergy in autistic children (Al- Ayadhi et al., 2015).

3.4. Hypoallergenicity Bovine milk allergy is one of the main food allergies reported in children and adults. The clinical symptoms vary and can be quite severe.

Bovine milk contains over 20 proteins that can cause allergic reactions.

Casein fractions (particularly αS1-casein) and β-lactoglobulin are the two most powerful of these allergens (El-Agamy, 2007). A compositional analysis of human milk showed it to contain no β-lactoglobulin, and a low concentration of αS1-casein but a high concentration of β-casein (El- Agamy et al., 2009). The protein constituents in CM are similar to those in human milk, suggesting its high potential to serve as an alternative to bovine milk for children with allergies (El-Agamy, 2007). Encouraging results were also observed from clinical trials when CM was used to treat children with milk allergies (Shabo et al., 2005). Camel milk was even claimed to be a better choice for lactose-intolerant people, as they rapidly digested lactose in CM (Cardoso et al., 2010). Still, larger-scale trials are needed to make a stronger claim.

3.5. Angiotension I-converting enzyme (ACE) inhibitory activity

Angiotension I-converting enzyme (ACE) is a dipeptidyl carboxy peptidase that regulates blood pressure, and ACE inhibition results in a fall of blood pressure. Peptides that have ACE-inhibitory activity are found in various food proteins, including milk proteins (Minervini et al.,

2003). ACE-inhibitory peptides were also found in CM hydrolysates and fermented CM (Soleymanzadeh et al., 2019; Tagliazucchi et al., 2016).

In a study by Quan et al. (2008), an ACE-inhibitory peptide (AIPPKKNQD) was purified from fermented CM. This peptide main tained its ACE-inhibitory activity after either protease digestion or heat treatment, indicating its anti-hypertensive potential after in vivo digestion.

4. Effect of heat treatment on the nutritional value of camel milk

4.1. Heat stability of camel milk The heat stability of milk is an important parameter when consid ering its thermal processing. The heat coagulation time (HCT) of CM at

100, 120, and 130 ◦C was investigated at pH 6.3–7.1 (Farah & Atkins,

1992). At 120 and 130 ◦C, the milk was very unstable at all pH values, with HCT below 2–3 min. At 100 ◦C, HCT initially increased to 12 min, then remained constant between pH 6.4 and 6.7, and increased pro gressively with increasing pH, reaching approximately 33 min at pH 7.1.

Camel milk seemed to be much less heat stable compared with bovine milk (Farah, 1993). In another study, the HCTs for bovine, buffalo, and

CM were determined to be 1807.4, 1574.6, and 133.6 s, respectively, at

140 ◦C (Shyam et al., 2016).

The presence of kappa-casein and β-lactoglobulin and their interac tion during heating is believed to be critical in maintaining milk stability (Farah & Atkins, 1992). Therefore, the reduced level of kappa-casein (5% of total casein in CM compared with 13.6% in bovine milk) and the absence of β-lactoglobulin may be responsible for the poor stability of CM at high temperatures.

4.2. Heat stability of camel milk proteins To develop a suitable heat processing technique for CM, it is neces sary to study the heat stability of CM proteins to see whether their functionality can be maintained during heat treatment. Different heat ing conditions have been applied to CM proteins in different studies.

Camel milk whey proteins were more heat resistant than bovine and buffalo milk proteins when the milk was heated to 63, 80, and 90 ◦C for

30 min (Farah, 1986) or to 65, 75, 85, and 100 ◦C for 10, 20, and 30 min (Elagamy, 2000). The heat stability of camel and bovine whey proteins was also measured indirectly by assessing the solubility change after the separated whey fractions at pH 4.0, 4.5, 5.0, and 7.0 were heated at

60–100 ◦C for 1 h, given that the denatured proteins would precipitate after heating and cause a drop in whey protein solubility (Laleye et al.,

2008). The effect of temperature on solubility depended on pH, and a major change in solubility occurred at pH 4.5, which is the isoelectric point of many whey proteins. Both bovine and camel whey proteins were most stable at pH 7, a level at which the aggregation process is inhibited by electrostatic repulsion between the unfolding globules. At pH 4.5 and 100 ◦C, a decrease in solubility by 55 and 52% was observed for camel and bovine whey proteins, respectively. Camel whey proteins were found to be more susceptible to acid denaturation, as solubility decreased by approximately 16% in camel and 9% in bovine whey as pH was dropped from 7 to 4. According to Felfoul et al. (2015), the bands of camel serum albumin, α-lactalbumin, and kappa-casein decreased after heating at 90 ◦C. Bovine serum albumin was not seen in the electro phoresis patterns after heating bovine milk at 70 ◦C, while β-lacto globulin and α-lactalbumin bands were removed only at 90 ◦C. In addition, the free thiol group concentration analysis results indicated that no significant camel protein denaturation happened at 70 ◦C, while the complete denaturation of bovine milk occurred after heat treatment at 70 ◦C for 30 min. Recently, Genene et al. (2019) also observed, through whey protein nitrogen analysis after heat treatment of the milk samples, that CM whey proteins were less heat-denatured compared with bovine milk whey proteins. SDS-PAGE results in the same study showed that 33% of α-lactalbumin was denatured in CM after heating at

90 ◦C for 5 min, while the percentage was 95% in bovine milk.

Differential scanning calorimetry (DSC) has occasionally been used to measure the denaturation temperature of CM proteins. Concentrated

CM and bovine milk showed denaturation peaks at 77.8 and 81.7 ◦C, respectively (Felfoul et al., 2015). When liquid and dry, camel and bovine whey samples were analysed using DSC, dry camel whey showed three marginal thermal transitions at 139, 180, and 207 ◦C, while the three peaks appeared at 81, 146, and 198 ◦C for dry bovine whey.

However, no significant differences were observed in the heat dena turation curves of camel and bovine whey proteins in liquid form (Laleye et al., 2008). As protein mixtures exist in these peaks, the numbers may not be reliable enough to draw conclusions on whey protein stability.

Overall, CM whey proteins seem to be more heat stable than bovine milk whey proteins, although differences in milk origin, test conditions, and assay methods may result in inconsistencies in the above results.

These studies generally analyse whey proteins as a whole, and protein gels are sometimes used to follow changes in major whey proteins. More detailed studies on how whey proteins, especially ones with antimi crobial activity (some are relatively minor in milk), behave during heat treatment will be helpful for providing comprehensive information for

CM heating processing.

The thermostability of certain individual bioactive proteins in CM has also been investigated. Usually protein purification has to be per formed prior to stability analysis. The heat resistance among these camel whey proteins was ranked as lysozyme > lactoferrin > IgG (Elagamy,

2000). The secondary structure of camel α-lactalbumin was better pre served than that of bovine α-lactalbumin during heat denaturation (Atri

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Food Research International 153 (2022) 110870 5 et al., 2010). Lactoperoxidase in CM exhibited lower heat stability compared with that in bovine milk when heated to 67–73 ◦C (Tayefi- Nasrabadi et al., 2011).

Proteomic methods have also been applied in studies investigating the effect of heat treatment on CM proteins. Compared with traditional methods, they are able to efficiently quantify a large set of proteins simultaneously and provide a much more sensitive and accurate alter native for analysing the heat denaturation of individual CM proteins.

The changes in CM proteins after freezing, pasteurisation and spray drying were investigated and compared with bovine and caprine milk (Zhang et al., 2016). A total of 129, 125, and 74 proteins were quantified in bovine, camel, and caprine milk sera, respectively. Protein concen trations changed at different rates with varied processing steps and among different species. Some immune-related proteins were heat sen sitive, such as lactoferrin, GlyCAM 1, and lactapherin, with a loss of approximately 25 to 85% after pasteurisation and 85 to 95% after spray drying. Meanwhile, α-lactalbumin, osteopontin, and whey acidic protein were relatively heat stable, showing a loss of 10 to 50% after pasteur isation and 25 to 85% after spray drying. On the other hand, the con centrations of certain proteins originating from damaged milk fat globules and somatic cells increased after freezing.

Bovine and CM proteins before and after heat treatment at 80 ◦C for

60 min were identified using liquid chromatography coupled with tan dem mass spectrometry, LC-MS/MS (Felfoul et al., 2017). α-lactalbumin,

PGRP, and serum albumin were identified as the major whey proteins in

CM, in the following heat sensitivity order: α-lactalbumin < PGRP < serum albumin (100, 68, and 42% decrease observed after heating for α-lactalbumin, PGRP, and serum albumin, respectively). For the two major whey proteins, i.e. α-lactalbumin and β-lactoglobulin in bovine milk, 0 and 26% remained, respectively, after heat treatment. Moreover, a total of 19 protein bands were separated using SDS-PAGE and iden tified using LC-MS/MS. The results confirmed the vulnerability to heat treatment at 80 ◦C of camel α-lactalbumin and PGRP, along with bovine α-lactalbumin and β-lactoglobulin. Meanwhile, casein fractions in both camel and bovine milk remained intact after being heated at 80 ◦C for

60 min.

The denaturation of whey proteins in CM after heating at 63 ◦C and

98 ◦C for 1 h was investigated comprehensively by Quantitative 2D-dif ference in gel electrophoresis - mass spectrometry (Benabdelkamel et al.,

2017). Compared with proteins in the non-heated milk samples, a total of 80 proteins significantly decreased in the milk samples heated at

63 ◦C, while 25 proteins which remained stable in the 63 ◦C-heated milk significantly decreased in the 98 ◦C-heated milk samples. Enzymes were most severely damaged by heating, followed by binding proteins and cell adhesion proteins. Immune-related proteins comprised 5% of all the proteins affected by heat treatment.

Recently, two new studies were published investigating protein profile changes in spray-dried CM powder. Zouari et al. (2020) spray dried skim CM and bovine milk and used HPLC-MS for protein identi fication and quantification before and after drying. Proteins were less denatured in CM powder compared with bovine milk powder. After spray drying, concentrations of camel serum albumin and α-lactalbumin decreased by 14.1 and 3.3%, respectively, while concentrations of camel

PGRP and caseins remained constant or increased. The protein profiles of unprocessed CM, heated liquid CM (115 ◦C, 15 min), and CM powder were compared by Li et al. (2020). Proteins were labeled with tandem mass tag and subjected to LC-MS/MS analysis. Among the 807 proteins identified, 246 and 170 proteins changed significantly in heated liquid milk and milk powder, respectively, compared with unprocessed milk.

After processing, the most significantly decreased proteins included ARF

GTPase-activating protein GIT1, elongation factor 1-α 1, Acyl-CoA desaturase, heat shock protein 90, and aldehyde oxidase 3-like pro tein. As bactrian CM was used in the study, the protein composition may be somewhat different from that of dromedary CM, which was used in other studies mentioned above.

Different processing conditions, along with analytical methods, may result in some of the inconsistent results described above. For example, α-lactalbumin was less heat stable than serum albumin in CM in Felfoul et al.’s study (2017) but more heat stable in Zouari et al.’s study (2020).

Research concerning the influence of heat on CM proteome is still at an early stage. More studies are still required to show how various pro cesses affect camel milk proteome, especially the bioactive proteins.

5. Possible food products produced from camel milk

5.1. Pasteurised and sterilised camel milk Physically, CM is analogous to cow milk with its white colour, and slightly salty with a sweet aftertaste. Compared with cow milk, CM contains higher levels of minerals (e.g. iron), vitamin C, antibacterial and probiotic compounds, a higher ratio of whey proteins to caseins, and lacks allergy-inducing proteins (β-lactoglobulin). These factors make CM more readily digestible than cow milk, and closest to human milk in terms of nutritional values (El-Agamy, 2006). Due to higher concen tration of antimicrobial components, raw (fresh) CM has a longer shelf life than cow milk (Faraz et al., 2013). Activating the natural antimi crobial system (e.g. the lactoperoxidase system) in CM with hydrogen peroxide-producing lactic acid bacteria, such as W. confusa 22282, was reported as an alternative approach to maintaining the storage stability of raw CM (Dashe et al., 2020). From the nutritional aspect, it is feasible to process CM for human consumption similarly to cow milk. However, use of CM for daily human consumption is still limited although CM is available on the market in many countries. A list of suppliers for CM, which is obtained from the Alibaba sales platform, was described in study by Konuspayeva et al. (2021). Most CM products are pasteurised milks that are heated at approximately 72 ◦C for 15 s to kill harmful pathogens, allowing the product to be kept for two weeks at refrigera tion temperature (Ipsen, 2017). Studies show that pasteurising CM is possible under the same regimes used for cow milk without causing any significant alteration in its functionality. At temperatures less than

100 ◦C, whey proteins and antimicrobial factors in CM were significantly more stable than those in cow milk (Elagamy, 2000; Farah, 1986), and the thermal inactivation of pathogenic bacteria (e.g. Escherichia coli) in

CM and cow milk was similar (Sela et al., 2003).

Commercially pasteurised CM is unhomogenised. During its storage, a thin layer of white cream forms on top as a result of creaming. The creaming rate of CM is much slower than that of cow milk under the same conditions. At 4 ◦C, creaming of CM after 24 h was twelve times less than that of cow milk (Farah & Rüegg, 1991). Homogenisation may therefore not be necessary for pasteurised CM, as its shelf life is quite short. The slow creaming of CM is attributed to its small fat globule size.

As shown in Fig. 1 (unpublished data), which exhibits the particle size distributions of raw cow milk and CM, the average particle size of CM derived from particle volume (D[4,3]) was 2.56 µm, while the average

Fig. 1. Particle size distribution of raw camel and cow milk (Ho et al., 2021).

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Food Research International 153 (2022) 110870 6 particle size of cow milk was almost double (4.16 µm). Moreover, a deficiency in agglutinin (a protein promoting the clustering of fat globules) in CM contributes to its low creaming ability (Farah & Rüegg,

1991). Although there are many health benefits of drinking CM, extremely high retail price (e.g. USA: ~38 USD/L, Singapore: ~19 USD/

L, Australia: ~15 USD/L, India: ~7 USD/L), due to low yield and high production costs, may be the main reason for its limited use for human consumption.

Camel milk has very poor heat stability at high temperatures and cannot be sterilised at natural pH due to denaturation and protein sedimentation. Producing sterilised CM is therefore very difficult. It was described in section 4.1 that the coagulation time of CM was reduced from 12 min to <1 min with increasing heating temperature from 100 ◦C to 140 ◦C (Farah & Atkins, 1992). The low stability of CM at high temperatures is associated with a deficiency of kappa-casein and an absence of β-lactoglobulin. However, heat stability of CM at high tem peratures increases with increasing pH and the presence of phosphate.

Increasing to a pH of 6.9–7.2 or adding sodium phosphate (1 mmol/L) to

CM did not cause any sedimentation of proteins or very little reversible sedimentation as it was heated at 121 ◦C for 15 min (Alhaj et al., 2011).

Compared to pasteurisation (72.5 ◦C/15 s) and high-pressure treatment (200–800 MPa), UHT (144 ◦C/5s) led to the greatest colour change and highest whey protein denaturation in CM (Omar et al., 2018). The denaturation level of α-lactalbumin in UHT CM was approximately 66%, which is nearly double to that measured in high-pressure-treated CM (~33%) and pasteurised CM (~27%). Regarding colour, the total colour difference (ΔE) value (indicating colour differences between untreated and treated milk samples) of UHT milk was 6.5, while pasteurised and high-pressure-treated milk had ΔE’s of 1.5 and 2.26, respectively. Also, treatment with pressures higher than 400 MPa and UHT inhibited rennet coagulation in CM. This study reinforces the challenges faced in the sterilisation of CM and indicates high-pressure treatment (<400 MPa) as a possible alternative for CM preservation because it has less negative effect on CM properties than UHT.

Future research directions for UHT of CM include studying the pos sibilities of various additives, such as disodium phosphate, kappa-casein from cow milk and calcium-chelating agents (e.g. ethyl enediaminetetraacetic acid disodium salts) to stabilise CM proteins, and hydrocolloids to increase the viscosity and reduce the sedimentation of

UHT CM (Alhaj et al., 2011). Small changes in pH seem to result in large effects on CM heat stability as kappa-casein and calcium content are the main factors affecting the heat stability of CM (Alhaj et al., 2011).

Currently, Camelicious (Emirates Industry for Camel Milk & Products) is globally marketing a UHT CM product with a shelf life of 12 months when stored in a cool and dry place (Yirda et al., 2020). However, it is produced from reconstituted whole CM powder.

5.2. Foam agents The top foam layer of many dairy products, such as cappuccino-style beverages, determines overall product quality and consumer accep tance. In most coffee shops, foam is prepared from cow milk, which may not be suitable for people with dairy allergies due to the allergy-inducing proteins in cow milk. Camel milk becomes a potential alternative for preparing foam because it lacks the allergen β-lactoglobulin. The foaming properties of CM and its proteins are comparable to those of cow milk under various temperature and pH conditions (Laleye et al.,

2008).

The foamability and foam stability of camel sweet whey proteins (separated from rennet gels by centrifugation) at pH 7.0 were only slightly inferior to those of bovine sweet whey proteins (Laleye et al.,

2008). However, after heat treatments were applied at 70 ◦C and 90 ◦C, camel acid whey proteins (obtained after acidification of fresh CM until pH 4.3, followed by centrifugation) exhibited much higher foamability and foam stability than their bovine counterparts (Lajnaf et al., 2018).

At pH < 5.0, camel α-lactalbumins lose their bound Ca2+ and exist in a molten globular state with high surface activity providing better adsorption at the interface and higher intermolecular interactions to form a viscoelastic film (Lam & Nickerson, 2015). Camel α-lactalbumin accounts for a high proportion (>70%) in acid whey proteins, thus acid whey proteins exhibited good foaming behaviour. In pure form, β-casein exhibited the higher foaming properties compared to α-lactalbumin (Lajnaf et al., 2017). Heat treatment of CM (70–100 ◦C/30 min) also improved the foaming properties due to heat denaturation and aggre gation of CM proteins, which led to an increase in surface hydropho bicity and a decrease in electronegative charge and interfacial tension.

Also, changes in secondary structure and its high hydrophobicity induced by heating are other reasons for the improved foaming prop erties of CM proteins (Lajnaf et al., 2020). These findings will be bene ficial to dairy processors, as they are helpful for evaluating the potential for commercial use of CM foam in cappuccino-style beverages.

5.3. Powder The production of dried CM powder without impairing its bioactive components has emerged as an important approach to making CM available worldwide and extending its shelf life, reducing the trans portation costs and expanding the applications of CM. Many CM powder products, some of which are non-branded, are available on the market.

Most are produced using a freeze drying technique because the low drying temperature in freeze drying helps to protect the bioactive compounds in CM, especially the functional properties of its proteins.

Freeze drying CM reportedly does not induce any significant alterations to nutritional properties (e.g. minerals, vitamins, amino acid composi tion, biological value, protein efficiency ratio, net protein utilization, and fatty acid profile) compared with those of fresh CM (Ibrahim &

Khalifa, 2015). Other physicochemical properties, such as the colour, flowability, density, and composition of CM and cow milk powders did not differ when produced under similar freeze drying conditions and were similar to those of commercial cow milk powders, except for CM powder insolubility, which was twice as high as cow milk powder (Sulieman et al., 2018). However, freeze drying is well known as a time consuming and expensive dehydration technique, and is not suitable for large-scale production of dried milk powders (Ortega-Rivas et al., 2005).

Moreover, after freeze drying, CM powder must be ground and sieved to obtain desirable homogeneity in powder particle size. The high price of

CM together with the high cost of freeze drying operations leads to the extremely high cost of CM powder.

Spray drying has been considered the most suitable unit operation for producing dairy powders. However, compared with bovine milk powders, the production of CM powders using spray drying is still at an early stage of research and development. Spray drying at a low tem perature (<60 ◦C) may be applicable for CM powder production, and there are a few spray-dried CM powder products available on the mar ket. Due to a lack of information concerning nutritional facts and dif ferences in the chemical composition of CM from various sources, performing a comparison of the nutritional values of CM powder pro duced by spray drying and freeze drying is impossible. Several reports exist regarding the spray drying of CM (Habtegebriel et al., 2018a,

2018b; Ho et al., 2019; Ho et al., 2021; Ogolla et al., 2019; Sulieman et al., 2014; Zouari et al., 2018; Ho et al., 2020). These studies are dedicated to observing the influences of spray drying operating condi tions (inlet air temperature, outlet air temperature, drying air flow rate, feed flow rate, feed direction, and atomisation pressure) and feed ma terial properties (solid concentration and fat content) on the physical, optical, and thermal properties of produced CM powders (yield, bulk density, colour, solubility, particle morphology, glass transition tem perature, water activity, vitamin C recovery, fatty acid profile). Gener ally, spray drying CM with the concurrent flow direction yielded better results on CM powder quality in terms of water activity, degree of lightness, solubility, fluidity, and powder yield (Sulieman et al., 2014).

Moreover, the yield of spray-dried CM powder was also determined by

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Food Research International 153 (2022) 110870 7 inlet air-drying temperature, feed flow rate, and solid feed content. The yield increased with increasing inlet air-drying temperature and feed flow rate but declined with increasing solid content in the feed (Hab tegebriel et al., 2018a, 2018b).

Spray drying CM at a higher temperature, higher feed flow rate, and with a high fat content declined the reconstitution properties of the powder (wettability, dispersibility, and solubility) (Habtegebriel et al.,

2018a; Ogolla et al., 2019). Fresh CM powder produced by spray drying at 160 and 70 ◦C of inlet and outlet air-drying temperature, respectively, had a very high solubility (98.62 ± 1.47%), and this solubility just slightly reduced during accelerated storage at 37 ◦C and low relative humidity levels (<33%) over 18 weeks (Ho et al., 2019). During storage, increasing surface lipid content leading to the increase in surface hy drophobicity and slight agglomeration of the powder particles is the main cause for the decline of the CM powder solubility with increasing storage time and increasing RH (Ho et al., 2021). High solubility of spray-dried CM powder allows many applications in food processing, as rehydration is a prerequisite for the incorporation of milk powder in food products. Spray-dried CM powder has been investigated as a new functional source for replacing the cheese base in the manufacture of processed cheese sauces. An addition of 10% spray-dried CM powder significantly improved the quality attributes, especially the sensory properties of cheese sauces (Desouky et al., 2019).

In terms of particle morphology, spray-dried CM powders had a smooth surface covered with fat layers and no crystalline structure (Habtegebriel et al., 2018a; Ho et al., 2019; Ogolla et al., 2019). Zouari et al. (2020a) found that the surface roughness of spray-dried CM was much lower than that of its bovine milk counterparts, and most of the

CM fat globules were encapsulated by the proteins near the powder surface during droplet formation. However, in a study by Ho et al. (2021), results of X-ray photoelectron spectroscopic analysis indicated that the surface of the fresh spray-dried camel milk powders was dominated by lipids (~78%), followed by proteins (~16%) and lactose (~6%). Increasing the surface lipid content during storage (e.g. 33% RH for 18 weeks) caused the agglomeration of powder particles which had wrinkled and folded surface with some dents and large vacuoles con taining small, dried milk particles (Fig. 2a and 2b). In addition, X-ray diffraction analysis of fresh spray-dried CM powders revealed some degree of crystallinity in the powders as some small sharp peaks were observed in their X-ray diffractogram (Fig. 2c) (Ho et al., 2019). Ana lyses of the biochemical properties of spray-dried CM revealed that the α- and β-caseins were very stable during spray drying, while about 14% of serum albumin was denatured (Zouari et al., 2020b). Also, the whey protein nitrogen index of spray-dried CM (~11.5%) was similar to that of its bovine milk powder counterpart (~9.0%). These studies strengthen the possibility of producing CM powder via spray drying.

However, further studies are required, particularly those examining the retention of bio-functionality in CM after spray drying.

There are many possible limitations for both laboratory- and factory- scale application of spray drying in CM powder production. Firstly, production of CM is limited to certain geographical locations, such as several Asian and Africa countries and Australia. Importantly, high temperature operation in the preconcentration (to increase the solid concentration of CM) and spray drying stages possibly will denature the nutritional and functional proteins in CM (Lajnaf et al., 2018). Due to the low solid concentration (~10%, w/w), it is not economical to perform spray drying of CM “as such”. In the production of milk powder, a preconcentration of milk to increase its solid concentration up to

40–50% (w/w) is an integral stage not only to reduce the energy con sumption of the drying process, but also to help impart desirable char acteristics to the dried powders (Roy et al., 2017). Recent advancements in the concentration and spray drying techniques possibly allow the preconcentration and spray drying of CM powder at low temperatures.

5.4. Ice cream Ice cream is a sweetened frozen product that is globally one of the most popular dairy desserts. It is typically produced from cow milk fortified with various ingredients. Due to the superior properties of CM to cow milk, the consumption of ice cream made from CM may be

Fig. 2. SEM of fresh spray-dried camel milk powder (a) and the powder kept at 33% RH for 18 weeks (b); and XRD of fresh spray-dried camel milk powder (c).

Adapted with permission from Ho et al. (2019).

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Food Research International 153 (2022) 110870 8 preferable to the cow milk product. Camel milk ice cream combines the benefits of both ice cream and CM to fulfil the requirements of the functional food (e.g. low-fat ice cream). Varieties of such products are currently available in the market. Basically, the production of CM ice cream is similar to that of cow milk counterpart, including the blending of ingredients, pasteurisation, homogenisation, cooling, aging (~4◦C), freezing via a scraped surface freezer (-5◦C) (or similar) under shear to incorporate air to form a foamed structure, adding flavouring in gredients (if applicable), packing, and blast freezing to temperatures of

−25 to −30 ◦C (Goff & Hartel, 2013). Camel milk ice cream has a lower melting point, lower dry matter content, and lower viscosity than cow milk ice cream when made with the same formulation. This is due to differences in the dry matter in CM and cow milk (10.02 and 12.30%, respectively). However, they are similar in fat and protein content, acidity, and sensory properties in terms of colour, flavour, texture, and mouthfeel (Jafarpour, 2017). Insignificant differences in consumer acceptance (texture, taste, flavour, and colour) were also reported for camel and cow ice cream (Hassan, 2009). Recent studies indicated that ice cream can be successfully processed from CM using various additives and flavourings to enrich the nutritional and health benefits, and to provide pleasant flavours to consumers (Ahmed & El Zubeir, 2015;

Salem et al., 2017). Fortifying CM ice cream with 2% CM casein and its hydrolysates increased its viscosity, consistency, and melting resistance, decreased its hardness and overrun, and enhanced its sensory properties (Hajian et al., 2020). The excellent surface-active properties of camel caseins in the formulations of low-fat creams and emulsions were also reported (Ziaeifar et al., 2018).

5.5. Butter Although CM fat content is quite similar to that of bovine milk (~2.30–3.95%), butter production from CM is very difficult, and the butter-making process from cow milk cannot be applied to CM due to differences in the physical and chemical nature of their fats and proteins.

Certain authors, therefore, claimed that butter cannot be made from CM (Yagil et al., 1994). Camel milk shows little tendency to creaming because of its lack of agglutinin (a protein promoting the clustering of fat globules) together with a small fat globule size and strong bonding of fat and proteins. In addition, the high melting temperature of CM fat, which is caused by the high proportion of long-chain fatty acids in the fatty acid profile and thicker fat globular membrane, makes the churning process of CM cream only accomplishable at higher temperatures than those commonly used for bovine milk (10–14 ◦C) (Asresie et al., 2013; Berhe et al., 2017; Farah & Fischer, 2004; Fuquay et al., 2011).

In fact, nomads in Sudan, Kenya, Egypt, Algeria, and Pakistan manually produced CM butter approximately 2 or 3 decades ago using fresh, soured or fermented CM, and CM cream. However, these manual processes were unable to obtain high yields of butter (El-Agamy, 2006).

Actually, controlled processes of CM butter making with improved butter yields were developed within the last two decades (Farah et al.,

1989), as shown in Fig. 3. In this process, CM was initially heated to

65 ◦C and centrifuged to separate the cream. After standardisation to

20–30% fat content, the cream was optionally inoculated with a 2% starter, to produce either a sour or sweet cream. Both sour and sweet creams were churned at 15–36 ◦C and the butter grains were washed in water at 27 ◦C. Results indicated that at the same fat content and churning temperature, the butter yield obtained from sour cream was markedly lower than that achieved from sweet cream. For sweet cream, highest butter yields (80–85.3%) are obtainable with cream at 20–25% fat content and churning temperatures of 15–20 ◦C, corresponding to a churning time of 10–18 min. In addition, no butter grains were obtained at a low churning temperature (<12 ◦C), while the butter yield signifi cantly declined as cream was churned at a temperature higher than

36 ◦C. Berhe et al. (2013) reported on another procedure to increase the butter yield from fermented CM (Fig. 3). Camel milk fermented at room temperature until pH 4.10 was subjected to vigorous churning in a vertical direction at 22–23 ◦C, rather than the back-and-for movement used in the traditional method. This method resulted in a high butter yield (~80%) due to the high churning force but very long churning time (~120 min). Although producing butter from CM is possible from a scientific viewpoint, competing with cow milk butter requires extensive further studies to address the limitations in the churning process and

Fig. 3. Process for making butter from camel milk.

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Food Research International 153 (2022) 110870 9 butter yield.

In terms of butter quality, CM butter is characterised with a white colour, stickiness, greasiness, high melting point, low content of short- chain fatty acids, and less flavour intensity. Camel milk butter is not only used as food for eating, as oil for food preparation and cooking, but also for medicinal purposes due to the probiotic characteristics of microflora used in traditional CM butter making (Ipsen, 2017; Maurad &

Meriem, 2008; Mourad & Nour-Eddine, 2006).

5.6. Cheese Producing cheese from CM is more difficult and complicated than from other mammalian milks (cow, buffalo, sheep, and goat) because of the long coagulation time, low yield, and weak coagulum (Ramet,

2001). Cheese firmness is determined by the ratio of kappa-casein to total caseins. The higher this ratio results in the firmer the cheese.

However, this ratio is about 3.5% in CM, which is much lower than in bovine milk (~13%) and buffalo milk (13–20%). In addition, camel kappa-casein has completely different cleavage sites for hydrolysis compared with its bovine counterpart. Chymosin cleavage sites of camel kappa-casein are at the Phe97-Ile98 amino acid sequence sites, while those of bovine milk are at Phe105-Met106. All these characteristics, together with high resistance of CM to bacterial growth due to its high content of antibacterial compounds, result in delaying the coagulation of

CM and the production of soft coagulum. The large size of casein mi celles is another feature of CM associated with its poor rennetability.

Camel casein micelles are approximately 380 nm in size, nearly double to that of bovine milk casein micelles (150 nm) (Berhe et al., 2017; El- Agamy, 2006). Despite these limitations of CM, numerous efforts have been made to produce various types of CM cheeses, and they are sum marised in Table 3. Details about production of CM cheeses at household scale by nomads are reviewed by El-Agamy (2006). Recently, Konus payeva (2020a) well described challenges in the production of CM cheeses regarding technological development, cultural satisfaction, and commercialisation.

A simple approach to producing CM cheese is to use a mixture of CM and other non-bovine milks, such as buffalo milk, to increase casein content. Soft unripened buffalo milk cheese had a higher yield (12.22% for buffalo milk vs. 5.49–7.68% for CM) and was superior in sensory and physical properties than its CM counterpart under the same processing conditions (Inayat et al., 2007). Therefore, mixing 30% (w/w) buffalo milk with CM improved the rennetability and firmness of curds, increased the yield, decreased weight loss during pickling, and enhanced the microbiological quality and sensory properties of the resultant cheese (Shahein et al., 2014). For similar reasons, mixing sheep milk with CM for the production of soft cheese has also been reported (Saadi et al., 2019).

Soft cheese is the most popular CM cheese. Several procedures are used to produce CM soft cheese using various coagulation agents.

Mohamed et al. (2013) found that fresh soft cheese with acceptable sensory properties could be simply prepared from CM via coagulation by direct acidification (60% acid acetic, pH 4.3). However, in a recent study by Mbye et al. (2020), the use of acetic acid (30% acid per liter of milk) as a coagulant in the production of soft unripened camel cheeses was reported to cause a pungent odor and sour taste of the product. In addition, Mehaia (1993) claimed that making CM cheese without using starter cultures was not encouraged, as this resulted in high moisture and pH, low yield, and poor sensory properties of the cheese. Ahmed and

Kanwal (2004) also stated that using starter cultures (S. cremoris and

S. lactis, isolated from CM) provided higher-quality CM soft cheese. Abu- Tarboush (1996) recommended using mixed cultures (S. thermophilus and L. delbrueckii ssp. bulgaricus) to archive desirable properties when producing CM cheese and yoghurt. These studies indicate the impor tance of starter cultures in CM cheese making. Different starter cultures were found to have various effects on the physicochemical and texture properties, and on consumer’s preferences of the product. Non-aromatic

Table 3 A summary of the research studies regarding camel milk cheese, with emphasis on cheese types and processing conditions.

Type of cheese Processing conditions References Fresh soft cheese

• Heating at 63 ◦C, 30 min • Acidification with 60% acid acetic, pH

= 4.3 • CaCl2, 3–4% Mohamed et al. (2013) Soft unripened cheese

• Heating at 65 ◦C, 30 min • CaCl2, 0.15% • Yogurt starter culture, S. thermophilus,

3% • Ginger crude extract Hailu et al. (2014) • Heating at 65 ◦C, 30 min

• CaCl2, 3.0% • Chymosin (1000 IMCU/ML milk), or citric or acetic acid (30% acid/L milk)

• Thermophilic yoghurt starter culture (Streptococcus thermophilus and

Lactobacillus delbrueckii subsp. bulgaricus), 3% (w/v)

Mbye et al., (2020) Fresh soft white cheese • Milk fat, 0–3%

• Salt, 0–3% • CaCl2, 0.03% (w/v) • Yogurt B-6 starter (S. thermophilus and

L. delbrueckii subsp. bulgaricus), 1.0% (w/w) • Lactic fermentation starter (L. lactis ssp. cremoris, L. lactis ssp. lactis, and L. lactis ssp. diacetylactis), 1.0% (w/w)

• Rennet, 0.004% (w/w) Mehaia (1993) Fresh cheese • Camel milk isolated LAB (S. cremoris and

S. lactis in a ratio of 95:5): 5.0% (w/v) • Rennet, 0.03% (w/v)

Ahmed and Kanwal (2004) • CaCl2, 0.03% • Camifloc**

El Zubeir and Jabreel (2008) Soft cheese • CaCl2 0.02% (w/v)

• Yogurt starter cultures (S. thermophilus and L. delbrueckii subsp. bulgaricus),

3.0% (w/v) • Chymosin Chy-MaxTM, 0.15–15% (v/v) Benkerroum et al. (2011)

• CaCl2, 0.1 mL/kg or Ca phosphate, 1 g/ kg • Rennet Chy-Max M, 50 µL/L

Konuspayeva et al. (2014) • CaCl2, 0.02–0.08% • Pasteurisation conditions, 60–75 ◦C/30 min

• pH 5.5–6.5 Qadeer et al. (2015) Fresh soft white cheese

• Camel milk retentate • CaCl2 0.02% (w/w) • Salt, 1.05% (w/w)

• Yoghurt starter cultures (B-6), 0.5% (w/ w) • Rennet**

Mehaia (2006) • CaCl2 0.05% (w/v) • 10% citric acid solution, pH = 5.5 or starter culture, 5%

• Rennet, 0.15 mL/L Khan et al. (2004) Soft white cheese

• CaCl2, 0.02 g/L • Starter culture (STI-12, RST-743, R-707,

XPL-2, CHN-22), 50U/500 mL • Camel chymosin, 85 IMCU/L*

Bekele et al. (2019) Dry-salted soft cheese • Starter (S. thermophilus, CHOOZIT star24TM), 3.0%

• Chymosin Chy-Max M1000, 50 µL/L • Salting in NaCl, 3% (w/w)

Konuspayeva et al. (2017) Brine-salted soft cheese

• Starter (S. thermophilus, CHOOZIT star24TM), 3.0%

• Chymosin Chy-Max M1000, 50 µL/L • Salting in saturated NaCl

Soft brined cheese • CaCl2 0.02% (w/v) • Starter culture (Str. thermophilus STI-12),

75 U/1000 L • Camel chymosin Chy-MaxTM, 55–85 IMCU/L*

• Curd brine NaCl, 2 and 5% (w/w) Hailu et al. (2018)

* IMCU: International milk clotting units; T.M. Ho et al.

Food Research International 153 (2022) 110870 10 cultures, such as STI-12, RST-743, and R-707, result in better curd firmness, cheese yield, cheese compositional quality, and texture, while aromatic cultures, such as XPL-2 and CHN-22, impart higher consumer preference for taste and aroma (Bekele et al., 2019).

The quality of CM soft cheese is dependent on many factors, ranging from processing conditions to the types of coagulants used. Studies concerning CM cheese making have, therefore, focused on optimising these factors. By varying heat treatments, pH, CaCl2 content, and buffalo milk ratios, Qadeer et al. (2015) reported that optimal processing con ditions for producing soft CM cheese at high yields (~22%), with short coagulation times (~30 min) and good texture included heating at 65 ◦C for 30 min, pH 5.5, 0.06% CaCl2, and 10% buffalo milk. In addition, CM soft cheese quality was also determined according to lactation stage (Konuspayeva et al., 2014) and bovine chymosin (Chy-Max™) concen tration (Benkerroum et al., 2011), with corresponding optimal condi tions being 25 days postpartum and 1020 IMCU chymosin/L of milk.

Camel chymosin is not easily affordable as a coagulant in CM cheese making, especially for households and small-scale processors, due to its high cost and limited availability. Thus, alternative coagulants with cheaper prices and from easily accessible sources are encouraged. Using ginger crude extract to coagulate CM for cheese production is one alternative, due to the proteolytic activity of the protease enzymes in the extract, although the yield and quality of CM cheese produced from ginger crude extract are lower than those made from camel chymosin (Hailu et al., 2014). Organic acids were also effective coagulants for producing CM cheese. Mbye et al. (2020) reported that soft unripened cheeses prepared from citric acid (30% acid per litter of milk) had a higher yield and better sensory attributes than those prepared from camel chymosin.

Brined cheeses with salty, sour, and firm sensory descriptors are other types of cheese that can be successfully produced from CM (Hailu et al., 2018; Konuspayeva et al., 2017). After drainage, the curds are ripened in NaCl solution for several months to induce the development of flavour compounds in the cheese.

5.7. Yoghurt Similar to CM cheese, manufacturing CM yoghurt is quite difficult due to the poor coagulation ability of CM, which results in thin consis tency and weak product structure (Berhe et al., 2017). Texture is the most important attribute determining the appearance, mouthfeel, and overall consumer acceptability of yoghurt. However, the traditional approach to producing cow milk yoghurt is inapplicable to CM. Camel milk fermentation via starter cultures (S. thermophilus and L. delbruckii subsp. bulgaricus, 2.5%) and incubation at 37 ◦C up to 16–18 h did not form a desirable curd structure, but instead lead to fragile and hetero geneous dispersed flakes with watery texture (El Zubeir et al., 2012).

Most attempts to make CM yoghurt have extensively concentrated on increasing firmness and preventing syneresis of the product during processing and storage. Similar to producing CM cheese, mixing CM with other mammal milks, such as sheep milk (Ibrahem & El Zubeir,

2016), buffalo milk (Khalifa and Zakaria, 2019), and bovine milk (Kamal-Eldin et al., 2020), is a simple approach to making CM yoghurt.

However, mixing CM with other milk types reduces its inherent functionality, values, and properties, and therefore using single stabi liser and hydrocolloid or their combinations has been investigated to improve the consistency of CM yoghurt (Table 4). Al-Zoreky and Al- Otaibi (2015) reported that CM yoghurt containing 0.6% carbox ymethyl cellulose, gum acacia, or alginate with 0.06% CaCl2 had a thin and soft texture (semi-liquid). Adding either 2.5% bovine non-fat dry milk or 0.08% Na2EDTA did not result in a proper coagulum of CM yoghurt. In particular, the use of 0.6% of either pectin or carboxymethyl cellulose led to an unacceptable taste and flavour of the product.

Similarly, Hashim et al. (2009) reported that carboxymethyl cellulose at concentrations of 0.5–1.0% had no effect on the texture of CM yoghurt.

Kavas (2016) also reported an inability to produce yoghurt from CM added with bovine whey protein isolate (3%), samphire molasses (3%), and κ-carrageenan (0.1%). The interaction between κ-carrageenan and bovine whey protein isolate resulted in unacceptable properties (phys iochemical, rheological, microbiological, and sensory) of yoghurt.

However, these properties were significantly improved and highly accepted when κ-carrageenan was replaced by xanthan gum (0.5%) under the same processing conditions. Likewise, Mohsin et al. (2019) reported that adding 0.75% of biosynthesized xanthan from orange peels to CM date yoghurt markedly improved the texture, firmness, and sensory attributes of the product. Added biosynthesised xanthan resul ted in homogenous and compact microstructure with a dense network of casein micelles.

** : no data on concentration.

Table 4 A summary of studies concerning camel milk yoghurt using different stabilizers.

Type of yoghurt Gelation agents References Set-type yoghurt

• Stabilisers: CMC, pectin, gum acacia and alginate, 0.6% (w/v)

• Non-fat dry milk, 2.5% (w/v) • Na2EDTA, 0.08% (w/v)

• CaCl2, 0.06% (w/v) • Yogurt starters (S. salivarius ssp. thermophilus and L. delbrueckii ssp.

Bulgaricus), 2% (v/v) Al-Zoreky and Al-Otaibi (2015)

Set-type yoghurtFlavored yoghurt • Milk solid non-fat, 2.5–5.0% (w/v)

• Stabiliser (Grindstred ES255), 0.6–1.2% (w/v) • Yogurt culture (Yo-Fast-88)*

• Gelatin, CMC, alginate, 0.5–1.0% (w/v) • CaCl2, 0.05–0.1% (w/v)

• Flavoured with various fruits Hashim et al. (2009)

Set-type yoghurt • Arabic gum, 0–2% (w/w) • Yogurt starters (S. salivarius ssp. thermophilus and L. delbrueckii ssp.

Bulgaricus)** Jasim et al. (2018) Flavored yoghurt

• Gelatin, 1.2% (w/v) • Bovine skim milk powder, 5% (w/ v)

• CaCl2, 0.15% (v/v) • Maple strawberry maple syrup, 4% (v/v)

• Yogurt culture (YF-L811), 3% (v/v) Galeboe et al. (2018)

Set-type yoghurt • Modified starch, E1422, 1–5% • Yoghurt cultures (DVS-ABY-1 Nu- TRISH), 2%

Khalifa and Ibrahim (2015) Set-type yoghurt • Whey protein isolate, 3% (w/v)

• Samphire molasses, 3% (w/v) • κ-carrageenan, 0.1% (w/v)

• Xanthan gum, 0.05% (w/v) • Starter culture (Lb. bulgaricus and

Str. thermophilus), 3% (w/v) Kavas (2016) Set-type yoghurt

• Gelatin, 0–1.5% • Yoghurt cultures (Yo-Flex Express

1.0), 0.2% Mudgil et al. (2018) Stirred yoghurt • Polymerised whey protein isolates,

2–8% • Yogurt cultures** Sakandar et al. (2014) Set-type yoghurt

• Combined stabilizers: 0.5–1.5% (w/w) 1) Gelatin (E441) and mono- and diglyceride of fatty acid (E471) = 1:1

2) Guar gum (E412), sodium carboxymethyl cellulose (E466), and

E471 = 1:1:1 3) Modified starch (E1422) and E471 = 1:1

• Freeze dried ABY-1 culture, 2% Ibrahim and Khalifa (2015b)

* The level recommended by the dairy company (x), 1.5x, and 2x.

** : no data of concentration.

T.M. Ho et al.

Food Research International 153 (2022) 110870 11 Hashim et al. (2009) reported that the addition of either alginate or gelatin (0.5–1.0%) in combination with CaCl2 (0.05–0.1%) markedly improved the texture of CM yoghurt. Consumer testing indicated that

CM yoghurt containing 0.75% alginate and 0.075% CaCl2 had sensory properties and acceptability similar to that of cow milk yoghurt. Also, this formulation was successfully applied to CM yoghurt flavoured with various fruits. Similarly, Mudgil et al. (2018) reported that using gelatin at concentrations of 0.75–1.0% improved the texture, rheological properties, and appearance of CM yoghurt, and made them comparable to those of their commercial and cow milk counterparts. However, the sensory properties of CM yoghurt, taste and flavour in particular, were only mildly acceptable compared with cow milk yoghurt. Studying arabic gum (1–2%), Jasim et al. (2018) found that adding it led to increased viscosity, decreased syneresis, and enhanced texture and appearance, but high concentrations (~2%) of arabic gum led to an off- taste in CM yoghurt. Another formulation to produce maple strawberry syrup-flavoured CM yoghurt with acceptable quality was also reported by Galeboe et al. (2018) using 1.2% gelatin, 5.0% bovine skim milk powder, 0.15% CaCl2, 4.0% maple strawberry syrup, and 6% yoghurt culture (YF-L811), and by incubating the milk at 42 ◦C for 18 h.

Moreover, modified starch (E1422) at appropriate concentrations (e. g. 3%) was found to reduce syneresis, increase the water holding ca pacity, and improve chemical, sensory, and microstructural properties, with high overall acceptability of the product (Khalifa & Ibrahim, 2015).

However, using a mixture of this modified starch (E1422) and mono- and diglycerides at a 1:1 ratio (0.5–1.5%, w/w) for CM yoghurt pro duction was not preferred due to the ropy structure of the product, resulting in low sensory acceptance. Poor structure of CM yoghurt was also reported for the mixture of guar gum, sodium carboxymethyl cel lulose, and mono- and diglycerides at a ratio of 1:1:1. Nevertheless, at a concentration of 1.5% (w/w), the mixture of a 1:1 ratio of gelatin and mono- and diglycerides significantly stabilised the texture without affecting product flavour (Ibrahim & Khalifa, 2015).

Polymerised bovine whey protein is another stabiliser that has been investigated for use in CM yoghurt, and it was obtained through the heat treatment of whey protein solution (10%, pH 7) at 85 ◦C for 30 min (Sakandar et al., 2014). At a concentration of 8.0%, polymerised whey protein gave CM yoghurt desired characteristics in terms of texture and sensory properties. Furthermore, to enhance the therapeutical values of

CM yoghurt, several studies have investigated the addition of various herbal water extracts (Shori, 2013a, 2013b; Shori & Baba, 2012, 2014) and oat β-glucan (Ladjevardi et al., 2018). The aforementioned studies show that, although the production of CM yoghurt is achievable with desirable attributes for some formulation of stabilisers and hydrocol loids, utilising the products available on the market and acceptable by consumers is still complicated and requires further investigation. Rather than focusing on only choosing stabilisers and hydrocolloids, combining them with the alteration of CM properties, such as a reduction in fat global size (homogenisation and microfluidisation) and partially denaturising the proteins in CM (heat treatment) possibly warrant sub sequent studies.

6. Conclusion This review discussed the compositions, bioactive components, and functionalities of CM compared with bovine milk. High nutritional value, together with a lack of allergy-inducing β-lactoglobulin and a high content of β-casein, enables CM to be used as a daily drink for human consumption like bovine milk or to be converted into powder that can be incorporated into infant formula. However, preserving the functionalities of the bioactive components in CM during heat treatment or other processes is very challenging for food processors. In addition,

CM shows little tendency to coagulate primarily because of a lack of kappa-casein and β-lactoglobulin interactions, which causes many dif ficulties in the production of cheese, butter, and yoghurt from CM.

Deficiency of agglutinin (a protein promoting the clustering of fat globules), small fat globule size and strong fat and protein bonding are other hurdles in CM butter production. Despite the difficulties in pro cessing CM, studying and developing food products from CM remains an interesting topic, and several CM food products are being investigated and some are commercially available such as pasteurised CM, CM powder, cheese, butter, and yoghurt. However, improving the quality of these products to make their properties at least similar to their bovine milk counterparts requires further extensive investigation.

CRediT authorship contribution statement Thao M. Ho: Conceptualization, Methodology, Writing – original draft, Writing – review & editing, Visualization. Zhengzheng Zou:

Conceptualization, Methodology, Writing – original draft, Writing – review & editing, Visualization. Nidhi Bansal: Conceptualization,

Methodology, Writing – review & editing, Supervision.

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment The authors acknowledge the facilities, and the scientific and tech nical assistance, of the School of Agriculture and Food Sciences at The

University of Queensland.

References Abou-Soliman, N. H., Awad, S., & Desouky, M. M. (2020). Effect of digestive enzymes on the activity of camel-milk insulin. International Journal of Dairy Technology, 73(2),

341–344.

Abu-Lehia, I. H. (1989). Physical and chemical characteristics of camel milk fat and its fractions. Food Chemistry, 34(4), 261–271.

Abu-Tarboush, H. (1996). Comparison of associative growth and proteolytic activity of yogurt starters in whole milk from camels and cows. Journal of Dairy Science, 79(3),

366–371.

Agrawal, R. P., Budania, S., Sharma, P., Gupta, R., Kochar, D. K., Panwar, R. B., &

Sahani, M. S. (2007). Zero prevalence of diabetes in camel milk consuming Raica community of north-west Rajasthan. India. Diabetes Research and Clinical Practice, 76 (2), 290–296.

Agrawal, R. P., C. Swami, S., Beniwal, R., Kochar, D., S. Sahani, M., Tuteja, F., & K.

Ghouri, S. (2003). Effect of camel milk on glycemic control, risk factors and diabetes quality of life in type-1 diabetes: A randomised prospective controlled study. Journal of Camel Practice and Research, 10(1), 45-50.

Agrawal, R. P., Jain, S., Shah, S., Chopra, A., & Agarwal, V. (2011). Effect of camel milk on glycemic control and insulin requirement in patients with type 1 diabetes: 2-years randomized controlled trial. European Journal of Clinical Nutrition, 65(9), 1048.

Agrawal, R. P., Saran, S., Sharma, P., Gupta, R. P., Kochar, D. K., & Sahani, M. S. (2007).

Effect of camel milk on residual β-cell function in recent onset type 1 diabetes.

Diabetes Research and Clinical Practice, 77(3), 494–495.

Ahmed, A. S. M., & El Zubeir, I. E. M. (2015). Processing properties and chemical composition of low fat ice cream made from camel milk using natural additives.

International Journal of Dairy Science, 10(6), 297–305.

Ahmed, T., & Kanwal, R. (2004). Biochemical characteristics of lactic acid producing bacteria and preparation of camel milk cheese by using starter culture. Pakistan

Veterinary Journal, 24(2), 87–91.

Al-Ayadhi, L. Y., Halepoto, D. M., Al-Dress, A. M., Mitwali, Y., & Zainah, R. (2015).

Behavioral benefits of camel milk in subjects with autism spectrum disorder. Journal of the College of Physicians and Surgeons-Pakistan : JCPSP, 25(11), 819.

Al-Zoreky, N. S., & Al-Otaibi, M. M. (2015). Suitability of camel milk for making yogurt.

Food Science and Biotechnology, 24(2), 601–606.

Alhaj, O. A., Metwalli, A. A., & Ismail, E. A. (2011). Heat stability of camel milk proteins after sterilization process. Journal of Camel Practice and Research, 18(2), 277–282.

Asresie, A., Seifu, E., & Kurtu, M. Y. (2013). Churning efficiency and microbial quality of butter made from camel milk alone and blending it with goat milk. Net Journal of

Agricultural Science, 1(3), 75–80.

Atri, M. S., Saboury, A. A., Yousefi, R., Dalgalarrondo, M., Chobert, J.-M., Haertl´e, T., &

Moosavi-Movahedi, A. A. (2010). Comparative study on heat stability of camel and bovine apo and holo α-lactalbumin. Journal of Dairy Research, 77(1), 43–49.

Barłowska, J., Szwajkowska, M., Litwi´nczuk, Z., & Kr´ol, J. (2011). Nutritional value and technological suitability of milk from various animal species used for dairy production. Comprehensive Reviews in Food Science and Food Safety, 10(6), 291–302.

T.M. Ho et al.

Food Research International 153 (2022) 110870 12 Bekele, B., Hansen, E. B., Eshetu, M., Ipsen, R., & Hailu, Y. (2019). Effect of starter cultures on properties of soft white cheese made from camel (Camelus dromedarius) milk. Journal of Dairy Science, 102(2), 1108–1115.

Benabdelkamel, H., Masood, A., Alanazi, I. O., Alzahrani, D. A., Alrabiah, D. K.,

Alyahya, S. A., & Alfadda, A. A. (2017). Proteomic profiling comparing the effects of different heat treatments on camel (Camelus dromedarius) milk whey proteins.

International Journal of Molecular Sciences, 18(4), 721–735.

Benkerroum, N., Dehhaoui, M., El Fayq, A., & Tlaiha, R. (2011). The effect of concentration of chymosin on the yield and sensory properties of camel cheese and on its microbiological quality. International Journal of Dairy Technology, 64(2),

232–239.

Benkerroum, N., Mekkaoui, M., Bennani, N., & Hidane, K. (2004). Antimicrobial activity of camel’s milk against pathogenic strains of Escherichia coli and Listeria monocytogenes. International Journal of Dairy Technology, 57(1), 39–43.

Berhe, T., Seifu, E., Ipsen, R., Kurtu, M. Y., & Hansen, E. B. (2017). Processing challenges and opportunities of camel dairy products. International Journal of Food Science,

2017.

Berhe, T., Seifu, E., & Kurtu, M. Y. (2013). Physicochemical properties of butter made from camel milk. International Dairy Journal, 31(2), 51–54.

Cardoso, R. R. A., Santos, R. M. D. B., Cardoso, C. R. A., & Carvalho, M. O. (2010).

Consumption of camel’s milk by patients intolerant to lactose. A preliminary study.

Revista Alergia Mexico, 57, 26–32.

Dashe, D., Hansen, E. B., Kurtu, M. Y., Berhe, T., Eshetu, M., Hailu, Y., Waktola, A., &

Shegaw, A. (2020). Preservation of raw camel milk by lactoperoxidase system using hydrogen peroxide producing lactic acid bacteria. Open Journal of Animal Sciences,

10(03), 387–401.

Desouky, M. M., Salama, H. H., & El-Sayed, S. M. (2019). The effects of camel milk powder on the stability and quality properties of processed cheese sauce. Acta

Scientiarum Polonorum Technologia Alimentaria, 18(4), 349–359.

Dreiucker, J., & Vetter, W. (2011). Fatty acids patterns in camel, moose, cow and human milk as determined with GC/MS after silver ion solid phase extraction. Food

Chemistry, 126(2), 762–771.

Ejtahed, H. S., Niasari Naslaji, A., Mirmiran, P., Zraif Yeganeh, M., Hedayati, M.,

Azizi, F., & Moosavi Movahedi, A. (2015). Effect of camel milk on blood sugar and lipid profile of patients with type 2 diabetes: A pilot clinical trial. International

Journal of Endocrinology and Metabolism, 13(1), 1–6.

El-Agamy, E.-S.-I. (2006). Camel milk. In Y. W. Park, G. F. Haenlein, & W. L. Wendorff (Eds.), Handbook of Milk of Non-Bovine Mammals (pp. 409–480). West Sussex:

JohnWiley & Sons Ltd.

El-Agamy, E. I. (2007). The challenge of cow milk protein allergy. Small Ruminant

Research, 68(1), 64–72.

El-Agamy, E. I. (2009). Bioactive components in camel milk. In W. P. Young (Ed.),

Bioactive components in Milk and Dairy Products (pp. 159–192). Iowa: Wiley- Blackwell.

El-Agamy, E. I., Nawar, M., Shamsia, S. M., Awad, S., & Haenlein, G. F. W. (2009). Are camel milk proteins convenient to the nutrition of cow milk allergic children? Small

Ruminant Research, 82(1), 1–6.

El-Agamy, E. I., Ruppanner, R., Ismail, A., Champagne, C. P., & Assaf, R. (1996).

Purification and characterization of lactoferrin, lactoperoxidase, lysozyme and immunoglobulins from camel’s milk. International Dairy Journal, 6(2), 129–145.

El-Zeini, H. M. (2006). Microstructure, rheological and geometrical properties of fat globules of milk from different animal species. Polish Journal of Food and Nutrition

Sciences, 15(2), 147–153.

El Agamy, E. S. I., & Ruppanneb, R. (1992). Antibacterial and antiviral activity of camel milk protective proteins. Journal of Dairy Research, 59(2), 169–175.

El Zubeir, I., Basher, M., Alameen, M., Mohammed, M., & Shuiep, E. (2012). The processing properties, chemical characteristics and acceptability of yoghurt made from non bovine milks. Livestock Research for Rural Development, 24(3), 1–11.

El Zubeir, I. E., & Jabreel, S. O. (2008). Fresh cheese from camel milk coagulated with

Camifloc. International Journal of Dairy Technology, 61(1), 90–95.

Elagamy, E. I. (2000). Effect of heat treatment on camel milk proteins with respect to antimicrobial factors: A comparison with cows’ and buffalo milk proteins. Food

Chemistry, 68(2), 227–232.

Ereifej, K. I., Alu’datt, M. H., Alkhalidy, H. A., Alli, I., & Rababah, T. (2011). Comparison and characterisation of fat and protein composition for camel milk from eight

Jordanian locations. Food Chemistry, 127(1), 282-289.

FAO, Food and Agriculture Organization of the United Nations. (2019). FAOSTAT database. FAO, Rome, Italy. http://www.fao.org/faostat/en/#home.

Farah, Z. (1986). Effect of heat treatment on whey proteins of camel milk.

Milchwissenschaft, 41, 763–765.

Farah, Z. (1993). Composition and characteristics of camel milk. Journal of Dairy

Research, 60(4), 603–626.

Farah, Z., & Atkins, D. (1992). Heat coagulation of camel milk. Journal of Dairy Research,

59(2), 229–231.

Farah, Z., & Fischer, A. (2004). Milk and Meat From the Camel: Handbook on Products and

Processing. Zürich/Singen: vdf Hochschulverlag AG an der ETH Zentrum.

Farah, Z., Rettenmaier, R., & Atkins, D. (1992). Vitamin content of camel milk.

International Journal for Vitamin and Nutrition Research, 62(1), 30–33.

Farah, Z., & Rüegg, M. (1991). The creaming properties and size distribution of fat globules in camel milk. Journal of Dairy Science, 74(9), 2901–2904.

Farah, Z., Streiff, T., & Bachmann, M. (1989). Manufacture and characterization of camel milk butter. Milchwissenschaft, 44(7), 412–414.

Faraz, A., Mustafa, M. I., Lateef, M., Yaqoob, M., & Younas, M. (2013). Production potential of camel and its prospects in Pakistan. Punjab University Journal of Zoolog,

28, 89–95.

Faye, B. (2015). Role, distribution and perspective of camel breeding in the third millennium economies. Emirates Journal of Food and Agriculture, 27(4), 318–327.

Faye, B., Konuspayeva, G., & Bengoumi, M. (2019). Vitamins of camel milk: A comprehensive review. Journal of Camelid Science, 12, 17–32.

Felfoul, I., Jardin, J., Gaucheron, F., Attia, H., & Ayadi, M. A. (2017). Proteomic profiling of camel and cow milk proteins under heat treatment. Food Chemistry, 216, 161–169.

Felfoul, I., Lopez, C., Gaucheron, F., Attia, H., & Ayadi, M. (2015). Fouling behavior of camel and cow milks under different heat treatments. Food and Bioprocess

Technology, 8(8), 1771–1778.

Fuquay, J. W., McSweeney, P. L., & Fox, P. F. (2011). Encyclopedia of dairy sciences.

London: Elsevier.

Galeboe, O., Seifu, E., & Sekwati-Monang, B. (2018). Production of camel milk yoghurt: physicochemical and microbiological quality and consumer acceptability.

International Journal of Food Studies, 7(2), 51–63.

Genene, A., Hansen, E. B., Eshetu, M., Hailu, Y., & Ipsen, R. (2019). Effect of heat treatment on denaturation of whey protein and resultant rennetability of camel milk.

LWT, 101, 404–409.

Goff, H. D., & Hartel, R. W. (2013). Ice cream. New York: Springer Science & Business

Media.

Habtegebriel, H., Edward, D., Wawire, M., Sila, D., & Seifu, E. (2018). Effect of operating parameters on the surface and physico-chemical properties of spray-dried camel milk powders. Food and Bioproducts Processing, 112, 137–149.

Habtegebriel, H., Wawire, M., & Sila, D. (2018). The effect of pretreatment (spray drying) on the yield and selected nutritional components of whole camel milk powder.

Journal of Food Science, 83(12), 2983–2991.

Haddadin, M. S. Y., Gammoh, S. I., & Robinson, R. K. (2008). Seasonal variations in the chemical composition of camel milk in Jordan. Journal of Dairy Research, 75(1),

8–12.

Hailu, Y., Hansen, E. B., Seifu, E., Eshetu, M., Petersen, M. A., Lametsch, R., … Ipsen, R. (2018). Rheological and sensory properties and aroma compounds formed during ripening of soft brined cheese made from camel milk. International Dairy Journal, 81,

122–130.

Hailu, Y., Seifu, E., & Yilma, Z. (2014). Physicochemical properties and consumer acceptability of soft unripened cheese made from camel milk using crude extract of ginger (Zingiber officinale) as coagulant. African Journal of Food Science, 8(2), 87–91.

Hajian, N., Salami, M., Mohammadian, M., Moghadam, M., & Emam-Djomeh, Z. (2020).

Production of low-fat camel milk functional ice creams fortified with camel milk casein and its antioxidant hydrolysates. Applied Food Biotechnology, 7(2), 95–102.

Hamers-Casterman, C., Atarhouch, T., Muyldermans, S., Robinson, G., Hammers, C.,

Songa, E. B., & Hammers, R. (1993). Naturally occurring antibodies devoid of light chains. Nature, 363(6428), 446.

Hashim, I., Khalil, A., & Habib, H. (2009). Quality and acceptability of a set-type yogurt made from camel milk. Journal of Dairy Science, 92(3), 857–862.

Hassan, S. M. I. (2009). Production of ice-cream from camel milk. Sudan University of

Science and Technology.

Hinz, K., Connor, P. M., Huppertz, T., Ross, R. P., & Kelly, A. L. (2012). Comparison of the principal proteins in bovine, caprine, buffalo, equine and camel milk. Journal of

Dairy Research, 79(2), 185–191.

Ho, T. M., Chan, S., Yago, A. J., Shravya, R., Bhandari, B. R., & Bansal, N. (2019).

Changes in physicochemical properties of spray-dried camel milk powder over accelerated storage. Food Chemistry, 295, 224–233.

Ho, M. T., Zou, Z., Bhandari, B., & Bansal, N. (2020). Properties of functional camel milk powder. In Drying in the Dairy Industry-From Established Technologies to Advanced

Innovations (pp. 226–240). Boca Raton, FL: CRC Press, Taylor and Francis Group.

Ho, T. M., Ton, T. T., Gaiani, C., Bhandari, B. R., & Bansal, N. (2021). Changes in surface chemical composition relating to rehydration properties of spray-dried camel milk powder during accelerated storage. Food Chemistry, Article 130136.

Ibrahem, S. A., & El Zubeir, I. E. (2016). Processing, composition and sensory characteristic of yoghurt made from camel milk and camel–sheep milk mixtures.

Small Ruminant Research, 136, 109–112.

Ibrahim, A., & Khalifa, S. (2015). Effect of freeze-drying on camel’s milk nutritional properties. International Food Research Journal, 22(4), 1438–1445.

Ibrahim, A. H., & Khalifa, S. A. (2015). The effects of various stabilizers on physiochemical properties of camel’s milk yoghurt. Journal of American Science, 11 (1), 15–24.

Inayat, S., Arain, M., Khaskheli, M., & Farooq, A. (2007). Study on the production and quality improvement of soft unripened cheese made from buffalo milk as compared with camel milk. Italian Journal of Animal Science, 6(sup2), 1115–1119.

Ipsen, R. (2017). Opportunities for producing dairy products from camel milk: A comparison with bovine milk. East African Journal of Sciences, 11(2), 93–98.

Jafarpour, A. (2017). Feasibility of manufacture and investigation of physicochemical properties of camel milk–based ice cream. Journal of Scientific Agriculture, 300–302.

Jasim, M. A., Salih, G. M., & Hamk, M. L. (2018). The effect of arabic gum on physicochemical and sensory properties of camel milk, yogurt. In Journal of Zankoy

Sulaimani (Special Issue, 2nd Internationl Conference of Agricultural Sciences) (pp. 1–9).

Kamal-Eldin, A., Alhammadi, A., Gharsallaoui, A., Hamed, F., & Ghnimi, S. (2020).

Physicochemical, rheological, and micro-structural properties of yogurts produced from mixtures of camel and bovine milks. NFS Journal, 19, 26–33.

Kappeler, S. R. (1998). Compositional and structural analysisof camel milk proteins with emphasis on protective proteins. ETH, Zurich, Switzerland: Swiss Federal Institute of

Technology. Ph.D. Thesis.

Kappeler, S. R., Farah, Z., & Puhan, Z. (2003). 5’-Flanking regions of camel milk genes are highly similar to homologue regions of other species and can be divided into two distinct groups. Journal of Dairy Science, 86(2), 498–508.

Kavas, N. (2016). Yoghurt production from camel (Camelus dramedarius) milk fortified with samphire molasses and different colloids. Mljekarstvo/Dairy, 66(1), 34–47.

T.M. Ho et al.

Food Research International 153 (2022) 110870 13 Khalifa, S. A., & Ibrahim, A. H. (2015). Influence of addition modified starches as stabilizer on physicochemical and textural properties of camel milk yoghurt. Zagazig

Journal of Agricultural Research, 42(2), 295–307.

Khalifa, M. I., & Zakaria, A. M. (2019). Physiochemical, sensory characteristics and acceptability of a new set yogurt developed from camel and goat milk mixed with buffalo milk. Animal and Veterinary Sciences, 7(3), 172–177.

Khan, H. A. I. D. E. R., Athar, I. H., & Aslam, M. U. H. A. M. M. A. D. (2004). Evaluation of cheese prepared by processing camel milk. Pakistan Journal of Zoology, 36(4),

323–326.

Konuspayeva, G., Camier, B., Aleilawi, N., Al-Shumeimyri, M., Al-Hammad, K.,

Algruin, K., … Faye, B. (2017). Manufacture of dry-and brine-salted soft camel cheeses for the camel dairy industry. International Journal of Dairy Technology, 70(1),

92–101.

Konuspayeva, G., Camier, B., Gaucheron, F., & Faye, B. (2014). Some parameters to process camel milk into cheese. Emirates Journal of Food and Agriculture, 26(4),

354–358.

Konuspayeva, G., Faye, B., & Loiseau, G. (2009). The composition of camel milk: A meta- analysis of the literature data. Journal of Food Composition and Analysis, 22(2),

95–101.

Konuspayeva, G., Baubekova, A., Akhmetsadykova, S., Akhmetasdykov, N., & Faye, B. (2019). Concentrations in D-and L-lactate in raw cow and camel milk. Journal of

Camel Practice and Research, 26(1), 111–113.

Konuspayeva, G., & Faye, B. (2021). Recent advances in camel milk processing. Animals,

11(4), 1045.

Konuspayeva, G. S. (2020a). Manufacture and Challenges of Camel Milk Cheese. In

O. A. Alhaj, B. Faye, & R. P. Agrawal (Eds.), Health and Environmental Benefits of

Camel Products (pp. 110–122). Hershey, USA: IGI Global.

Konuspayeva, G. S. (2020b). Camel Milk Composition and Nutritional Value. In

O. A. Alhaj, B. Faye, & R. P. Agrawal (Eds.), Health and Environmental Benefits of

Camel Products (pp. 15–40). Hershey, USA: IGI Global.

Konuspayeva, G., Faye, B., & Duteurtre, G. (2021). Commerce en ligne du lait de chamelle: Nouveaux acteurs, nouveaux march´es. Revue d’´elevage et de m´edecine v´et´erinaire des pays tropicaux, 74(3), 137–144.

Korish, A. A., Abdel Gader, A. G., Korashy, H. M., Al-Drees, A. M., Alhaider, A. A., &

Arafah, M. M. (2015). Camel milk attenuates the biochemical and morphological features of diabetic nephropathy: Inhibition of Smad1 and collagen type IV synthesis.

Chemico-Biological Interactions, 229, 100–108.

Kula, J. T., & Tegegne, D. (2016). Chemical composition and medicinal values of camel milk. International Journal of Research Studies in Biosciences, 4(4), 13–25.

Ladjevardi, Z. S., Yarmand, M. S., Emam-Djomeh, Z., & Niasari-Naslaji, A. (2018).

Physicochemical properties and viability of probiotic bacteria of functional synbiotic camel yogurt affected by oat β-glucan during storage. Journal of Agricultural Science and Technology A, 18(5), 1233–1246.

Lajnaf, R., Picart-Palmade, L., Attia, H., Marchesseau, S., & Ayadi, M. A. (2017). The effect of pH and heat treatments on the foaming properties of purified α-lactalbumin from camel milk. Colloids and Surfaces B: Biointerfaces, 156, 55–61.

Lajnaf, R., Picart-Palmade, L., Cases, E., Attia, H., Marchesseau, S., & Ayadi, M. (2018).

The foaming properties of camel and bovine whey: The impact of pH and heat treatment. Food Chemistry, 240, 295–303.

Lajnaf, R., Zouari, A., Trigui, I., Attia, H., & Ayadi, M. A. (2020). Effect of different heating temperatures on foaming properties of camel milk proteins: A comparison with bovine milk proteins. International Dairy Journal, 104, Article 104643.

Laleye, L., Jobe, B., & Wasesa, A. (2008). Comparative study on heat stability and functionality of camel and bovine milk whey proteins. Journal of Dairy Science, 91 (12), 4527–4534.

Lam, R. S. H., & Nickerson, M. T. (2015). The effect of pH and temperature pre- treatments on the structure, surface characteristics and emulsifying properties of alpha-lactalbumin. Food Chemistry, 173, 163–170.

Li, R., Yue, H., Shi, Z., Shen, T., Yao, H., Zhang, J., … Yang, J. (2020). Protein profile of whole camel milk resulting from commercial thermal treatment. LWT, 134, Article

110256.

Limon, A., Gallegos-Perez, J.-L., Reyes-Ruiz, J. M., Aljohi, M. A., Alshanqeeti, A. S., &

Miledi, R. (2014). The endogenous GABA bioactivity of camel, bovine, goat and human milks. Food Chemistry, 145, 481–487.

Maghraby, A. S., Mohamed, M. A., & Abdel-Salam, A. M. (2005). Anti-schistosomal activity of colostral and mature camel milk on Schistosoma mansoni infected mice.

Asia Pacific Journal of Clinical Nutrition, 14(4), 432.

Mal, G., Dande, S. S., Jain, V. K., & Sahani, M. S. (2006). Therapeutic value of camel milk as a nutritional supplement for multiple drug resistant (MDR) tuberculosis patients.

Israel Journal of Veterinary Medicine, 61, 88–91.

Mal, G., Sena, D. S., Jain, V. K., Singhvi, N. M., & Sahani, M. S. (2000). Role of camel milk as an adjuvant nutritional supplement in human tuberculosis patients. Livestock

International, 4(4), 7–14.

Malik, A., Al-Senaidy, A., Skrzypczak-Jankun, E., & Jankun, J. (2012). A study of the anti-diabetic agents of camel milk. International Journal of Molecular Medicine, 30(3),

585–592.

Mati, A., Senoussi-Ghezali, C., Si Ahmed Zennia, S., Almi-Sebbane, D., El-Hatmi, H., &

Girardet, J.-M. (2017). Dromedary camel milk proteins, a source of peptides having biological activities – A review. International Dairy Journal, 73, 25-37.

Maurad, K., & Meriem, K. H. (2008). Probiotic characteristics of Lactobacillus plantarum strains from traditional butter made from camel milk in arid regions (Sahara) of

Algeria. Grasas y Aceites, 59(3), 218–224.

Mbye, M., Sobti, B., Al Nuami, M. K., Al Shamsi, Y., Al Khateri, L., Al Saedi, R., … Kamal- Eldin, A. (2020). Physicochemical properties, sensory quality, and coagulation behavior of camel versus bovine milk soft unripened cheeses. NFS Journal, 20,

28–36.

Mehaia, M. A. (1993). Fresh soft white cheese (Domiati-Type) from camel milk:

Composition, yield, and sensory evaluation. Journal of Dairy Science, 76(10),

2845–2855.

Mehaia, M. A. (2006). Manufacture of fresh soft white cheese (Domiati type) from dromedary camel’s milk using ultrafiltration process. Journal of Food Technology, 4 (3), 206–212.

Minervini, F., Algaron, F., Rizzello, C. G., Fox, P. F., Monnet, V., & Gobbetti, M. (2003).

Angiotensin I-converting-enzyme-inhibitory and antibacterial peptides from lactobacillus helveticus pr4 proteinase-hydrolyzed caseins of milk from six species.

Applied and Environmental Microbiology, 69(9), 5297.

Mohamad, R. H., Zekry, Z. K., Al-Mehdar, H. A., Salama, O., El-Shaieb, S. E., El- Basmy, A. A., … Sharawy, S. M. (2009). Camel milk as an adjuvant therapy for the treatment of type 1 diabetes: Verification of a traditional ethnomedical practice.

Journal of Medicinal Food, 12(2), 461–465.

Mohamed, A. E., Babiker, I. A., & Mohamed, T. E. (2013). Preparation of fresh soft cheese from dromedary camel milk using acid and heat method. Research Opinions in Animal and Veterinary Sciences, 3(9), 289–292.

Mohsin, A., Ni, H., Luo, Y., Wei, Y., Tian, X., Guan, W., Ali, M., Khan, I. M., Niazi, S.,

Rehman, S. U., & Zhuang, Y. (2019). Qualitative improvement of camel milk date yoghurt by addition of biosynthesized xanthan from orange waste. LWT, 108, 61–68.

Mourad, K., & Nour-Eddine, K. (2006). Physicochemical and microbiological study of

“shmen”, a traditional butter made from camel milk in the Sahara (Algeria): Isolation and identification of lactic acid bacteria and yeasts. Grasas y Aceites, 57(2), 198–204.

Mudgil, P., Jumah, B., Ahmad, M., Hamed, F., & Maqsood, S. (2018). Rheological, micro- structural and sensorial properties of camel milk yogurt as influenced by gelatin.

LWT, 98, 646–653.

Muyldermans, S., Cambillau, C., & Wyns, L. (2001). Recognition of antigens by single- domain antibody fragments: The superfluous luxury of paired domains. Trends in

Biochemical Sciences, 26(4), 230–235.

Ogolla, J. A., Kulig, B., Badulescu, L., Okoth, M. W., Esper, G., Breitenbach, J., …

Sturm, B. (2019). Influence of inlet drying air temperature and milk flow rate on the physical, optical and thermal properties of spray-dried camel milk powders. Food and

Bioprocess Technology, 12(5), 751–768.

Omar, A., Harbourne, N., & Oruna-Concha, M. J. (2016). Quantification of major camel milk proteins by capillary electrophoresis. International Dairy Journal, 58, 31–35.

Omar, A., Harbourne, N., & Oruna-Concha, M. J. (2018). Effects of industrial processing methods on camel skimmed milk properties. International Dairy Journal, 84, 15–22.

Ortega-Rivas, E., Juliano, P., & Yan, H. (2005). Food powders: Physical Properties,

Processing, and Functionality. new York: Springer Science & Business Media.

Othman, A. (2016). Detection of bactericidal activity of camel’s milk compared with raw and processed cow’s milk against pathogenic bacteria. Egyptian Pharmaceutical

Journal, 15(1), 31–37.

Qadeer, Z., Huma, N., Sameen, A., & Iqbal, T. (2015). Camel milk cheese: Optimization of processing conditions. Journal of Camelid Science, 8, 18–25.

Quan, S., Tsuda, H., & Miyamoto, T. (2008). Angiotensin I-converting enzyme inhibitory peptides in skim milk fermented with Lactobacillus helveticus 130B4 from camel milk in Inner Mongolia, China. Journal of the Science of Food and Agriculture, 88(15),

2688–2692.

Ramet, J. P. (2001). The technology of making cheese from camel milk (Camelus dromedarius). Rome: Food and Agriculture Organization of the United Nations.

Redwan, E., & Tabll, A. (2007). Camel lactoferrin markedly inhibits hepatitis c virus genotype 4 infection of human peripheral blood leukocytes. Journal of Immunoassay and Immunochemistry, 28(3), 267–277.

Riechmann, L., & Muyldermans, S. (1999). Single domain antibodies: Comparison of camel VH and camelised human VH domains. Journal of Immunological Methods, 231 (1), 25–38.

Roy, I., Bhushani, A., & Anandharamakrishnan, C. (2017). Techniques for the

Preconcentration of Milk. In C. Anandharamakrishnan (Ed.), Handbook of Drying for

Dairy Products (pp. 23–37). Chennai: JohnWiley & Sons.

Saadi, A. M., Ali, F. F., & Jasim, A. Y. (2019). Study of the soft cheese composition produced from a mixture of sheep and camel milk at different storage periods using the enzyme trypsin and calcium chloride. Annals of Agri Bio Research, 24, 316–320.

Saalfeld, W., & Edwards, G. (2010). Distribution and abundance of the feral camel (Camelus dromedarius) in Australia. The Rangeland Journal, 32(1), 1–9.

Sakandar, H. A., Imran, M., Huma, N., Ahmad, S., Aslam, H. K. W., Azam, M., &

Shoaib, M. (2014). Effects of polymerized whey proteins isolates on the quality of stirred yoghurt made from camel milk. Journal of Food Processing & Technology, 5(7),

1–5.

Salami, M., Moosavi-Movahedi, A., Ehsani, M., Yousefi, R., Haertl´e, T., Jean-Marc

Chobert, J. M., … Niasari-Naslaji, A. (2010). Improvement of the antimicrobial and antioxidant activities of camel and bovine whey proteins by limited proteolysis.

Journal of Agricultural and Food Chemistry, 58(6), 3297–3302.

Salem, S. A., Meead, G. H., El-Rashody, & Fardous, M. M. (2017). Physicochemical and sensory properties of ice cream made from camel milk and fortified with dates products. BEST: International Journal of Humanities, Arts, Medicine and Sciences, 5(1),

29–40.

Sawaya, W. N., Khalil, J. K., Al-Shalhat, A., & Al-Mohammad, H. (1984). Chemical composition and nutritional quality of camel milk. Journal of Food Science, 49(3),

744–747.

Sboui, A., Khorchani, T., Djegham, M., Agrebi, A., Elhatmi, H., & Belhadj, O. (2010).

Anti-diabetic effect of camel milk in alloxan-induced diabetic dogs: A dose–response experiment. Journal of Animal Physiology and Animal Nutrition, 94(4), 540–546.

Sela, S., Pinto, R., Merin, U., & Rosen, B. (2003). Thermal inactivation of Escherichia coli in camel milk. Journal of Food Protection, 66(9), 1708–1711.

Shabo, Y., Barzel, R., & Yagil, R. (2008). Etiology of Crohn’s disease and camel milk treatment. Journal of Camel Practice and Research, 15(1), 55–59.

T.M. Ho et al.

Food Research International 153 (2022) 110870 14 Shabo, Y., & Yagil, R. (2005). Etiology of autism and camel milk as therapy. International

Journal on Disability and Human Development, 4(2), 67–70.

Shabo, Y., Yagil, R., Barzel, R., & Margoulis, M. (2005). Camel milk for food allergies in children. Israel Medical Association Journal, 7(12), 796–798.

Shahein, M., Hassanein, A., & Zayan, A. F. (2014). Evaluation of soft cheese manufactured from camel and buffalo milk. World Journal Dairy Food Sciences, 9,

213–219.

Shori, A. B. (2013a). Antioxidant activity and viability of lactic acid bacteria in soybean- yogurt made from cow and camel milk. Journal of Taibah University for Science, 7(4),

202–208.

Shori, A. B. (2013b). Nutritional and therapeutical values of chickpea water extract enriched yogurt made from cow and camel milk. American Journal of Drug Discovery and Development, 3(2), 47–59.

Shori, A. B. (2015). Camel milk as a potential therapy for controlling diabetes and its complications: A review of in vivo studies. Journal of food and drug analysis, 23(4),

609–618.

Shori, A. B., & Baba, A. S. (2012). Viability of lactic acid bacteria and sensory evaluation in Cinnamomum verum and Allium sativum-bio-yogurts made from camel and cow milk. Journal of the Association of Arab Universities for Basic and Applied Sciences, 11 (1), 50–55.

Shori, A. B., & Baba, A. S. (2014). Comparative antioxidant activity, proteolysis and in vitro α-amylase and α-glucosidase inhibition of Allium sativum-yogurts made from cow and camel milk. Journal of Saudi Chemical Society, 18(5), 456–463.

Shyam, P. S., Bhavbhuti, M. M., Wadhwani, K. N., Darji, V. B., & Aparnathi, K. D. (2016).

Evaluation of camel milk for selected processing related parameters and comparisons with cow and buffalo milk. International Journal of Health, 3(1), 27–37.

Smiddy, M. A., Huppertz, T., & van Ruth, S. M. (2012). Triacylglycerol and melting profiles of milk fat from several species. International Dairy Journal, 24(2), 64–69.

Soleymanzadeh, N., Mirdamadi, S., Mirzaei, M., & Kianirad, M. (2019). Novel β-casein derived antioxidant and ACE-inhibitory active peptide from camel milk fermented by Leuconostoc lactis PTCC1899: Identification and molecular docking. International

Dairy Journal, 97, 201–208.

Soliman, G. Z. A. (2005). Comparison of chemical and mineral content of milk from human, cow, buffalo, camel and goat in egypt. The Egyptian Journal of Hospital

Medicine, 21, 116–130.

Stahl, T., Sallmann, H. P., Duehlmeier, R., & Wernery, U. (2006). Selected vitamins and fatty acid patterns in dromedary milk and colostrums. Journal of Camel Practice and

Research, 13, 53–57.

Sulieman, A., Elamin, O. M., Elkhalifa, E. A., & Laleye, L. (2018). A comparative study of physicochemical properties of freeze-dried camel’s milk and cow’s milk powder.

Discourse J. Agric. Food Sci, 6(2), 11–16.

Sulieman, A. M. E., Elamin, O. M., Elkhalifa, E. A., & Laleye, L. (2014). Comparison of physicochemical properties of spray-dried camel’s milk and cow’s milk powder.

International Journal of Food Science and Nutrition Engineering, 4(1), 15–19.

Tagliazucchi, D., Shamsia, S., & Conte, A. (2016). Release of angiotensin converting enzyme-inhibitory peptides during in vitro gastro-intestinal digestion of camel milk.

International Dairy Journal, 56, 119–128.

Tantawy, E., El-Sayed, G. R., & El-Said, E.-S.-E.-S. (2010). Effect of camel milk on oxidative stresses in experimentally induced diabetic rabbits. Veterinary Research

Forum, 1(1), 30–43.

Tayefi-Nasrabadi, H., Hoseinpour-Fayzi, M. A., & Mohasseli, M. (2011). Effect of heat treatment on lactoperoxidase activity in camel milk: A comparison with bovine lactoperoxidase. Small Ruminant Research, 99(2–3), 187–190.

Tomotake, H., Okuyama, R., Katagiri, M., Fuzita, M., Yamato, M., & Ota, F. (2006).

Comparison between Holstein cow’s milk and Japanese-Saanen goat’s milk in fatty acid composition, lipid digestibility and protein profile. Bioscience, Biotechnology, and

Biochemistry, 70(11), 2771–2774.

Yadav, A. K., Kumar, R., Priyadarshini, L., & Singh, J. (2015). Composition and medicinal properties of camel milk: A Review. Asian Journal of Dairy and Food Research, 34(2),

83–91.

Yirda, A., Eshetu, M., & Babege, K. (2020). Current Status of Camel Dairy Processing and

Technologies: A Review. Open Journal of Animal Sciences, 10(3), 362–377.

Yagil, R., & Etzion, Z. (1980). Effect of drought condition on the quality of camel milk.

Journal of Dairy Research, 47(2), 159–166.

Yagil, R., Zagorski, O., Van Creveld, C., & Saran, A. (1994). Science and camel’s milk production. In G. Saint Marin (Ed.), Actes du Colloque: Dromadaires et chameaux animaux laitier (pp. 75–89). Paris: Expansion Scientifique Francais.

Zhang, L., Boeren, S., Smits, M., van Hooijdonk, T., Vervoort, J., & Hettinga, K. (2016).

Proteomic study on the stability of proteins in bovine, camel, and caprine milk sera after processing. Food Research International, 82, 104–111.

Ziane, M., Couvert, O., Le Chevalier, P., Moussa-Boudjemaa, B., & Leguerinel, I. (2016).

Identification and characterization of aerobic spore forming bacteria isolated from commercial camel’s milk in south of Algeria. Small Ruminant Research, 137, 59–64.

Zouari, A., Briard-Bion, V., Schuck, P., Gaucheron, F., Delaplace, G., Attia, H., &

Ayadi, M. A. (2020). Changes in physical and biochemical properties of spray dried camel and bovine milk powders. LWT, Article 109437.

Zouari, A., Perrone, ´I. T., Schuck, P., Gaucheron, F., Dolivet, A., Attia, H., & Ayadi, M. A. (2018). Effect of outlet drying temperature and milk fat content on the physicochemical characteristics of spray-dried camel milk powder. Drying

Technology, 1–10.

Zouari, A., Schuck, P., Gaucheron, F., Triki, M., Delaplace, G., Gauzelin-Gaiani, C., …

Ayadi, M. A. (2020a). Microstructure and chemical composition of camel and cow milk powders’ surface. LWT, 117, Article 108693.

Zouari, A., Briard-Bion, V., Schuck, P., Gaucheron, F., Delaplace, G., Attia, H., &

Ayadi, M. A. (2020b). Changes in physical and biochemical properties of spray dried camel and bovine milk powders. LWT, Article 109437.

Zouari, A., Mtibaa, I., Triki, M., Jridi, M., Zidi, D., Attia, H., & Ayadi, M. A. (2020c).

Effect of spray-drying parameters on the solubility and the bulk density of camel milk powder: A response surface methodology approach. International Journal of

Dairy Technology, 73(3), 616–624.

Ziaeifar, L., Shahi, M. L. M., Salami, M., & Askari, G. R. (2018). Effect of casein and inulin addition on physico-chemical characteristics of low fat camel dairy cream.

International Journal of Biological Macromolecules, 117, 858–862.

Zou, Z., Bauland, J., Hewavitharana, A. K., Al-Shehri, S.a. S., Duley, J. A., Cowley, D. M.,

… Bansal, N. (2021a). A sensitive, high-throughput fluorescent method for the determination of lactoperoxidase activities in milk and comparison in human, bovine, goat and camel milk.“. Food Chemistry, 339, Article p128090.

Zou, Z., Bouchereau-De Pury, C., Hewavitharana, A. K., Al-Shehri, S. S., Duley, J. A.,

Cowley, D. M., … Bansal, N. (2021b). A sensitive and high-throughput fluorescent method for determination of oxidase activities in human, bovine, goat and camel milk. Food Chemistry, 336, Article 127689.

T.M. Ho et al.

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综述骆驼奶：营养价值、热稳定性及潜在食品产品的综述

Thao M. Ho a,b,*, Zhengzheng Zou b, Nidhi Bansal b,* a 赫尔辛基大学食品与营养系，芬兰赫尔辛基，P.O. Box 66, 00014 b 昆士兰大学农业与食品科学学院，澳大利亚布里斯班，QLD 4072

**A R T I C L E I N F O** 关键词：骆驼奶热处理生物活性化合物骆驼奶制品

**A B S T R A C T** 骆驼奶在营养价值方面优于牛乳，且与人乳非常接近。它含有高浓度的多种对人体健康至关重要的生物活性化合物。尽管具有显著的营养和健康益处，但与牛乳相比，以骆驼奶为原料生产的食品仍然非常有限。牛乳和骆驼奶在成分上的差异使得适用于牛乳产品的生产工艺无法直接用于骆驼奶产品。因此，全面了解骆驼奶的组成、生物活性成分及其热稳定性，对于在保持其固有营养价值的同时实现最终产品的理想品质至关重要。本综述描述了骆驼奶中宏量营养素（尤其是蛋白质）的特性与功能，以及骆驼奶的热稳定性。此外，还全面讨论了多种骆驼奶产品（包括巴氏奶/灭菌奶、发泡剂、奶粉、冰淇淋、奶酪、黄油和酸奶）生产中的技术问题、生产难点以及提升产品质量的未来研究方向。

**1. 引言** 炎热气候、水资源稀缺和牧草匮乏是骆驼偏好的环境条件。因此，骆驼通常饲养在拥有大面积沙漠的国家，并可用于多种用途，如产奶、肉用、毛用、运输、赛驼、旅游、农耕和化妆品原料（Faye, 2015; Saalfeld & Edwards, 2010）。在产奶方面，根据联合国粮农组织（FAO, 2019）数据，非洲国家（如索马里、苏丹、尼日利亚、肯尼亚、乍得、毛里塔尼亚、埃塞俄比亚和马里）约占全球新鲜全脂骆驼奶（CM）产量的90%，其次是亚洲国家（如印度、也门、沙特阿拉伯、阿拉伯联合酋长国、中国和阿富汗）。骆驼奶的营养价值优于牛乳，且与人乳高度相似，因此在获取人乳受限的情况下，骆驼奶被视为人乳的优良替代品。骆驼奶含有满足人体膳食需求的均衡必需氨基酸比例，富含易水解的β-酪蛋白，且不含致敏性的β-乳球蛋白（El-Agamy, 2009; Hinz et al., 2012; Kappeler et al., 2003）。此外，骆驼奶富含维生素和矿物质，以及多种具有抗癌、抗糖尿病和抗菌特性的保护性蛋白（如免疫球蛋白、乳铁蛋白、溶菌酶和乳过氧化物酶）（Barłowska et al., 2011; Konuspayeva et al., 2009; Zou et al., 2021a, 2021b）。

尽管骆驼奶营养价值极高，但其全球供应量及以骆驼奶为原料的食品产品仍然非常有限。目前对骆驼奶的利用远未达到其潜力。骆驼奶产品的生产极具挑战性，但在过去十年中，已有许多研究致力于优化加工条件，以生产保质期长、品质优良的骆驼奶产品，这对于实现骆驼奶的全球分销至关重要。尽管已有大量关于骆驼奶的综述文献（例如 Farah, 1993; G. Konuspayeva & Faye, 2021; G. Konuspayeva, Faye, & Duteurtre, 2021; G. Konuspayeva, Faye, & Loiseau, 2009; G.S. Konuspayeva, 2020a,b; Kula & Tegegne, 2016; Shori, 2015; Yadav, Kumar, Priyadarshini, & Singh, 2015），但大多数集中于描述骆驼奶的组成、营养特性及某些骆驼奶产品的一般生产情况。目前仍缺乏针对所有可能骆驼奶产品生产技术方面的全面综述。因此，本综述重点探讨以骆驼奶为原料生产各类食品（包括巴氏奶/灭菌奶、发泡剂、奶粉、冰淇淋、奶酪、黄油和酸奶）的潜力。在更新现有骆驼奶产品生产现状的同时，我们也指出了加工过程中存在的挑战与局限性（如适用）。然而，理解骆驼奶产品生产的难点需要对其基本性质有深入了解。因此，本综述还介绍了骆驼奶的组成、营养价值、功能特性及其在热处理过程中的稳定性。

**2. 骆驼奶中的宏量营养素与生物活性化合物** 骆驼奶的组成已在全球范围内被广泛研究，大量文献数据显示其成分存在显著差异。2009年发表了一项关于骆驼奶组成文献数据的荟萃分析（Konuspayeva et al., 2009），并于2020年进行了更新（Konuspayeva 2020b）。表1汇总了来自不同地理来源的单峰骆驼奶的组成，并与牛乳和人乳进行了比较。

**2.1. 蛋白质** 骆驼奶中酪蛋白占总蛋白的61.8–88.5%（Ereifej et al., 2011）。骆驼酪蛋白组分包括αS1-酪蛋白、αS2-酪蛋白、β-酪蛋白和κ-酪蛋白，分别占总酪蛋白的21%、10%、65%和3.5%（Kappeler et al., 2003; Mati et al., 2017）。与人乳相似，骆驼奶含有高比例的β-酪蛋白（占总酪蛋白的65%）（Kappeler et al., 2003）。由于β-酪蛋白比αS-酪蛋白更易于肽键水解，其在骆驼奶中的高丰度被认为是骆驼奶易于被人类婴儿消化的主要原因之一（El-Agamy et al., 2009）。骆驼与牛乳酪蛋白的氨基酸组成非常相似，但骆驼酪蛋白含较少半胱氨酸而较多脯氨酸（Kappeler, 1998）。

骆驼奶乳清蛋白主要包括α-乳白蛋白、血清白蛋白、免疫球蛋白、乳凝集素（又称糖基化依赖性细胞黏附分子-1或GlyCAM-1）和乳铁蛋白。通过毛细管电泳测定，骆驼奶中α-乳白蛋白、血清白蛋白和乳铁蛋白的浓度分别为2.01、0.40和1.74 mg/mL（Omar et al., 2016）。骆驼奶中α-乳白蛋白和乳铁蛋白含量高，且缺乏β-乳球蛋白，这些特征与人乳高度相似（Hinz et al., 2012）。由于β-乳球蛋白是牛乳中的主要过敏原之一，其在骆驼奶中的缺失使其成为婴儿配方奶粉中极具前景的替代蛋白源。研究表明，骆驼奶因其蛋白质的低致敏性，可被视为人乳的替代品（El-Agamy, 2007）。

已在骆驼奶中鉴定出多种具有潜在抗菌活性的生物活性蛋白，包括乳铁蛋白、GlyCAM-1、免疫球蛋白、乳过氧化物酶、肽聚糖识别蛋白（PGRP）、溶菌酶和乳清酸性蛋白（Mati et al., 2017）。这些蛋白的理化性质和生物活性总结于表2。Mati等（2017）对骆驼奶蛋白及其在发酵/消化过程中释放的肽段的潜在生物活性进行了全面综述。

**2.2. 脂质** 根据骆驼奶组成的荟萃分析结果（表1），骆驼奶脂肪含量与其地理来源密切相关。Dreiucker和Vetter（2011）详细描述了骆驼奶脂肪酸组成，并与牛乳和人乳进行了比较。骆驼奶脂肪仅含少量短链脂肪酸（C4–C12），但长链饱和脂肪酸浓度高于牛乳和人乳脂肪。骆驼奶脂肪中支链脂肪酸含量最高（3.03%），而牛乳和人乳脂肪中分别为1.82%和0.36%（Dreiucker & Vetter, 2011）。

关于顺式单不饱和脂肪酸，骆驼奶脂肪除油酸（18:1 cis-9，17.2%）外，还含有较高浓度的棕榈油酸（16:1 cis-9，10.1%）（Dreiucker & Vetter, 2011）。

骆驼奶脂肪的熔点和凝固温度分别为41.9°C和30.5°C，而牛乳脂肪分别为32.6°C和22.8°C。骆驼奶脂肪熔点升高可能归因于其长链脂肪酸含量高、短链脂肪酸含量低以及反式18:1异构体的存在（Abu-Lehia, 1989）。乳脂熔融谱主要由高分子量三酰甘油（TAGs，≥C40）主导。骆驼奶脂肪中TAG C24–C40含量极低（<1%），而TAG C48–C52含量非常高，这被认为是其相比牛、山羊、绵羊、马、驴和水牛乳脂肪具有较高熔点的主要原因（Smiddy et al., 2012）。

乳脂球平均直径按升序排列为：骆驼奶（2.99 μm）、山羊奶（3.2 μm）、绵羊奶（3.78 μm）、牛乳（3.95 μm）和水牛乳（8.7 μm）。在骆驼、牛、绵羊、山羊和水牛乳中，较小脂肪球（0.1–4.0 μm）分别占总脂肪分布的80.6%、68.4%、55.3%、73.3%和23%（El-Zeini, 2006）。由于小脂肪球更易受脂酶作用，骆驼奶和山羊奶被认为更易被人体消化（Tomotake et al., 2006）。

**2.3. 乳糖** 单峰骆驼奶的乳糖含量与牛乳相似（表1）。研究发现，骆驼产犊时乳糖含量较低（2.8%，w/v），并在泌乳第一天上升至3.8%。自由饮水骆驼的平均乳糖含量升至5%，而脱水骆驼则降至2.9%。骆驼奶中乳糖浓度的变化被认为是其口感差异（有时甜、有时苦）的主要原因之一（Yagil & Etzion, 1980）。有趣的是，骆驼奶似乎是乳糖不耐受患者更安全、更健康的选择。骆驼奶易于消化的可能原因之一是其酪啡肽（casomorphin）浓度较低，可减少肠道蠕动，从而使乳糖在更长时间内暴露于乳糖酶作用之下（Cardoso et al., 2010）。另一个可能原因是生骆驼奶中L-乳酸含量是牛乳的100倍（Konuspayeva et al., 2019）。

**2.4. 矿物质与维生素** 单峰骆驼奶的平均灰分含量与牛乳相近，但远高于人乳（表1）。骆驼奶主要矿物质的平均值（mg/100 g）为：钙111.4；镁6.7；磷81.2；钠57.8；钾156.3；而牛乳中相应含量分别为119.9、13.4、95.0、49.7和147.0。人乳中这些矿物质浓度则低得多：分别为32.4、3.4、14.0、16.0和51.8 mg/100 g（Soliman, 2005）。骆驼奶、牛乳和人乳的钙磷比分别为1.5、1.29和2.1。由于婴儿配方奶粉中高磷酸盐可能导致高磷血症和低血清钙，基于骆驼奶的配方被认为更适合喂养婴儿（Kappeler, 1998）。此外，骆驼奶中铁浓度是牛乳的六倍（Sawaya et al., 1984；表1；Ziane et al., 2016）。

骆驼奶含有多种维生素，包括维生素A、C、D、E和B族维生素。骆驼奶以其高维生素C含量著称，是牛乳的3至5倍（Farah et al., 1992）。维生素B3浓度也高于牛乳，而牛乳中维生素A和B2含量更高（Farah et al., 1992; Haddadin et al., 2008; Sawaya et al., 1984; Stahl et al., 2006）。骆驼奶与牛乳中维生素B1和B6含量相近（Haddadin et al., 2008; Sawaya et al., 1984）。最近发表了一篇关于骆驼奶中不同类型维生素的全面综述（Faye et al., 2019）。

**3. 骆驼奶的生物学功能**

**3.1. 降血糖作用** 在骆驼资源丰富地区，饮用骆驼奶治疗糖尿病有着悠久传统（Mohamad et al., 2009）。印度拉贾斯坦邦一项研究发现，饮用骆驼奶的社区糖尿病患病率显著低于未饮用社区（0% vs. 5.5%）（Agrawal et al., 2007）。数十项临床研究已证实骆驼奶的抗糖尿病效果。Agrawal等（2003）报告，I型糖尿病患者饮用骆驼奶三个月后胰岛素需求量减少30%。此外，骆驼奶作为I型糖尿病辅助治疗手段的长期疗效和安全性已在1年和2年试验中得到证实（Agrawal et al., 2011; Agrawal et al., 2007）。骆驼奶也可能有助于控制II型糖尿病患者的胰岛素水平，因为饮用两个月后观察到胰岛素水平显著升高（Ejtahed et al., 2015）。动物模型研究也证实了骆驼奶的降血糖作用。糖尿病兔和狗分别接受骆驼奶4–5周后，血糖水平分别下降78%和47%（Sboui et al., 2010; Tantawy et al., 2010）。

骆驼奶的抗糖尿病特性先前被认为主要归因于其高含量的胰岛素及类胰岛素蛋白（Korish et al., 2015; Malik et al., 2012）。然而，Abou-Soliman等（2020）近期研究发现，骆驼奶经体外消化30分钟后未检测到胰岛素活性，酶联免疫吸附试验（ELISA）结果也为阴性。仍需更多体内研究以确认口服骆驼奶中胰岛素及类胰岛素蛋白的吸收情况。骆驼奶中其他成分也可能贡献其抗糖尿病活性，例如其中的抗氧化剂可能有助于调节人体高血糖状态（Limon et al., 2014）。

**3.2. 抗菌作用** 骆驼奶对革兰氏阳性菌和革兰氏阴性菌（如大肠杆菌、单核细胞增生李斯特菌、金黄色葡萄球菌、鼠伤寒沙门氏菌、肺炎克雷伯菌和产气荚膜梭菌）均表现出抗菌活性（Benkerroum et al., 2004; El Agamy & Ruppanneb, 1992; Othman, 2016）。骆驼奶的抗菌活性有助于治疗由细菌感染引起的疾病，如结核病（TB）和克罗恩病（Mal et al., 2000; Shabo et al., 2008）。除杀灭病原菌（分别为结核分枝杆菌和副结核分枝杆菌）外，骆驼奶中的生物活性蛋白（如免疫球蛋白）被认为有助于增强免疫力，从而促进愈合过程（Mal et al., 2006）。因此，症状缓解通常被视为骆驼奶杀菌与免疫调节作用共同作用的结果。

骆驼奶的抗菌活性主要源于其生物活性化合物，尤其是乳铁蛋白、溶菌酶和免疫球蛋白，这些成分在骆驼奶中含量丰富（Benkerroum et al., 2004; El Agamy & Ruppanneb, 1992）。此外，骆驼乳清蛋白经酶解后抗菌活性增强，提示体内消化后可能释放出抗菌活性更强的肽段（Salami et al., 2010）。骆驼奶乳铁蛋白还对丙型肝炎病毒基因型4表现出抗病毒活性，可完全抑制病毒进入白细胞（Redwan & Tabll, 2007）。骆驼奶还被认为具有抗真菌和抗寄生虫活性（Maghraby et al., 2005）。

**3.3. 免疫调节作用** 骆驼拥有独特而强大的免疫系统。据报道，骆驼抗体的大小远小于人类抗体。此外，骆驼奶中的IgG2和IgG3因天然缺乏轻链而具有独特性（Riechmann & Muyldermans, 1999）。骆驼免疫球蛋白（Igs）的小尺寸被认为有利于靶向特定抗原。骆驼IgG对破伤风毒素表现出完全中和活性，并被认为是更好的酶抗原抑制剂（Muyldermans et al., 2001; Riechmann & Muyldermans, 1999）。

骆驼奶疗法对自闭症儿童行为表现出令人惊讶的积极影响。尽管自闭症病因尚不明确，但研究认为其与氧化应激增加有关。饮用骆驼奶两周后，自闭症儿童血浆中谷胱甘肽、髓过氧化物酶和超氧化物歧化酶浓度显著升高，有助于控制氧化应激（Shabo & Yagil, 2005）。骆驼奶中免疫球蛋白的免疫修复作用也被认为是减轻自闭症儿童潜在乳制品过敏的可能因素（Al-Ayadhi et al., 2015）。

**3.4. 低致敏性** 牛乳过敏是儿童和成人中最常见的食物过敏之一，临床症状多样且可能非常严重。牛乳中含有超过20种可引发过敏反应的蛋白质，其中酪蛋白组分（尤其是αS1-酪蛋白）和β-乳球蛋白是两种最强的过敏原（El-Agamy, 2007）。人乳成分分析显示其不含β-乳球蛋白，αS1-酪蛋白浓度低而β-乳蛋白浓度高（El-Agamy et al., 2009）。骆驼奶的蛋白质组成与人乳相似，表明其作为过敏儿童牛乳替代品具有巨大潜力（El-Agamy, 2007）。临床试验也取得了令人鼓舞的结果，骆驼奶用于治疗牛奶过敏儿童（Shabo et al., 2005）。骆驼奶甚至被认为是乳糖不耐受人群的更好选择，因为其乳糖可被快速消化（Cardoso et al., 2010）。不过，仍需更大规模试验以支持这一论断。

**3.5. 血管紧张素I转换酶（ACE）抑制活性** 血管紧张素I转换酶（ACE）是一种二肽基羧肽酶，可调节血压，抑制ACE可导致血压下降。多种食物蛋白（包括乳蛋白）中已发现具有ACE抑制活性的肽段（Minervini et al., 2003）。在骆驼奶水解物和发酵骆驼奶中也发现了ACE抑制肽（Soleymanzadeh et al., 2019; Tagliazucchi et al., 2016）。Quan等（2008）从发酵骆驼奶中纯化出一种ACE抑制肽（AIPPKKNQD），该肽在蛋白酶消化或热处理后仍保持ACE抑制活性，表明其在体内消化后具有抗高血压潜力。

**4. 热处理对骆驼奶营养价值的影响**

**4.1. 骆驼奶的热稳定性** 乳的热稳定性是考虑其热处理时的重要参数。Farah和Atkins（1992）研究了pH 6.3–7.1条件下骆驼奶在100、120和130°C下的热凝固时间（HCT）。在120和130°C时，乳在所有pH值下均极不稳定，HCT低于2–3分钟。在100°C时，HCT最初升至12分钟，在pH 6.4–6.7间保持稳定，随后随pH升高而逐渐增加，在pH 7.1时达到约33分钟。骆驼奶的热稳定性似乎远低于牛乳（Farah, 1993）。另一项研究发现，在140°C下，牛乳、水牛乳和骆驼奶的HCT分别为1807.4、1574.6和133.6秒（Shyam et al., 2016）。

κ-酪蛋白和β-乳球蛋白的存在及其加热过程中的相互作用被认为对维持乳的稳定性至关重要（Farah & Atkins, 1992）。因此，骆驼奶中κ-酪蛋白含量较低（占总酪蛋白的5%，而牛乳为13.6%）以及缺乏β-乳球蛋白，可能是其在高温下稳定性差的原因。

**4.2. 骆驼奶蛋白的热稳定性** 为开发适合骆驼奶的热加工技术，有必要研究其蛋白质的热稳定性，以评估其在热处理过程中能否保持功能特性。不同研究采用了不同的热处理条件。当乳在63、80和90°C加热30分钟（Farah, 1986）或在65、75、85和100°C加热10、20和30分钟（Elagamy, 2000）时，骆驼奶乳清蛋白比牛乳和水牛乳蛋白更具热稳定性。通过测定分离乳清组分在pH 4.0、4.5、5.0和7.0下于60–100°C加热1小时后的溶解度变化，间接评估了骆驼与牛乳乳清蛋白的热稳定性——变性蛋白会沉淀，导致乳清蛋白溶解度下降（Laleye et al., 2008）。温度对溶解度的影响取决于pH，在pH 4.5（许多乳清蛋白的等电点）时溶解度发生显著变化。在pH 7时，牛乳和骆驼乳清蛋白均最稳定，此时展开的球蛋白之间的静电排斥抑制了聚集过程。在pH 4.5和100°C下，骆驼和牛乳乳清蛋白的溶解度分别下降了55%和52%。骆驼乳清蛋白对酸变性更敏感：当pH从7降至4时，骆驼乳清蛋白溶解度下降约16%，而牛乳仅下降9%。Felfoul等（2015）发现，骆驼血清白蛋白、α-乳白蛋白和κ-酪蛋白条带在90°C加热后减弱。牛乳血清白蛋白在70°C加热后即从电泳图谱中消失，而β-乳球蛋白和α-乳白蛋白条带仅在90°C时才消失。此外，游离硫基浓度分析表明，70°C下骆驼蛋白未发生显著变性，而牛乳在70°C加热30分钟后完全变性。Genene等（2019）近期也通过乳清蛋白氮分析发现，骆驼奶乳清蛋白的热变性程度低于牛乳。SDS-PAGE结果显示，骆驼奶在90°C加热5分钟后，α-乳白蛋白变性率为33%，而牛乳高达95%。

差示扫描量热法（DSC）有时用于测定骆驼奶蛋白的变性温度。浓缩骆驼奶和牛乳的变性峰分别出现在77.8°C和81.7°C（Felfoul et al., 2015）。当使用DSC分析液态和干燥状态的骆驼与牛乳乳清样品时，干燥骆驼乳清在139、180和207°C出现三个微弱热转变，而干燥牛乳乳清的三个峰分别出现在81、146和198°C。然而，液态骆驼与牛乳乳清蛋白的热变性曲线无显著差异（Laleye et al., 2008）。由于这些峰代表蛋白混合物，其数值可能不足以得出乳清蛋白稳定性的可靠结论。

总体而言，骆驼奶乳清蛋白似乎比牛乳乳清蛋白更具热稳定性，尽管乳源、测试条件和检测方法的不同可能导致上述结果存在不一致。这些研究通常将乳清蛋白作为整体进行分析，有时使用蛋白凝胶追踪主要乳清蛋白的变化。未来需对乳清蛋白（尤其是具有抗菌活性的蛋白，其中一些在乳中含量较低）在热处理过程中的行为进行更详细研究，以为骆驼奶加热加工提供全面信息。

骆驼奶中某些单一生物活性蛋白的热稳定性也已得到研究。通常需先进行蛋白纯化再进行稳定性分析。骆驼乳清蛋白的热稳定性排序为：溶菌酶 > 乳铁蛋白 > IgG（Elagamy, 2000）。骆驼α-乳白蛋白在热变性过程中的二级结构保存优于牛乳α-乳白蛋白（Atri et al., 2010）。骆驼奶乳过氧化物酶在67–73°C加热时热稳定性低于牛乳（Tayefi-Nasrabadi et al., 2011）。

蛋白质组学方法也被应用于热处理对骆驼奶蛋白影响的研究。与传统方法相比，这些方法可同时高效定量大量蛋白，为分析单一骆驼奶蛋白的热变性提供了更灵敏、准确的替代方案。Zhang等（2016）研究并比较了冷冻、巴氏杀菌和喷雾干燥对骆驼、牛和山羊奶蛋白的影响。在牛、骆驼和山羊奶血清中分别定量了129、125和74种蛋白。不同加工步骤和物种间蛋白浓度变化速率不同。一些免疫相关蛋白（如乳铁蛋白、GlyCAM-1和乳凝集素）对热敏感，巴氏杀菌后损失约25–85%，喷雾干燥后损失85–95%。而α-乳白蛋白、骨桥蛋白和乳清酸性蛋白相对热稳定，巴氏杀菌后损失10–50%，喷雾干燥后损失25–85%。另一方面，冷冻后来自受损乳脂球和体细胞的某些蛋白浓度增加。

Felfoul等（2017）采用液相色谱-串联质谱（LC-MS/MS）鉴定了80°C加热60分钟前后牛乳和骆驼奶蛋白。α-乳白蛋白、PGRP和血清白蛋白被鉴定为骆驼奶主要乳清蛋白，其热敏感性顺序为：α-乳白蛋白 < PGRP < 血清白蛋白（加热后分别下降100%、68%和42%）。牛乳中两种主要乳清蛋白α-乳白蛋白和β-乳球蛋白在热处理后分别剩余0%和26%。此外，通过SDS-PAGE分离出19个蛋白条带，并用LC-MS/MS鉴定。结果证实骆驼α-乳白蛋白和PGRP以及牛乳α-乳白蛋白和β-乳球蛋白对80°C热处理敏感。同时，骆驼与牛乳中的酪蛋白组分在80°C加热60分钟后仍保持完整。

Benabdelkamel等（2017）采用定量二维差异凝胶电泳-质谱法全面研究了骆驼奶乳清蛋白在63°C和98°C加热1小时后的变性情况。与未加热乳样相比，63°C加热乳样中共有80种蛋白显著减少，而在63°C加热乳中保持稳定的25种蛋白在98°C加热乳中显著减少。酶类受加热影响最严重，其次是结合蛋白和细胞黏附蛋白。免疫相关蛋白占所有受热影响蛋白的5%。

近期发表了两项研究，探究喷雾干燥骆驼奶粉的蛋白谱变化。Zouari等（2020）对脱脂骆驼奶和牛乳进行喷雾干燥，并使用HPLC-MS对干燥前后蛋白进行鉴定和定量。骆驼奶粉中蛋白变性程度低于牛乳粉。喷雾干燥后，骆驼血清白蛋白和α-乳白蛋白浓度分别下降14.1%和3.3%，而骆驼PGRP和酪蛋白浓度保持不变或有所增加。Li等（2020）比较了未加工骆驼奶、加热液态骆驼奶（115°C，15分钟）和骆驼奶粉的蛋白谱。蛋白经串联质量标记标记后进行LC-MS/MS分析。在鉴定的807种蛋白中，与未加工乳相比，加热液态乳和奶粉中分别有246种和170种蛋白发生显著变化。加工后下降最显著的蛋白包括ARF GTP酶激活蛋白GIT1、延伸因子1-α1、酰基辅酶A去饱和酶、热休克蛋白90和醛氧化酶3样蛋白。由于本研究使用双峰骆驼奶，其蛋白组成可能与其他研究中使用的单峰骆驼奶有所不同。

不同的加工条件和分析方法可能导致上述部分结果不一致。例如，Felfoul等（2017）研究发现骆驼奶中α-乳白蛋白热稳定性低于血清白蛋白，而Zouari等（2020）研究则相反。关于热处理对骆驼奶蛋白质组影响的研究仍处于早期阶段，仍需更多研究以阐明各种加工过程（尤其是对生物活性蛋白）的影响。

**5. 以骆驼奶为原料的潜在食品**

**5.1. 巴氏奶与灭菌骆驼奶** 从物理性质看，骆驼奶呈白色，略带咸味并伴有微甜余味，与牛乳相似。相比牛乳，骆驼奶含有更高水平的矿物质（如铁）、维生素C、抗菌和益生菌化合物，更高的乳清蛋白与酪蛋白比例，且缺乏致敏蛋白（β-乳球蛋白）。这些因素使骆驼奶比牛乳更易消化，且在营养价值上最接近人乳（El-Agamy, 2006）。由于抗菌成分浓度较高，生（新鲜）骆驼奶的保质期比牛乳更长（Faraz et al., 2013）。通过产过氧化氢的乳酸菌（如W. confusa 22282）激活骆驼奶中的天然抗菌系统（如乳过氧化物酶系统），被报道为维持生骆驼奶储存稳定性的替代方法（Dashe et al., 2020）。从营养角度看，像加工牛乳一样加工骆驼奶供人类消费是可行的。然而，尽管骆驼奶在许多国家市场上已有销售，但其在日常人类饮食中的使用仍然有限。Konuspayeva等（2021）在其研究中列出了从阿里巴巴销售平台获取的骆驼奶供应商名单。大多数骆驼奶产品为巴氏奶，约在72°C加热15秒以杀灭有害病原体，使产品在冷藏条件下可保存两周（Ipsen, 2017）。研究表明，在与牛乳相同的条件下对骆驼奶进行巴氏杀菌不会对其功能特性造成显著改变。在低于100°C的温度下，骆驼奶中的乳清蛋白和抗菌因子比牛乳更稳定（Elagamy, 2000; Farah, 1986），且骆驼奶与牛乳中病原菌（如大肠杆菌）的热灭活效果相似（Sela et al., 2003）。

商业巴氏骆驼奶未经均质化处理。储存期间，由于脂肪上浮，表面会形成一层薄薄的白奶油层。在相同条件下，骆驼奶的上浮速率远低于牛乳。4°C下储存24小时后，骆驼奶的上浮程度仅为牛乳的十二分之一（Farah & Rüegg, 1991）。因此，鉴于巴氏骆驼奶保质期较短，均质化处理可能并非必要。骆驼奶上浮缓慢归因于其脂肪球较小。如图1（未发表数据）所示，生牛乳和骆驼奶的粒径分布显示，基于体积平均粒径（D[4,3]），骆驼奶的平均粒径为2.56 μm，而牛乳几乎为其两倍（4.16 μm）。此外，骆驼奶中缺乏促进脂肪球聚集的凝集素蛋白，也导致其上浮能力较低（Farah & Rüegg, 1991）。尽管饮用骆驼奶有许多健康益处，但由于产量低、生产成本高，其极高的零售价（例如美国约38美元/升，新加坡约19美元/升，澳大利亚约15美元/升，印度约7美元/升）可能是限制其用于人类日常消费的主要原因。

骆驼奶在高温下热稳定性极差，在自然pH下无法灭菌，因蛋白质会变性并沉淀。因此，生产灭菌骆驼奶非常困难。如第4.1节所述，当加热温度从100°C升至140°C时，骆驼奶的凝固时间从12分钟缩短至不足1分钟（Farah & Atkins, 1992）。骆驼奶在高温下的低稳定性与κ-酪蛋白缺乏及β-乳球蛋白缺失有关。然而，骆驼奶在高温下的热稳定性随pH升高和磷酸盐的存在而提高。将pH提高至6.9–7.2或向骆驼奶中添加磷酸钠（1 mmol/L）后，在121°C加热15分钟不会引起蛋白质沉淀或仅产生极少量可逆沉淀（Alhaj et al., 2011）。与巴氏杀菌（72.5°C/15秒）和高压处理（200–800 MPa）相比，超高温灭菌（UHT，144°C/5秒）导致骆驼奶颜色变化最大、乳清蛋白变性程度最高（Omar et al., 2018）。UHT骆驼奶中α-乳白蛋白变性率约为66%，几乎是高压处理骆驼奶（约33%）和巴氏骆驼奶（约27%）的两倍。就颜色而言，UHT乳的总色差（ΔE）值为6.5，而巴氏乳和高压处理乳的ΔE分别为1.5和2.26。此外，压力高于400 MPa的处理和UHT均抑制了骆驼奶的凝乳酶凝固。该研究进一步凸显了骆驼奶灭菌面临的挑战，并表明高压处理（<400 MPa）因其对骆驼奶特性的负面影响小于UHT，可作为骆驼奶保藏的潜在替代方法。

未来骆驼奶UHT研究方向包括研究多种添加剂（如磷酸二钠、牛源κ-酪蛋白和钙螯合剂（如乙二胺四乙酸二钠盐））以稳定骆驼奶蛋白，以及使用亲水胶体提高粘度并减少UHT骆驼奶的沉淀（Alhaj et al., 2011）。pH的微小变化似乎对骆驼奶热稳定性产生显著影响，因为κ-酪蛋白和钙含量是影响骆驼奶热稳定性的主要因素（Alhaj et al., 2011）。目前，Camelicious（阿联酋骆驼奶与产品工业公司）正在全球销售一款UHT骆驼奶产品，在阴凉干燥处储存保质期可达12个月（Yirda et al., 2020）。然而，该产品由复原全脂骆驼奶粉制成。

**5.2. 发泡剂** 许多乳制品（如卡布奇诺式饮品）表面的顶层泡沫决定了整体产品质量和消费者接受度。大多数咖啡店使用牛乳制备泡沫，但牛乳中的致敏蛋白可能不适合乳制品过敏人群。骆驼奶因缺乏过敏原β-乳球蛋白而成为制备泡沫的潜在替代选择。在不同温度和pH条件下，骆驼奶及其蛋白的发泡性能与牛乳相当（Laleye et al., 2008）。

在pH 7.0下，骆驼甜乳清蛋白（通过离心从凝乳酶凝胶中分离）的发泡能力和泡沫稳定性仅略逊于牛乳甜乳清蛋白（Laleye et al., 2008）。然而，在70°C和90°C热处理后，骆驼酸乳清蛋白（将新鲜骆驼奶酸化至pH 4.3后离心获得）的发泡能力和泡沫稳定性显著高于其牛乳对应物（Lajnaf et al., 2018）。在pH < 5.0时，骆驼α-乳白蛋白失去结合的Ca²⁺，呈现具有高表面活性的熔融球态，有利于界面吸附和分子间相互作用，从而形成黏弹性薄膜（Lam & Nickerson, 2015）。骆驼α-乳白蛋白占酸乳清蛋白的绝大部分（>70%），因此酸乳清蛋白表现出良好的发泡行为。纯态下，β-酪蛋白的发泡性能优于α-乳白蛋白（Lajnaf et al., 2017）。骆驼奶的热处理（70–100°C/30分钟）也改善了发泡性能，因为骆驼奶蛋白的热变性和聚集导致表面疏水性增加、界面张力降低以及负电荷减少。此外，加热诱导的二级结构变化及其高疏水性也是骆驼奶蛋白发泡性能提升的原因（Lajnaf et al., 2020）。这些发现对乳制品加工商有益，有助于评估骆驼奶泡沫在卡布奇诺式饮品中商业化应用的潜力。

**5.3. 奶粉** 在不损害其生物活性成分的前提下生产干燥骆驼奶粉，已成为实现骆驼奶全球供应、延长保质期、降低运输成本及拓展其应用的重要途径。市场上已有多种骆驼奶粉产品，其中一些为非品牌产品。大多数采用冷冻干燥技术生产，因为冷冻干燥的低干燥温度有助于保护骆驼奶中的生物活性化合物，特别是其蛋白质的功能特性。据报道，冷冻干燥骆驼奶不会引起营养特性（如矿物质、维生素、氨基酸组成、生物价、蛋白质效率比、净蛋白质利用率和脂肪酸谱）相比新鲜骆驼奶发生显著变化（Ibrahim & Khalifa, 2015）。在相同冷冻干燥条件下生产的骆驼奶与牛乳粉的其他理化性质（如颜色、流动性和密度）无显著差异，且与商业牛乳粉相似，但骆驼奶粉的不溶性是牛乳粉的两倍（Sulieman et al., 2018）。然而，冷冻干燥众所周知是一种耗时且昂贵的脱水技术，不适合大规模生产干燥乳粉（Ortega-Rivas et al., 2005）。此外，冷冻干燥后，骆驼奶粉需研磨和筛分以获得理想的粒径均匀性。骆驼奶本身价格高昂，加上冷冻干燥操作成本高，导致骆驼奶粉成本极高。

喷雾干燥被认为是生产乳粉最合适的单元操作。然而，与牛乳粉相比，采用喷雾干燥技术生产骆驼奶粉仍处于研发早期阶段。低温（<60°C）喷雾干燥可能适用于骆驼奶粉生产，市场上也有少量喷雾干燥骆驼奶粉产品。由于缺乏不同来源骆驼奶营养成分和化学组成差异的信息，无法对喷雾干燥与冷冻干燥骆驼奶粉的营养价值进行比较。已有若干关于骆驼奶喷雾干燥的研究报告（Habtegebriel et al., 2018a, 2018b; Ho et al., 2019; Ho et al., 2021; Ogolla et al., 2019; Sulieman et al., 2014; Zouari et al., 2018; Ho et al., 2020）。这些研究致力于探究喷雾干燥操作条件（进风温度、出风温度、干燥空气流速、进料流速、进料方向和雾化压力）及进料物料特性（固形物浓度和脂肪含量）对所得骆驼奶粉物理、光学和热学特性（产量、堆积密度、颜色、溶解度、颗粒形态、玻璃化转变温度、水分活度、维生素C回收率、脂肪酸谱）的影响。一般而言，采用并流方向的喷雾干燥在水分活度、亮度、溶解度、流动性和粉末产量方面可获得更优质的骆驼奶粉（Sulieman et al., 2014）。此外，喷雾干燥骆驼奶粉的产量还取决于进风干燥温度、进料流速和进料固形物含量。产量随进风干燥温度和进料流速的增加而提高，但随进料固形物含量的增加而下降（Habtegebriel et al., 2018a, 2018b）。

在较高温度、较高进料流速和高脂肪含量条件下进行喷雾干燥会降低奶粉的复水性能（润湿性、分散性和溶解度）（Habtegebriel et al., 2018a; Ogolla et al., 2019）。在进风和出风干燥温度分别为160°C和70°C条件下生产的鲜骆驼奶粉具有极高的溶解度（98.62 ± 1.47%），在37°C和低相对湿度（<33%）下加速储存18周后仅略有下降（Ho et al., 2019）。储存期间，表面脂质含量增加导致表面疏水性增强以及粉末颗粒轻微聚集，是骆驼奶粉溶解度随储存时间和相对湿度增加而下降的主要原因（Ho et al., 2021）。喷雾干燥骆驼奶粉的高溶解度使其在食品加工中具有广泛应用前景，因为复水是乳粉掺入食品产品的前提。喷雾干燥骆驼奶粉已被研究作为生产加工奶酪酱中替代奶酪基料的新型功能原料。添加10%喷雾干燥骆驼奶粉可显著改善奶酪酱的品质属性，尤其是感官特性（Desouky et al., 2019）。

在颗粒形态方面，喷雾干燥骆驼奶粉表面光滑，覆盖有脂肪层，无晶体结构（Habtegebriel et al., 2018a; Ho et al., 2019; Ogolla et al., 2019）。Zouari等（2020a）发现，喷雾干燥骆驼奶粉的表面粗糙度远低于其牛乳对应物，且在液滴形成过程中，大多数骆驼奶脂肪球被蛋白包裹在粉末表面附近。然而，Ho等（2021）的研究中，X射线光电子能谱分析结果表明，新鲜喷雾干燥骆驼奶粉表面以脂质为主（约78%），其次是蛋白质（约16%）和乳糖（约6%）。储存期间表面脂质含量增加（例如在33% RH下储存18周）导致具有褶皱和折叠表面、带有凹痕和含有干燥乳粉小颗粒的大液滴的粉末颗粒聚集（图2a和2b）。此外，新鲜喷雾干燥骆驼奶粉的X射线衍射分析显示粉末具有一定程度的结晶性，在其X射线衍射图谱中观察到一些小而尖锐的峰（图2c）（Ho et al., 2019）。对喷雾干燥骆驼奶粉生化特性的分析表明，α-和β-酪蛋白在喷雾干燥过程中非常稳定，而约14%的血清白蛋白发生变性（Zouari et al., 2020b）。同时，喷雾干燥骆驼奶粉的乳清蛋白氮指数（约11.5%）与其牛乳粉对应物（约9.0%）相近。这些研究增强了通过喷雾干燥生产骆驼奶粉的可能性。然而，仍需进一步研究，特别是关于喷雾干燥后骆驼奶生物功能保留情况的研究。

在实验室和工厂规模应用中，喷雾干燥用于骆驼奶粉生产可能存在许多局限性。首先，骆驼奶生产仅限于某些地理区域，如部分亚洲和非洲国家以及澳大利亚。重要的是，预浓缩（以提高骆驼奶固形物浓度）和喷雾干燥阶段的高温操作可能会使骆驼奶中的营养和功能蛋白变性（Lajnaf et al., 2018）。由于固形物浓度低（约10%，w/w），直接对骆驼奶进行喷雾干燥不经济。在乳粉生产中，将乳浓缩至固形物浓度达40–50%（w/w）是不可或缺的环节，不仅可降低干燥过程能耗，还有助于赋予干燥粉末理想特性（Roy et al., 2017）。浓缩和喷雾干燥技术的最新进展可能允许在低温下对骆驼奶粉进行预浓缩和喷雾干燥。

**5.4. 冰淇淋** 冰淇淋是一种甜味冷冻产品，是全球最受欢迎的乳制品甜点之一，通常由牛乳添加各种配料制成。由于骆驼奶优于牛乳的特性，食用骆驼奶制成的冰淇淋可能比牛乳产品更受青睐。骆驼奶冰淇淋结合了冰淇淋和骆驼奶的优点，可满足功能性食品的需求（如低脂冰淇淋）。目前市场上已有多种此类产品。基本上，骆驼奶冰淇淋的生产工艺与牛乳冰淇淋相似，包括配料混合、巴氏杀菌、均质化、冷却、老化（约4°C）、通过刮板式冷冻机（-5°C）（或类似设备）在剪切下冷冻以掺入空气形成泡沫结构、添加风味配料（如适用）、包装以及速冻至-25至-30°C（Goff & Hartel, 2013）。当采用相同配方时，骆驼奶冰淇淋的熔点、干物质含量和粘度均低于牛乳冰淇淋，这是由于骆驼奶与牛乳的干物质含量不同（分别为10.02%和12.30%）。然而，两者在脂肪和蛋白质含量、酸度以及感官特性（颜色、风味、质地和口感）方面相似（Jafarpour, 2017）。骆驼与牛乳冰淇淋在消费者接受度（质地、味道、风味和颜色）方面也无显著差异（Hassan, 2009）。近期研究表明，可使用多种添加剂和风味剂成功加工骆驼奶冰淇淋，以丰富其营养和健康益处，并为消费者提供愉悦风味（Ahmed & El Zubeir, 2015; Salem et al., 2017）。在骆驼奶冰淇淋中添加2%骆驼奶酪蛋白及其水解物可提高其粘度、稠度和抗融性，降低硬度和膨胀率，并改善感官特性（Hajian et al., 2020）。骆驼酪蛋白在低脂奶油和乳液配方中的优异表面活性也被报道（Ziaeifar et al., 2018）。

**5.5. 黄油** 尽管骆驼奶脂肪含量与牛乳相当（约2.30–3.95%），但从骆驼奶生产黄油非常困难，且牛乳黄油生产工艺无法直接用于骆驼奶，因其脂肪和蛋白质的物理化学性质存在差异。因此，有作者声称无法从骆驼奶制作黄油（Yagil et al., 1994）。骆驼奶几乎不发生脂肪上浮，原因在于其缺乏促进脂肪球聚集的凝集素蛋白，脂肪球尺寸小，且脂肪与蛋白质结合紧密。此外，骆驼奶脂肪的高熔点（由脂肪酸谱中长链脂肪酸比例高及较厚的脂肪球膜引起）使得骆驼奶奶油的搅打过程只能在高于牛乳常用温度（10–14°C）的条件下进行（Asresie et al., 2013; Berhe et al., 2017; Farah & Fischer, 2004; Fuquay et al., 2011）。

事实上，苏丹、肯尼亚、埃及、阿尔及利亚和巴基斯坦的游牧民在大约20–30年前已使用新鲜、酸化或发酵骆驼奶及骆驼奶奶油手工生产骆驼奶黄油。然而，这些手工工艺无法获得高黄油得率（El-Agamy, 2006）。实际上，过去二十年间已开发出具有改进黄油得率的骆驼奶黄油受控生产工艺（Farah et al., 1989），如图3所示。该工艺中，骆驼奶首先加热至65°C并离心分离奶油。将奶油标准化至20–30%脂肪含量后，可选择接种2%发酵剂以生产酸奶油或甜奶油。酸奶油和甜奶油均在15–36°C下搅打，黄油粒在27°C水中洗涤。结果表明，在相同脂肪含量和搅打温度下，酸奶油获得的黄油得率显著低于甜奶油。对于甜奶油，当奶油脂肪含量为20–25%、搅打温度为15–20°C时，可获得最高黄油得率（80–85.3%），对应搅打时间为10–18分钟。此外，在低温（<12°C）下搅打无法获得黄油粒，而当搅打温度高于36°C时，黄油得率显著下降。Berhe等（2013）报道了另一种提高发酵骆驼奶黄油得率的方法（图3）。将骆驼奶在室温下发酵至pH 4.10，然后在22–23°C下沿垂直方向剧烈搅打，而非传统方法的前后运动。该方法因搅打力大而获得高黄油得率（约80%），但搅打时间非常长（约120分钟）。尽管从科学角度看生产骆驼奶黄油是可能的，但要与牛乳黄油竞争，仍需大量研究以解决搅打工艺和黄油得率方面的局限性。

在黄油品质方面，骆驼奶黄油具有白色、粘性、油腻感、高熔点、短链脂肪酸含量低和风味强度弱的特点。骆驼奶黄油不仅可作为食用油脂用于烹饪，还因传统制作过程中使用的微生物群具有益生菌特性而用于药用目的（Ipsen, 2017; Maurad & Meriem, 2008; Mourad & Nour-Eddine, 2006）。

**5.6. 奶酪** 从骆驼奶生产奶酪比其他哺乳动物乳（牛、水牛、绵羊和山羊）更困难且复杂，原因在于凝固时间长、得率低和凝乳脆弱（Ramet, 2001）。奶酪硬度取决于κ-酪蛋白与总酪蛋白的比例，该比例越高，奶酪越硬。然而，骆驼奶中该比例约为3.5%，远低于牛乳（约13%）和水牛乳（13–20%）。此外，骆驼κ-酪蛋白的凝乳酶切割位点与牛源对应物完全不同。骆驼κ-酪蛋白的凝乳酶切割位点位于Phe97-Ile98氨基酸序列，而牛乳为Phe105-Met106。这些特性，加上骆驼奶因高抗菌化合物含量而抑制细菌生长，导致骆驼奶凝固延迟并形成软凝乳。骆驼奶酪胶束尺寸较大是其凝乳酶凝固性差的另一特征。骆驼酪蛋白胶束尺寸约为380 nm，几乎是牛乳酪蛋白胶束（150 nm）的两倍（Berhe et al., 2017; El-Agamy, 2006）。尽管存在这些局限性，已有大量研究致力于生产多种类型的骆驼奶奶酪，总结于表3。关于游牧民家庭规模生产骆驼奶奶酪的细节由El-Agamy（2006）综述。近期，Konuspayeva（2020a）详细描述了骆驼奶奶酪生产在技术开发、文化满足和商业化方面面临的挑战。

生产骆驼奶奶酪的一种简单方法是将骆驼奶与其他非牛乳（如水牛乳）混合以提高酪蛋白含量。在相同加工条件下，软质未成熟水牛奶酪的得率（水牛乳为12.22%，骆驼奶为5.49–7.68%）高于其骆驼奶对应物，且在感官和物理特性方面更优（Inayat et al., 2007）。因此，将30%（w/w）水牛乳与骆驼奶混合可改善凝乳酶凝固性和凝乳硬度，提高得率，减少腌制过程中的重量损失，并增强奶酪的微生物学品质和感官特性（Shahein et al., 2014）。出于类似原因，也有将绵羊奶与骆驼奶混合生产软质奶酪的报道（Saadi et al., 2019）。

软质奶酪是最受欢迎的骆驼奶奶酪。已有多种使用不同凝固剂生产骆驼奶软质奶酪的工艺。Mohamed等（2013）发现，通过直接酸化（60%乙酸，pH 4.3）凝固骆驼奶可简单制备具有可接受感官特性的新鲜软质奶酪。然而，Mbye等（2020）近期研究报道，使用乙酸（每升奶30%酸）作为凝固剂生产软质未成熟骆驼奶酪会导致产品产生刺鼻气味和酸味。此外，Mehaia（1993）声称不鼓励在不使用发酵剂的情况下制作骆驼奶奶酪，因为这会导致奶酪水分和pH高、得率低、感官特性差。Ahmed和Kanwal（2004）也指出，使用从骆驼奶中分离的发酵剂（S. cremoris和S. lactis）可生产更高质量的骆驼奶软质奶酪。Abu-Tarboush（1996）推荐使用混合菌种（S. thermophilus和L. delbrueckii ssp. bulgaricus）以获得生产骆驼奶奶酪和酸奶的理想特性。这些研究强调了发酵剂在骆驼奶奶酪制作中的重要性。不同发酵剂对产品的理化质地特性和消费者偏好有不同影响。非芳香