Ultrasound and Thermosonication as Promising Technologies for Processing Plant-Based Beverages: A Review

✅ 全文

超声和热超声作为植物基饮料加工的前沿技术:综述

作者 Dalia M. Sotelo-Lara; Genaro G. Amador‐Espejo; Diego F. Álvarez-Araiza; Alondra K. Cordero-Rivera; Karla G. Millán-Quintero; Rocío Campos-Vega; Rita M. Velázquez-Estrada 期刊 Food Technology and Biotechnology 发表日期 2024 ISSN 1330-9862 DOI 10.17113/ftb.62.04.24.8624 类型 原创研究 (Original Research)

📄 英文摘要 English Abstract

EN

Plant-based beverages are water-soluble extracts of cereals, pseudocereals, seeds and legumes that resemble milk in appearance. However, these products have important differences compared to normal liquid milk, such as nutritional composition, sensorial properties and shelf-life stability. Increasing number of consumers are opting for these beverages due to lactose intolerance, milk protein allergies or lifestyle. In this regard, different emerging technologies have been investigated to solve problems such as shelf life, nutritional and emulsion stability as well as sensory acceptability, without using high temperatures since heat treatments decrease the content of some bioactive compounds. Ultrasound technology alone or combined with temperature (thermosonication) could be a valuable tool to improve the properties of plant-based beverages. Therefore, this review provides a detailed analysis of the effect of ultrasound and thermosonication on the physical, bioactive, microbiological and sensory properties of almond-, soybean-, coconut-, hazelnut- and peanut-based beverages, among others.

📄 中文摘要 Chinese Abstract

中文
植物基饮料是谷物、假谷物、种子和豆类的可溶性提取物,外观与牛奶相似。然而,这些产品与普通液态奶在营养成分、感官特性和保质期稳定性等方面存在重要差异。由于乳糖不耐受、牛奶蛋白过敏或生活方式等原因,越来越多的消费者选择此类饮料。为此,人们研究了各种新兴技术,以在不使用高温的情况下解决保质期、营养和乳液稳定性以及感官可接受性问题,因为热处理会降低某些生物活性物质的含量。超声波技术单独使用或与温度结合(热超声处理)可能是改善植物基饮料特性的有效工具。

📋 英文结构化总结 English Structured Summary

全文整理

EN

Header:

Background

Plant-based beverages are water-soluble extracts of cereals, pseudocereals, seeds and legumes that resemble milk in appearance. However, these products have important differences compared to normal liquid milk, such as nutritional composition, sensorial properties and shelf-life stability. Increasing number of consumers are opting for these beverages due to lactose intolerance, milk protein allergies or lifestyle. In this regard, different emerging technologies have been investigated to solve problems such as shelf life, nutritional and emulsion stability as well as sensory acceptability, without using high temperatures since heat treatments decrease the content of some bioactive compounds. Ultrasound technology alone or combined with temperature (thermosonication) could be a valuable tool to improve the properties of plant-based beverages.

Header:

Methods

N/A - Review article.

Header:

Results

The review provides a detailed analysis of the effect of ultrasound and thermosonication on the physical, bioactive, microbiological and sensory properties of almond-, soybean-, coconut-, hazelnut- and peanut-based beverages, among others. Ultrasound, defined as pressure waves with frequencies above 20 kHz, induces the formation of microbubbles through cavitation within the food system. Combining ultrasound with moderate heat (50–60 °C), also known as thermosonication, has been effective in microbial inactivation and reducing enzymatic activity. Furthermore, ultrasound has shown potential to reduce particle size and enhance physical stability.

Header:

Data Summary

According to the data collected by Grand View Research (18), the consumption of plant-based beverages (cow’s milk substitutes) based on almonds, soybeans, oats and nuts has increased worldwide by 33.5 % in the last five years. This market was valued at USD 26.80 billion in 2022 and is expected to reach a compound annual growth rate of more than 13.1 % from 2023 to 2030 (18). North America is estimated to have the largest revenue in the global market of vegetable beverages, although Asia is expected to be the fastest growing region, including countries such as China, India and South Korea (20).

Header:

Conclusions

Ultrasound technology alone or combined with temperature (thermosonication) could be a valuable tool to improve the properties of plant-based beverages. Therefore, this review provides a detailed analysis of the effect of ultrasound and thermosonication on the physical, bioactive, microbiological and sensory properties of almond-, soybean-, coconut-, hazelnut- and peanut-based beverages, among others.

Header:

Practical Significance

Various non-thermal technologies such as high hydrostatic pressure, pulsed electric field, microwave, irradiation and ultrasound have been developed to address the degradation of bioactive compounds caused by traditional heat treatments. These technologies aim to preserve nutritional and bioactive molecules more effectively. Ultrasound has shown potential to reduce particle size and enhance physical stability, and combining ultrasound with moderate heat (thermosonication) has been effective in microbial inactivation and reducing enzymatic activity, offering real-world applications for improving the shelf life and quality of plant-based beverages without the need for high temperatures.

📋 中文结构化总结 Chinese Structured Summary

中文

背景:

植物基饮料是谷物、假谷物、种子和豆类的可溶性提取物,外观与牛奶相似。然而,这些产品与普通液态奶在营养成分、感官特性和保质期稳定性等方面存在重要差异。由于乳糖不耐受、牛奶蛋白过敏或生活方式等原因,越来越多的消费者选择此类饮料。为此,人们研究了各种新兴技术,以在不使用高温的情况下解决保质期、营养和乳液稳定性以及感官可接受性问题,因为热处理会降低某些生物活性物质的含量。超声波技术单独使用或与温度结合(热超声处理)可能是改善植物基饮料特性的有效工具。

方法:

不适用——综述类文章。

结果:

本综述详细分析了超声波和热超声处理对杏仁、大豆、椰子、榛子和花生等植物基饮料的物理、生物活性、微生物和感官特性的影响。超声波被定义为频率高于20 kHz的压力波,通过食品系统内的空化作用诱导微气泡的形成。将超声波与适度加热(50–60 °C)结合,即热超声处理,在微生物灭活和降低酶活性方面效果显著。此外,超声波在减小颗粒尺寸和提高物理稳定性方面展现出潜力。

数据摘要:

根据Grand View Research(18)收集的数据,过去五年间,全球以杏仁、大豆、燕麦和坚果为原料的植物基饮料(牛奶替代品)消费量增长了33.5%。该市场在2022年估值为268亿美元,预计2023年至2030年的复合年增长率将超过13.1%(18)。北美在全球植物饮料市场中预计占据最大收入份额,而亚洲预计将成为增长最快的地区,包括中国、印度和韩国等国家(20)。

结论:

超声波技术单独使用或与温度结合(热超声处理)可能是改善植物基饮料特性的有效工具。因此,本综述详细分析了超声波和热超声处理对杏仁、大豆、椰子、榛子和花生等植物基饮料的物理、生物活性、微生物和感官特性的影响。

实际意义:

目前已开发了多种非热技术,如高静压、脉冲电场、微波、辐照和超声波,以应对传统热处理导致的生物活性物质降解问题。这些技术旨在更有效地保留营养和生物活性分子。超声波在减小颗粒尺寸和提高物理稳定性方面展现出潜力,而将超声波与适度加热结合的热超声处理在微生物灭活和降低酶活性方面效果显著,为在不使用高温的情况下延长植物基饮料的保质期和改善其质量提供了实际应用价值。

📖 英文全文 English Full Text

EN

review ISSN 1330-9862 https://doi.org/10.17113/ftb.62.04.24.8624

Ultrasound and Thermosonication as Promising Technologies for Processing Plant-Based Beverages: A Review Dalia M. Sotelo-Lara1 , Genaro G. Amador-Espejo2 , Diego F. Álvarez-Araiza1 , Alondra K. Cordero-Rivera1 , Karla G. Millán-Quintero1 , Rocío Campos-Vega3 and Rita M. Velázquez-Estrada1* National Technological Institute of Mexico / Technological Institute of Tepic, Av. Tecnológico 2595, Col. Lagos del Country, C.P. 63175, Tepic, Nayarit, Mexico 2 CONAHCYT-IPN Applied Biotechnology Research Center, ExHacienda San Juan Molino Carretera Estatal Tecuexcomac-Tepetitla Km 1.5, C.P. 90700, Tlaxcala, Mexico 3 Graduate Program in Food from the Center of the Republic (PROPAC), Research and Graduate Studies in Food Science, School of Chemistry, Universidad Autónoma de Querétaro, Centro Universitario, Cerro de las Campanas S/N, Santiago de Querétaro, Querétaro C.P. 76010, Mexico 1

Copyright© 2024 Authors retain copyright and grant the FTB journal the right of first publication under CC-BY 4.0 licence that allows others to share the work with an acknowledgment of the work’s authorship and initial publication in the journal

*Corresponding author: E-mail: rvelazquez@ittepic.edu.mx 538

SUMMARY Plant-based beverages are water-soluble extracts of cereals, pseudocereals, seeds and legumes that resemble milk in appearance. However, these products have important differences compared to normal liquid milk, such as nutritional composition, sensorial properties and shelf-life stability. Increasing number of consumers are opting for these beverages due to lactose intolerance, milk protein allergies or lifestyle. In this regard, different emerging technologies have been investigated to solve problems such as shelf life, nutritional and emulsion stability as well as sensory acceptability, without using high temperatures since heat treatments decrease the content of some bioactive compounds. Ultrasound technology alone or combined with temperature (thermosonication) could be a valuable tool to improve the properties of plant-based beverages. Therefore, this review provides a detailed analysis of the effect of ultrasound and thermosonication on the physical, bioactive, microbiological and sensory properties of almond-, soybean-, coconut-, hazelnut- and peanut-based beverages, among others. Keywords: plant-based beverages; ultrasound technologies; physicochemical properties

INTRODUCTION The demand for new food products of natural origin has increased due to shifts in consumption patterns and growing health concerns associated with specific products (1). One such category that is gaining popularity is vegetable beverages, often referred to as plant-based “beverages”, derived from sources like soybean, rice, almonds, peanuts or oats. These products face considerable challenges in maintaining physical stability (2). They have garnered attention among consumers pursuing healthier lifestyles because of their rich content of phenolic compounds, unsaturated fatty acids and bioactive compounds such as phytosterols and isoflavones (2). Another notable trend in food consumption is the clean label movement, which advocates for reducing additives in products (3). This has prompted the food industry to explore processing techniques that minimize or eliminate the use of stabilizers, antimicrobials and similar additives. In the case of plant-based beverages, stabilizers like carrageenan or thickener gums are commonly used to prevent phase separation and sedimentation (4). However, the traditional heat treatments applied during food processing can significantly degrade the bioactive compounds of beverages. Various non-thermal technologies such as high hydrostatic pressure, pulsed electric field (5), microwave (6), irradiation (7) and ultrasound (8) have been developed to address this issue. These technologies aim to preserve nutritional and bioactive molecules more effectively (9,10). Non-thermal treatments have shown promise for plant-based beverages such as almond (11), soybean (12) and maize (13), demonstrating minimal impact on particle size and physical stability. Ultrasound, defined as pressure waves with frequencies above 20 kHz, induces the formation of microbubbles through cavitation within the food system (8,14,15). Combining ultrasound with moderate heat (50–60 °C), also known as thermosonication, has been effective in microbial inactivation and reducing enzymatic activity (8,14,15). Furthermore, ultrasound has shown potential to reduce particle size and enhance physical stability (16).

Despite significant research on ultrasound in different food processing areas, such as juices and nectars (8,10,17), comprehensive reviews on its impact specifically on plant-based beverages remain limited (15). Therefore, this review focuses on the current research into the ultrasonic and thermosonic processing of plant-based beverages. It covers consumption trends, market growth and the effects of ultrasound and thermosonication on the physical, bioactive, microbiological and sensory properties of beverages such as almond, soybean, coconut, hazelnut and peanut. Finally, it addresses future challenges and research directions in this evolving field.

PLANT-BASED BEVERAGES AND CONSUMPTION TRENDS Plant-based beverages are defined as aqueous plant extracts that have similar sensory properties to regular fluid milk (15). Beverages can be made from cereals (oats, rice and maize), legumes (soybeans and peas), pseudo-cereals (amaranth and quinoa), seeds (peanuts, sesame and sunflower), nuts (walnuts and almonds) and high-protein or fatty fruits (coconut). Plant-based beverages are obtained by the solid-liquid extraction of raw materials using mechanical force. Breaking down the plant matrix makes it easier to obtain phytochemical and hydrocolloid compounds from it. However, these extracts tend to have large, insoluble and unstable particles (2), which is why they are not physically stable. According to the data collected by Grand View Research (18), the consumption of plant-based beverages (cow’s milk substitutes) based on almonds, soybeans, oats and nuts has increased worldwide by 33.5 % in the last five years. This market was valued at USD 26.80 billion in 2022 and is expected to reach a compound annual growth rate of more than 13.1 % from 2023 to 2030 (18). Soybean-based beverages have been the most consumed plant-based beverages in key markets; however, oat as a raw material was the most sold product from 2019 to 2021 and other sources such as almonds, coconut, rice and soybeans, among others, have been used to a lesser extent. It should be noted that these market reports are mainly from the United States, United Kingdom, Argentina, Belgium, Brazil and Mexico (19). It is estimated that North America will have the largest revenue in the global market of vegetable beverages, although Asia is expected to be the fastest growing region, including countries such as China, India and South Korea (20). Plant-based beverages, a sector of important growth in the food industry, are widely available in local supermarkets worldwide, where the consumer brands that stand out are DREAM, Danone, Daiya Foods, Archer Daniels Midland, Malk Organic, Ripple Foods, The New Barn and Califia Farms (20). It is important to highlight that various authors have associated the increase in the consumption of these plant-based beverages with increased environmental awareness, a preference for low-calorie products, specific diets (veganism) and

medical reasons, including an intolerance to lactose or hypercholesterolaemia (19,20).

Lactose intolerance The National Institutes of Health Consensus Conference defined lactose intolerance as a gastrointestinal symptom that occurs in a person with lactose dyspepsia after consuming a single dose of lactose that is not seen when the person takes a placebo (21). The worldwide prevalence of confirmed cases of lactose intolerance is approx. 57 %. The true prevalence, however, is estimated to be over 65 % and the distribution of cases globally is very uneven, with different incidences in different regions of the world (22). Lactose intolerance is a clinical condition characterised by symptoms attributable to lactose malabsorption such as pain and abdominal distention, flatulence and diarrhoea that occur after lactose consumption. The symptoms of lactose intolerance appear when lactase activity decreases by 50 % (21–23).

Cow’s milk protein allergy Food hypersensitivity or allergy has become a growing global health problem, causing socioeconomic concerns and affecting the quality of life of consumers. Food allergy is defined as an abnormal response of the immune system to the presence of an allergenic protein (24). Any protein can trigger an allergic reaction. There are more than 170 allergenic foods. However, in 2020, the Food and Agriculture Organization of the United Nations (FAO) classified cow’s milk, eggs, shellfish, shrimp, peanuts, tree nuts, wheat and soybeans as the top eight allergenic foods (24,25). Cow’s milk protein allergy (CMA) is the most common food allergy in children under 6 years of age, with a prevalence of 5–15 %. CMA can be defined as any adverse reaction caused by immunological mechanisms mediated by IgE against one or more milk proteins (26,27). Cow’s milk contains approx. 20 proteins with sensitising potential distributed in the whey and casein fractions; the most important of these are β-lactoglobulin, α-lactalbumin, casein allergens and immunoglobulins. CMA is more common in infants because their digestive system is not yet able to process these types of proteins. However, this condition is also observed in adults (28).

Veganism In recent years, there has been an increase in the consumption of vegan diets because of their associated health benefits. These effects include the reduction of the risk of cardiovascular diseases, body mass and cancer and the prevention and/or treatment of type 2 diabetes, among others (29–32). In this sense, it is estimated that the number of people eating a plant-based diet has increased. The Plant-Based October-December 2024 | Vol. 62 | No. 4 539

D.M. SOTELO-LARA et al.: Review of Ultrasound Technologies to Treat Plant-Based Beverages

Foods Association (PBFA) reported that 70 % of people in the United States consumed plant-based foods in 2023, compared to 66 % in 2022 (33). Additionally, the plant-based food market is expected to be worth $22.3 billion by 2029, with an expected compound annual growth rate of 11.82 %. Furthermore, some authors have labelled the vegan diet as the ’most ethical’ due to its benefits for animal welfare. Vegans are characterised by the fact that they do not use any product that contains any element of animal origin or in which animals have been used for manufacturing processes, be it clothing, pharmaceuticals, cosmetics or food (32,34,35). Due to health concerns and increasing trends in dietary choices, there is a shift towards more dairy-free products such as probiotic fermented cereals, dairy-free milk replacers and fruit and vegetable beverages (36–38). In this regard, unconventional technologies that have a potential to provide a plant-based product as an alternative to cow’s milk could be an option.

ULTRASOUND AND THERMOSONICATION The development of non-thermal technologies takes the relationship between food, diet and health into account and aims to use natural ingredients, improve quality and performance, provide functional stability and reduce energy consumption. These technologies include pulsed electric field, high hydrostatic pressure, irradiation, oscillating magnetic field, cold plasma and ultrasound (8,39,40). High-intensity ultrasound is a technology that is commonly used in the food industry. Its main effect is based on the phenomenon of acoustic cavitation, which occurs when ultrasonic waves penetrate a liquid medium and change the pressure, causing the liquid to drop below vapour pressure and bubbles to form. The cavitation bubbles are formed by gas nuclei dissolved in the liquid medium, which begin to grow due to the compression and decompression of the high-intensity waves until they reach a critical size that causes their collapse (41). When cavitation bubbles implode, they generate localised energy accumulation, resulting in regions of very high pressure and temperature that produce waves of shear energy and turbulence (15,16,42) (Fig. 1). The localised sterilisation zones created by ultrasound treatment can reach temperatures of 5000 K and pressures of 100 MPa in microseconds, which can inactivate microorganisms. Cavitation can also lead to the formation of hydroxyl Compression waves Compression

radicals and hydrogen atoms, generated in response to water vapour that sonochemically disintegrates when the bubbles collapse. These substances play a major role in killing microbes because they contain free radicals and electronically excited species that cause the damage. Furthermore, oxidative compounds can cause sublethal damage to cell walls (43). To produce a sterilised product, a combination of sonication and heat was used in a process called thermosonication (11,43). Thermosonication is defined as an ultrasound treatment accompanied by a moderate temperature treatment (45–60 °C). It has been shown that this method eliminates microorganisms faster than ultrasound alone, and in some cases, thermosonication has worked well enough to be used instead of thermal pasteurization for juices with inactivation around 4 log CFU/mL in most cases (44–46). Although most studies have tested thermosonication on fruit juices and nectars (8), it has recently shown positive results on the quality of different beverages based on cereals and seeds. In this sense, Fahmi et al. (47) showed an increase in isoflavones, aglycones and glycosides from a soybean beverage. Similarly, bioactive compounds were released in an almond beverage and thus maintained its sensory appeal (48). Different reviews have described ultrasound equipment and mechanisms used in food production. In this sense, it is important to take some of the new applications of this technology into account, which will be discussed in the following sections.

PLANT-BASED BEVERAGES TREATED BY ULTRASOUND/THERMOSONICATION Plant-based beverages are derived from different plant sources and each plant raw material has unique properties in terms of taste, texture and nutritional composition. The use of ultrasound for plant-based beverages has been studied less than for juices or nectars. In this section a description of several plant-based beverages treated by ultrasound or thermosonication is included. Also, information from different studies is shown in Fig. 2 and Table 1 (11–13,43,47–58).

Almond (Prunus dulcis) The consumption of almond beverages has increased worldwide, but it is still low compared to soybean. In this sense, only a few studies have been carried out in the last eight years. Maghsoudlou et al. (49) were the first to investigate the effect of ultrasound on almond beverages with additives like modified starch, lecithin and agar. The authors treated an almond beverage with ultrasound at 300 W, 20 kHz, 100 % amplitude and times of 0, 2.5 and 5 min. Based on the results, the authors found that there was a decrease in the total soluble solids (approx. 5.5 to 3 %) due to the partial heating of the particles or the absorption of water at high temperature, which caused the swelling of the particles. Moreover, ultrasound treatment affected the the lightness (L*) and October-December 2024 | Vol. 62 | No. 4

Reduction of aerobic mesophiles and enterobacteria Reduction of mesophilic aerobic bacteria

TS and Microwave Microwave (1, 2, 3, 4 and 5 min, 900 W) and TS (28 kHz, 30, 60 and 90 min, 40, 50 and 60 °C) US TS 20 kHz, 500 W, 80 % amplitude (45 °C for 20 min) 35 and 130 KHz, 20 and 40 °C (20, 40 and 60 min)

Higher values of protein 5 log reduction of Escherichia coli and Salmonella typhimurium TS and UV US Coconut with maize additives: high intensity ultrasonic irradiation (20 kHz) US 20 kHz, 130 W, 40, 60 and 100 % amplitude, 2, 6 and 10 min, with 2 and 10 s pulses

TS Reduction of S. enterica and remained below the detection limit (13 days) TS 53 kHz, 70, 80 and 90 °C for 20 min PLANT-BASED MILK No growth of mesophiles aerobes, mould andyeasts was detected Increased antioxidant activity

US and hydrodynamic cavitation US

Ultrasound (200, 300 and 400 W, 20 kHz, 3 min) and hydrodynamic cavitation (6, 8 and 10 bar) - Protein hydrolysis increased. - The particle size decreased Reduction of total mesophilic aerobes, mould and yeasts

US TS 50 °C (4.6, 8.5 and 14.5 W) and 5, 10 and 15 min Greater homogenisation and stability 40 kHz, 600 W, 30, 45 and 60 °C, 10, 20, 30 and 40 min Increased stability of the beverage Better emulsifying and thermal properties

Oatmeal with buttermilk (24 kHz, 20 °C, 15 min, 23 and 154 W)

80 % amplitude for 3 and 5 min (40-45 °C) and 40 % amplitude for 5 min (45 °C) - Lower syneresis index - Reduction in particle size Reduction in particle size Oat with inulin (23 W, 24 kHz with 3 and 15 min, 10 % pulse and 100 % amplitude)

300 W, 20 kHz, 100 % amplitude, for 0, 2.5 and 5 min 20 kHz, 130 W, 80 % amplitude, 8 min and pulse at 6 s

The antioxidant capacity (ABTS and DPPH) increased Decrease in pH and an increase in acidity during storage Increased antioxidant activity

- Increase in total soluble solids - Sensory acceptability No growth of enterobacteria and total aerobic mesophiles was detected Inactivation of E. coli O157:H7 and L. monocytogenes Reduction in particle size The antioxidant capacity (DPPH) increased

Fig. 2. Impact of green technologies on plant-based beverages (US=ultrasound, TS=thermosonication, UV=ultraviolet light)

yellowness (b*); the initial values of L* and b* were 60.4 and -1.8, respectively, while the final values were 82.6 and 1.1, respectively. The viscosity of the product was affected by temperature and showed a pseudoplastic behaviour. The flow index (n) decreased and the consistency coefficient (K) increased. In microbiological analysis, enterobacteria and total aerobic mesophiles were determined, and no growth of microorganisms was detected. Finally, this beverage was sweetened with sugar, stevia and rose water. The sensory analysis measured odour, colour, sweetness, bitterness and overall acceptability. The drink was well accepted by the tasters, suggesting that the use of sugar, stevia and rose water (8.05, 0.55 and 6.38 %, respectively) helped to obtain the best formulation. In this sense, Iorio et al. (50) inactivated Escherichia coli O157:H7 and Listeria monocytogenes in almond beverage with an ultrasound treatment of 20 kHz, 130 W (80 % of amplitude, 8 min and pulse interval at 6 s for E. coli and 80 % amplitude, 2 min and pulse interval at 6 s for L. monocytogenes) and then the samples were stored at 4 °C for 2 weeks. Bacterial inactivation was close to 1 log CFU/mL in both cases. The authors argued that the improvement in shelf life could be related to sublethal injury to pathogens combined with storage under refrigeration.

Recently, Manzoor et al. (11) investigated the physicochemical and biofunctional properties of an almond beverage subjected to thermosonication treatment (40 kHz, 600 W, 30, 45 and 60 °C, 10, 20, 30 and 40 min). The application of thermosonication did not show significant effects on pH, total soluble solids or titratable acidity, but there was an important reduction in particle size measured in the particle surface area D3,2 and volume-weighted mean diameter D4,3 (from 5.22 to 3.96 µm and from 7.02 to 6.46 µm, respectively). Cloudiness was significantly reduced in the pasteurised samples, while it significantly increased in all thermosonicated samples. On the other hand, thermosonication at 40 and 50 °C improved colour parameters b* (yellowness) and L* (lightness) so that the partial precipitation of unstable particles in the suspension can result in coloured compounds, which makes the beverage more sensorially acceptable. Enzymatic analyses showed a more effective reduction of peroxidase and lipoxygenase in thermosonicated samples than in pasteurised samples. Residual lipoxygenase activity was reduced to 5.12 % when treated at 60 °C, 600 W and 40 kHz for 40 min. The peroxidase was reduced to 6.34 % with the same treatment. Total phenol content increased by 4 % at 30 °C and 6.6 % at 45 °C. On the other hand, a decrease of about 5.5 % was October-December 2024 | Vol. 62 | No. 4 541

D.M. SOTELO-LARA et al.: Review of Ultrasound Technologies to Treat Plant-Based Beverages

Table 1. Application of different treatment conditions and their effect on plant-based beverages Beverage Almond Almond Almond Almond Soybean Soybean Soybean Soybean Coconut Coconut Hazelnut Maize Peanut

Whey and oat Whey and oat Rice

Treatment condition Treatment effect Ultrasound (300 W, 20 kHz, Decrease in total soluble solids and colour changes (L* and b*) in some samples. No growth of 100 % amplitude for 0, 2.5 microorganisms. Longer treatments result in less sedimentation of particles. Pseudoplastic and 5 min). Sonotrode of 13 behaviour. A fivefold decrease in the particle size. Adding sugar, stevia and rose water (8.05, mm 0.55 and 6.38 %, respectively) was suggested for the best formulation. Ultrasound (20 kHz, 130 W, A reduction of 3.81 and 4 log CFU/mL of E. coli and L. monocytogenes, respectively (initial load 2 and 8 min, 2, 6, 4 seconds of 5 log CFU/mL). pulse) Thermosonication (600 W, Increased browning index, increased turbidity and reduced particle size with no effect on pH and 40 kHz, 45 and 60 °C, 10, 20, total soluble solids. Lipoxygenase and peroxidase residual activity of 5.12, and 6.34 %, 30 and 40 min) respectively, at 60 °C for 40 min. Complete inactivation of yeast, mould and aerobic mesophilic bacteria after thermosonication (45 °C for 40 min). Higher content of bioactive compounds and antioxidant activity. Increased viscosity with higher temperatures and longer duration. Thermosonication can severely affect sensory scores at higher temperatures and longer duration. Thermosonication (100, Decrease in pH without formation of hydroperoxides but with degradation of fatty acids. 200 and 300 W, 19 kHz at Thermosonication at 50 °C at 14.5 W could favour non-enzymatic browning. Thermosonication 50 °C for 5, 10 and 15 min). treatments at high acoustic power favoured better colour results. Thermosonication causes the Sonotrode of 13 mm loss of some ethyl ester acids. Reduction of only 10 % of phenolic compound content, an increase of total flavonoid content and antioxidant activity. Thermosonication (35 and Higher increase of isoflavones, glycosides and aglycones at 35 than at 130 kHz. Higher content 130 kHz, 20 and 40 °C, 20, of isoflavones, glycosides and aglycones with longer sonication time and higher temperature. 40 and 60 min) Ultrasound (25 kHz, 400 W, Trypsin inhibitor reduction of 52 % with thermosonication (16 min) and 84 % with microwave 1–16 min) and microwave (100 °C for 10 min), the latter having an in vitro protein digestibility of 84.03 % in 16-minute (2450 MHz, 70–100 °C, 2–10 treatment. min) Thermosonication (28 kHz, There is no pH difference. Temperature and time of thermosonication affect product colour. 30, 60 and 90 min, 40, 50 Microwave reduces protein removal, while adequate thermosonication can attenuate the and 60 °C) and microwave effect of microwave. FTIR confirmed conformational deformation of proteins. Increased fat (1, 2, 3, 4 and 5 min, 900 W) content with microwave and thermosonication treatments. Lipoxygenase is sensitive to microwave treatment and trypsin is sensitive to thermosonication. Thermosonication and microwave-assisted treatment enhanced microbial reduction. Increase in viscosity of 68 % after thermosonication (60 °C for 90 min). Ultraviolet light with Quality parameters (pH, protein and colour) remain unchanged. Increase of α-dicarbonyl thermosonication (60 and compounds (glyoxal and methylglyoxal) and advanced glycation end products (Nε-(1105 °C, 10 min and flow carboxymethyl)-l-lysine and Nε-(1-carboxyethyl)-l-lysine) with heat treatment. Reduction of 5 rate of 75 mL/min) log in Escherichia coli and Salmonella typhimurium. Ultrasound irradiation (20 Colour parameters (L*, a*, b* and ΔE) and surface tension did not change. Pseudoplastic kHz) behaviour. Particle size reduction of fat globules with an increase in ζ-potential. Thermosonication (53 kHz, Better emulsifying and thermal properties, higher solubility and surface hydrophobicity, and 70, 80 or 90 °C for 20 min) lower amount of free sulfhydryl groups. Change in the secondary structure of the protein, higher ζ-potential and viscosity, as well as an increase in particle size. Ultrasound (40 and 60 % Slight decrease in pH. Decrease in the colour parameters (L* and b*), particle size and soluble amplitude for 5, 10, 15, 20 protein content. Complete reduction in aerobic mesophilic bacteria, yeast and mould (80 % for and 25 min. Also, 80 % 15 min). Increase in phenolic compounds and antioxidant activity in all treated samples with amplitude for 3, 5, 10 and 15 lower syneresis. min). Sonotrode of 13 mm Thermosonication (20 kHz, There is no difference in pH or titratable acidity. There is an increase in total soluble solids in 500 W, 80 % amplitude, 45 the white maize beverage and a decrease in the purple maize beverage. Reduction of bacteria °C for 20 min). Sonotrode of (mesophilic aerobic 2.59 log CFU/mL and enterobacteria 2.39 log CFU/mL). Inactivation of 18 mm yeasts, moulds and spores. Increased antioxidant activity with higher concentrations of ferulic and chlorogenic acids, but decreased phenolic compounds. Pseudoplastic behaviour in both beverages, with no differences in the consistency coefficient (K) or flow index (n). Ultrasound (200, 300 and Higher total soluble solids content, ζ-potential and pH with a decrease in titratable acidity. 400 W, 20 kHz, 3 min) and Increased a* and h* values and decreased b* and C* values in ultrasound- and pressure-treated pressure (6, 8 and 10 bar) samples. Microbial reduction (1.53 log CFU/mL in aerobic mesophiles, about 2 log CFU/mL in yeast and moulds). Non-Newtonian behaviour by decreasing particle size with ultrasonic intensities (with a better sedimentation rate) and higher pressures. Ultrasound (24 kHz, 0, 3 and Colour, titratable acidity, composition and pH without significant differences. Higher 10 min, 23 and 154 W) antioxidant activity in the ultrasound-treated samples, with higher ABTS content. Ultrasound (23 W, 24 kHz, 3 Decrease in pH and increase in antioxidant activity and acidity during storage. Inhibitory effect and 15 min, 10 % pulse and of angiotensin-converting enzyme activity higher than 50 %. Better acceptance of ultrasound100 % amplitude) -treated beverages than heat-treated ones. Ultrasound (20 kHz, 40, 60 Reduction of Salmonella enterica ATCC 35664 (3 and 1 log CFU/mL), remaining below the and 130 W, 100 % amplitude, detection limit during storage (13 days at 4 °C). 2, 6 and 10 min, with 2 and 10 s pulses)

ABTS=2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) assay, FTIR=Fourier-transform infrared spectroscopy, ATCC=American type culture collection 542 October-December 2024 | Vol. 62 | No. 4 Food Technol. Biotechnol. 62 (4) 538–552 (2024)

observed in samples treated at 60 °C. Similar results were observed for flavonols and flavonoids during thermosonication treatment at 30, 45 and 60 °C. The content of condensed tannins treated with thermosonication ranged from 205.8 to 159.2 µg/g; total antioxidant capacity (TAC), DPPH and hydroxyl radical scavenging activities also increased significantly. Moulds and yeasts as well as aerobic mesophiles were analysed, none of which were detected after treatment at 45 °C for 40 min. With a different objective, Strieder et al. (48) performed phytochemical analysis and determined the composition of fatty acids and volatile organic compounds of thermosonicated almond-based beverages. Thermosonication was carried out at 50 °C using three acoustic powers (4.6, 8.5 and 14.5 W) and time (5, 10 and 15 min). The pH of the almond-based beverage decreased after thermosonication and the lowest values were observed in the beverage treated at 14.5 W. Similarly, a 10 % reduction in phenolic compounds was found in the treated samples compared to the control. The results of antioxidant activity were similar to the control and as for flavonoids, the samples treated at 14.5 W had lower values than the samples treated at the other acoustic powers. The content of oleic, stearic, lauric, palmitic and myristic acids in the almond beverage was determined and acoustic cavitation promoted the reduction of fat globules, resulting in better homogenisation and stability of the samples. Treatment at 50 °C with 14.5 W could promote non-enzymatic browning due to the Maillard reaction. However, the longer time and acoustic power treatments gave better colour results.

Soybean (Glycine max) Soybean is by far the most widely used legume for beverage production. In this regard, many studies have been carried out applying ultrasound and thermosonication. Fahmi et al. (47) applied ultrasound treatments (35 and 130 kHz, 20 and 40 °C, 20, 40 and 60 min) to soybean beverages. They used reversed-phase liquid chromatography to determine the content of isoflavones, including daidzin, genistin and their respective aglycones, daidzein and genistein. A steady increase in the content of isoflavones, glycosides and aglycones was found at both frequencies. In particular, the treatment at 35 kHz showed a more significant increase in isoflavone content than the treatment at 130 kHz. It was also observed that with the increase in sonication time (from 20 to 60 min) and temperature (from 20 to 60 °C), there was a corresponding increase in isoflavone content. This shows a positive correlation between the increase in temperature/time and a higher isoflavone content in soybean beverages; however, the frequency had an opposite effect. With all this and to confirm the behaviour of isoflavones, it is necessary to further investigate ultrasound frequencies, temperature, times and other parameters. More recently, Vanga et al. (51) investigated the effect of ultrasound (25 kHz, 400 W, 1–16 min) and microwaves (2450 MHz, 70–100 °C, 2–10 min) on the structure of soybean

beverages, in vitro digestibility and trypsin inhibitory activity. An incremental trend in trypsin inhibitory activity was observed with increasing duration of ultrasound treatment. Notably, the highest reduction in trypsin inhibitor content was observed at 16 min, reaching 52 %. On the other hand, the use of microwaves surpassed the effect of ultrasound, achieving a reduction of 84 %, especially at 100 °C for 10 min. Digestibility also improved, increasing to 81.38 % after just 4 min of ultrasound treatment. This trend persisted with increasing duration of treatment, eventually obtaining a digestibility percentage of 84.03 %. The effect on the protein structure was analysed. After 16 min ultrasound treatment, there was a loss of α-helix and an increase in β-sheet in the proteins, showing that ultrasound can have an effect on the molecular conformation of soybean proteins. In this context, Kumar et al. (12) performed microwave (1, 2, 3, 4 and 5 min; 900 W) and thermosonication (28 kHz; 30, 60 and 90 min; 40, 50 and 60 °C). The authors evaluated different parameters such as the composition of proteins, fat and total soluble solids, viscosity, trypsin inhibitory activity and lipoxygenase activity in soybean beverages. The results indicated that thermosonication performed better than the ultrasound alone, but that microwave treatment gave even better results. The inactivation rate constants for the trypsin and lipoxygenase inhibitory activities were found to be 0.2034 and 0.3232 min –1, respectively. Lipoxygenase was more susceptible to microwave inactivation than to thermosonication, while conversely trypsin was more susceptible to thermosonication. With thermosonication, protein content, lipids, total soluble solids and viscosity increased and were affected by microwave time. The inactivation rate constants of trypsin and lipoxygenase inhibitory activities were 0.2034 and 0.3232 min –1, respectively. These results showed that lipoxygenase was more susceptible to inhibition by microwaves than by thermosonication. Otherwise, trypsin was more susceptible to thermosonication. Fourier transform infrared (FTIR) analysis confirmed the conformational change of the proteins and the enhancement of molecular interactions with a significant effect on viscosity (which increased up to 68 % after thermosonication treatments). Finally, the total mesophilic aerobic bacteria count showed a significant decrease. In contrast, Park et al. (52) investigated the effect of ultraviolet light (UVC) with thermosonication on Ecklonia cava extract to provide an alternative process and prevent the formation of advanced glycation end products in processed soybean-based beverages. A noteworthy result was the 5-log reduction of Escherichia coli and Salmonella typhimurium in the soybean-based beverage. On the other hand, the study showed an increase in α-dicarbonyl compounds (glyoxal and methylglyoxal) and advanced glycation end products (Nε-(1-carboxymethyl)-l-lysine and Nε-(1-carboxyethyl)-l-lysine) in soybean-based beverages after pasteurisation. This finding raises questions about the possible negative effects of traditional pasteurisation methods on the nutritional October-December 2024 | Vol. 62 | No. 4 543

D.M. SOTELO-LARA et al.: Review of Ultrasound Technologies to Treat Plant-Based Beverages quality and safety of soybean-based beverages. Furthermore, it was observed that ultraviolet light together with thermosonication, unlike pasteurisation, resulted in a decrease in α-dicarbonyl compounds and advanced glycation end products, which could be a potential advantage of the UVC with thermosonication in maintaining the nutritional quality of this type of beverages. Similarly, ultraviolet light and thermosonication of Ecklonia cava extract improved the antioxidant activity and preserved the quality parameters.

Coconut (Cocos nucifera L.) Only a few studies of the application of ultrasound and thermosonication on coconut-based products have been published. Lu et al. (53) presented the first study of a coconut-based beverage treated by ultrasound. A system consisting of a coconut emulsion (glycerol monostearate as an emulsifier) with different corn additives (corn kernels and starch with different amylose content) was tested with a high-intensity ultrasonic irradiation treatment (20 kHz). The physicochemical properties varied depending on the type of corn starch and the conditions applied. The ultrasound treatments had no effect on the colour. Emulsion stability and structural properties were analysed and compared between the emulsions. The coconut beverage with corn kernels was similar to the coconut beverage with high amylose corn starch, but the highest stability was obtained with high amylopectin content. After ultrasound treatment, it was found that the particle size was smaller than that of the untreated beverage and the particles had a monomodal size distribution. On the other hand, the electronegativity improved. However, ultrasound did not modify the rheological behaviour, which appeared as a pseudoplastic fluid. More recently, Sun et al. (54) investigated the effect of ultrasound treatment (40 W/L, 53 kHz) combined with preheating (70, 80 or 90 °C for 20 min) on the physicochemical properties and structural characteristics of coconut globulin and coconut beverage. The ultrasound combined with preheating (90 °C) conferred improved emulsifying and thermal properties to coconut protein ande confirmed higher solubility (45.2 to 53.5 %), lower amount of free sulfhydryl groups (33.24 to 28.05 µmol/g) and higher surface hydrophobicity (7658.6 to 10 815.1). Moreover, FTIR and SEM microscopy showed changes in the secondary structure of the protein. There was also an increase in the zeta potential (–11 to –23 mV) due to the change in the physicochemical properties of the protein. On the contrary, a decrease in the thermal aggregation rate (148.5 to 13.4 %) and an increase in viscosity (126.9 to 1103.0 mPa∙s) were observed, all indicating that ultrasound combined with preheating can improve thermal stability.

Hazelnut (Corylus avellana) Hazelnut-based beverages are less common than other plant-based products, mainly because of the allergies associated with this nut. In this sense, the number of studies of 544

ultrasound or thermosonication applications on hazelnut-based beverages is scarce. Atalar et al. (43) applied thermosonication treatments (80 and 40 % amplitude for 3 and 5 min, 40–45 °C) to hazelnut-based beverages. The results obtained showed a lower syneresis index (%) in thermosonicated samples than in the conventional heat treatment, suggesting an improvement of its structural properties. In terms of rheological properties, the thermosonication caused a reduction in the average particle size of the samples (about 20 % of the 80 % reported for the 5-minute treatment). The soluble protein content also decreased significantly. For colour determination, under specific treatment conditions (10 min at 40 % amplitude and 5 min at 60 and 80 % amplitude), there was a decrease in the values of L* and b*, but the value of a* did not change in the treated samples. For the microbial inactivation, total counts of aerobic mesophiles, and moulds and yeasts were 5.98 and 3.65 log CFU/mL, respectively (80 % after 15 min of treatment). An increase in phenolic compounds and antioxidant activity was also observed in all treated samples, mainly related to plant cell wall breakage, with the highest value obtained in the 60 % treatment for 25 min.

Maize (Zea mays) Only one study has been published on the use of thermosonication in maize-based beverages. Rodriguez-Salinas et al. (13) investigated the effect of thermosonication (20 kHz, 500 W, 80 % amplitude and 45 °C for 20 min) on maize beverages and evaluated the colour, microbiological quality and physicochemical and nutraceutical properties of white and purple corn beverages. The results showed that the lightness values (L*) between thermosonicated white and purple maize beverages showed small differences. On the other hand, a* and b* parameters increased in thermosonicated samples and tended towards the colours green and yellow. Moreover, a significant reduction in total aerobic mesophiles (from 6.96 to 4.37 log CFU/mL), enterobacteria (5.45 to 3.06 log CFU/mL) and yeast and moulds (not detected) was observed. Regarding bioactive compounds, an increase in antioxidant activity and a higher concentration of ferulic and chlorogenic acids were detected, but a decrease in phenolic compounds was observed in both beverages, without condensed tannins and a higher content of total flavonoids in the thermosonicated purple maize beverage. Finally, the viscosity of the white and purple maize beverages showed pseudoplastic behaviour according to the power law. There were no significant differences in the consistency coefficient (K) or the flow index (n) between the two beverages.

Peanut (Arachis hypogaea) As with hazelnuts and other nuts, the use of peanuts in beverages is restricted due to high number of allergies. For this reason, the number of published studies on the use of ultrasound in this type of matrix is scarce. Salve et al. (55) applied ultrasound in peanut beverages at different intensities October-December 2024 | Vol. 62 | No. 4

Food Technol. Biotechnol. 62 (4) 538–552 (2024) (200, 300 and 400 W for 3 min) with increasing pressure (0.6, 0.8 and 1 MPa). The sonicated samples showed a higher total soluble solids content, higher protein hydrolysis and pH than the untreated samples. On the other hand, the treated samples showed a decrease in titratable acidity. The analysis of the ζ-potential of the ultrasonic treatments showed an increase from –27.6 to –30 mV, showing higher stability. However, an intensity of 400 W led to instability with a ζ-potential of –11 mV and resulted in the formation of aggregates. The particle size decreased with increasing ultrasonic intensity and pressure (0.29 to 0.02 µm), while the behaviour of all samples was a non-Newtonian fluid. The samples treated with powers of 200, 300 and 400 W showed the best sedimentation index since there was no phase separation, proving that the increase in ultrasonic intensity did not affect the stability of the product. The evaluation of the colour of the samples showed no significant differences in the L* value between the ultrasound-treated and untreated beverages, except for the one treated with a power intensity of 300 W, which was slightly darker than the other ultrasound-treated samples. The colour analysis showed an increase in the a* value with different treatment methods, a decrease in the b* and C* values with increasing intensity and a slight increase in the hue value of the samples treated with ultrasound and pressure. Finally, a microbiological analysis of total aerobic mesophiles, and yeast and moulds was performed, which showed a reduction of 1.53 log and about 2 log, respectively.

Other plant-based beverages Another interesting group that has developed in the last few years is the beverage based on the mixture of plant and whey, which is offered as a reuse of whey (reducing its polluting effect) and containing a protein with excellent nutritional quality. It is also suitable for those who do not follow a 100 % vegetarian diet. In this way, Herrera-Ponce et al. (56) used ultrasound treatments (24 kHz; 0, 3 and 10 min; 23 and 154 W) on whey and oat (Avena sativa L.) beverages (50:50) to verify the quality and benefits of the products. Colour, titratable acidity and pH value showed no significant differences. In this sense, no significant differences were found in the proximate analyses (water, fat, protein, ash and carbohydrates) between the two ultrasonic powers used. However, there was a difference between the sonicated and heat-treated samples. The antioxidant capacity was higher in the sonicated samples than in the pasteurised ones, with ABTS giving better results than DPPH. In another study published by the same research group, a beverage from oat and whey containing inulin (1 and 2 %) was treated with ultrasound (23 W, 24 kHz, 3 and 15 min, 10 % pulse and 100 % amplitude) and they found a decrease in pH and an increase in acidity during storage. On the other hand, an increase in antioxidant activity was observed in most treatments. When the inhibitory effect of the angiotensin-converting enzyme activity was evaluated, it was found that all treatments were above 50 % of the inhibitory effect and that the best treatment was 1 % inulin

and 15-min ultrasound with 14 days of storage with 79.63 % inhibition (57). A popular food matrix in Asia that is more commonly fermented is rice-based beverages. In this sense, Campaniello et al. (58) evaluated the antibacterial effect of ultrasound treatments (20 kHz; 130 W; 40, 60 and 100 % amplitude; 2, 6 and 10 min; with 2 and 10 pulses) on the inactivation of Salmonella enterica ATCC 35664. The microorganism was inoculated in a rice (Oryza sativa) beverage at two cell counts (8 and 5 log CFU/mL). After treatment, a reduction of 3 and 1 log CFU/mL was obtained, respectively. S. enterica remained below the detection limit for 13 days at 4 °C. A large number of plant-based beverages have been developed using ultrasound and thermosonication treatments and they represent an opportunity for a growing market. In all cases, the products developed were determined on a laboratory scale, which opened up the opportunity for higher production volumes, while facing the associated challenges.

ULTRASOUND AND THERMOSONICATION EFFECTS Ultrasound treatment can increase, decrease or inactivate various processes through specific mechanisms of action such as thermal mechanisms (generation of heat or mechanical energy) and non-thermal mechanisms (cavitation, condensation and rarefaction, formation of free radicals and micromechanical shocks), as described in the chapter on ultrasound and thermosonication. Therefore, the effects of ultrasound and thermosonication on quality (physicochemical, microbial and enzymatic) and stability (particle size, sedimentation and fatty acid reactivity) are discussed in the following section.

Physicochemical properties Different physicochemical properties, such as pH, particle size and colour, have been studied in plant-based beverages. Maghsoudlou et al. (49) reported an increase in total soluble solids in an almond beverage due to partial cooking of the particles or the absorption of water at high temperatures, leading to swelling of the particles. The researchers attributed the decrease in modified starch in sonicated samples to cell wall breakdown and polysaccharide hydrolysis, including modified starch, caused by the shear force due to acoustic cavitation. The titratable acidity decreased because of the change in particle charge caused by cavitation. As a result, the negative γ-potential charge increased even more, leading to an increase in pH (55). Colour is an important attribute that affects consumer perception and is a visual indicator of the quality of a beverage (15). The scattering of particles in the beverage increases with decreasing size during ultrasonic treatment, resulting in higher light scattering and lightness values. Similar results have been found in the thermosonicated almond-based beverages, where parameters such as b* (yellowness) and L* October-December 2024 | Vol. 62 | No. 4 545

D.M. SOTELO-LARA et al.: Review of Ultrasound Technologies to Treat Plant-Based Beverages (lightness) are improved by treatment at temperatures of 40 and 50 °C, where coloured compounds can be produced by the partial precipitation of unstable particles in the suspension, making the beverage more sensorially acceptable (11).

Structural modifications Ultrasound treatment can modify protein structure and expose some of their internal hydrophilic parts (59). In this sense, Režek Jambrak et al. (60) applied ultrasound treatments (20 kHz, 43–48 W/cm2, 15–30 min) to whey protein and found that the molecular mass of proteins decreased. The authors also observed changes in the tertiary structure of proteins, which led to an increase in charged groups (NH4+ and COO –) and increased water-protein interactions. Therefore, ultrasound helps to improve the water retention of beverages. On the other hand, ultrasound reduces the size of fat globules due to the implosion of bubbles generated by acoustic cavitation, which produces high-intensity shock waves (61). This leads to homogenisation, resulting in a higher number of fat globules per unit volume but of a smaller size. It has also been reported that the decrease in fat globule size depends on two factors: time and amplitude (61). The ultrasound treatment can increase the solubility of organic or inorganic salts, leading to a decrease in ash content (62).

longer ultrasonic time and temperature, while it is higher at shorter ultrasonic time and temperature (11).

Enzymatic inactivation An enzyme is a protein whose structure can be affected by chemical (acidity, organic solvents, alkalinity, etc.) and physical factors (irradiation, heating, microwave, etc.). Its activity is determined by the degree of exposure of the active site located in the centre of the enzyme. Controlled conformational changes can increase the enzyme activity, while more severe processing conditions can reduce the catalytic activity of the enzyme (66,67). Cavitation, the formation of free radicals and localised high temperature and pressure conditions produced by ultrasound are considered the main mechanisms causing enzyme inactivation. Sonication could cause the breaking of the hydrogen bonds and the van der Waals interactions in the polypeptide chain, which favours the modification of the secondary structure of the enzyme and consequently causes the loss of biological activity of the enzyme (68–70). This technology has been shown to have positive effects on enzyme activity by causing an acceleration of enzymatic reactions due to its physical modification method in which the formation of free radicals and shear forces act on the enzyme structure and promote interactions with the substrate (71,72).

Bioactive compounds Phenolic compounds are found in the vacuole in soluble form or attached to the cell wall as pectin, cellulose, hemicellulose and lignin (48). The increase in phenolic content after ultrasound treatment can be attributed to the disruption of cell walls, which could facilitate the release of the bound phenolics (63). An increase in bioactive compounds by thermosonication could be due to the release of secondary metabolites because the mechanical rupture of cell walls is enhanced by cavitation (11). Ghasemzadeh et al. (64) reported that an acoustic wave disrupts the biological cell and promotes the release of cell contents. However, higher thermosonication temperatures can reduce the content of these compounds due to thermal degradation. Moreover, the acoustic energy provided by thermosonication can lead to these increases and decreases in antioxidant capacity, as well as favour the bioavailability of bioactive compounds in the sonicated medium and promote the production of hydroxyl radicals that can oxidize phenolic compounds in the same way when high temperatures and power are used, resulting in bubble collapse (17). The decrease in bioactive compounds during thermosonication at high temperatures could be associated with processing parameters including treatment time, temperature and power (65). On the other hand, a decrease in the formation of free radicals is associated with an increase in antioxidant activities, but a high amount of free radicals for a long time can inhibit the antioxidant activity (65). Similarly, the free radical scavenging activity has been reported to be lower at 546

Sedimentation index, particle size and rheological properties Sedimentation refers to the movement of particles or macromolecules in a field of inertia. Settling mechanisms can be explained by Stokes’ law, in which the settling particle velocities and densities interact with the dispersing medium (43). In this case, different types of behaviour can occur. In one, the sedimentation of larger particles with different densities between the particles and the continuous phase is accelerated. On the other hand, particles with a density higher than the continuous phase will sediment over time under the force of gravity. In liquid foods such as milk, sedimentation becomes a quality problem if it is excessive (73). Due to the cavitation effect, thermosonication reduces the sedimentation rate by releasing intracellular compounds that increase the mean viscosity (43). In peanut-based beverages treated with ultrasound (20 kHz at 200, 300 and 400 W), no phase separation was observed, which shows that the increase in ultrasound intensity does not affect the stability of the particles, as evidenced by the sedimentation index values based on the reduction in the size of the particles and thus the facilitation of intermolecular reactions. In addition, it can cause the denaturation of peanut proteins, promote the unfolding of peanut protein molecules by exposing their active sites and increase the hydrophobicity of the molecular surfaces (55). On the other hand, particle size is affected because ul­ trasound disintegrates plant and beverage particles by October-December 2024 | Vol. 62 | No. 4

low-frequency acoustic cavitation (43). Microbubbles are generated and constantly collapse near the interface, creating localised turbulence. The acoustic waves, high shear force generated by the microflow and high-pressure shock can cause larger droplets (53). Rheology is a fundamental part of the characterisation of food products, which is defined as the science that studies the parameters of deformation of matter, which vary depending on the processing of the food transformation until the final product is manufactured (74). Maghsoudlou et al. (49) used the ultrasound on almond-based beverages and found that the flow index (n) decreased while the consistency coefficient (K) increased; this could be related to the shrinkage of the swollen starch and network destruction caused by depolymerisation, carbohydrate or thermal coagulation under ultrasonic treatment (54). However, thermosonication does not affect viscosity, but it may improve viscosity by aiding distribution and reducing the size of hydrocolloids (13).

Microbial inactivation Several mechanisms explain the inactivation effect of thermosonication on microorganisms, including the phenomenon of cavitation, which is able to damage the cell wall and membrane of microorganisms by forming pores (sonopo­ ration). Sonoporation is also known as cell sonication, which creates bubbles and causes acoustic cavitation, thus modifying the permeability of the cell plasma membrane (15). This leads to the cell disruption and consequently to a loss of intracellular content (14). Ultrasound perforates the cell membranes of microorganisms and the extrusion of the intracellular matrix generates free radicals that ultimately kill the microorganisms (75). Cavitation also helps to inhibit the growth of microorganisms by inactivating the enzymatic activity of mitochondria (76). The morphology, such as the type, shape or diameter of the microorganism, affects the efficiency of microbial inactivation, making the effect of thermosonication different for different microorganisms. In this sense, Gram-negative bacteria are less resistant than Gram-positive bacteria. Due to their peptidoglycan coating, bacterial spores and moulds are more resistant to ultrasound than vegetative bacteria (76).

Fatty acids Cereals such as oats, legumes such as soybeans, walnuts, hazelnuts and almonds and some seeds (such as sunflower or sesame), which are also used for plant-based beverages, are rich in saturated and polyunsaturated fatty acids, some of which consist of more than 90 % polyunsaturated fatty acids (39). Lipid oxidation by thermosonication may be due to thermal and sonochemical degradation. The high temperatures generated during thermosonication and the free radicals produced may favour the oxidation of lipids. However, although the microbubbles generated by cavitation can promote lipid oxidation, short retention times and reduced heat

exposure can prevent the formation of oxidizing compounds during thermosonication. On the other hand, acoustic cavitation leads to better homogenisation and stability in samples containing lipids by promoting the reduction of fat globules (48). It should be noted that the thermosonicated hazelnut beverage did not favour the formation of hydroperoxides, although it showed degradation of fatty acids (48). Based on the microbial and physicochemical results obtained, the ultrasound application has been shown to be suitable for food processing, as it offers the possibility of combining particle reduction with microbial inactivation in one piece of equipment, which can lead to important reduction in time and cost for food processors.

CHALLENGES AND FUTURE WORK Today’s consumers are driving the food industry to develop a range of innovative products that offer not only sensory and nutritional properties, but also functionality and affordability. The future of the beverage market will therefore depend on offering healthy lifestyle choices and taking the prevalence of food allergies and intolerances into account. In this regard, the challenge with plant-based beverages is not only in the plant-derived matrix and the extraction process, but also in the technique used to preserve them while maintaining the quality and biological functionality of the compounds. In this sense, ultrasound and thermosonication have been shown to offer several advantages for plant-based beverages. Additionally, these technologies could be useful as pre-fermentation processes for these plant-based beverages, thus producing high yielding and high-quality fermented products (57,76). In addition, the process scaling, where equipment designers make significant improvements to increase processing volume, is probably the biggest challenge for ultrasound and thermosonication applications and their successful market entry. Nevertheless, the industry continues to operate in a niche production environment. The same line of research could also include the possible combination with other technologies such as ultraviolet light, microwave and filtration, among others. Finally, the food industry is trying to adopt environmentally friendly technologies, such as thermosonication, which are sustainable in processing by reducing energy and water consumption.

CONCLUSION Society’s growing demand for non-dairy products and increasing competition in the food industry emphasise the potential of cutting-edge technologies like ultrasound and thermosonication as suitable replacements for traditional plant-based beverage processing methods. These technologies not only improve the quality of these beverages but also enable the production of clean-label products. Although there are no ultrasound devices that can treat large volumes, the designs show that this barrier could be broken in the near October-December 2024 | Vol. 62 | No. 4 547

D.M. SOTELO-LARA et al.: Review of Ultrasound Technologies to Treat Plant-Based Beverages future. Additionally, because they are sustainable, they comply with environmental standards and open the door to future commercial applications that promote ecological and industrial goals.

📖 中文全文 Chinese Full Text

中文

# 超声与热超声技术作为植物基饮料加工中的有前景技术:综述

## 摘要

植物基饮料是谷物、伪谷物、种子和豆类的可溶性水提取物,外观与牛奶相似。然而,与普通液态奶相比,这些产品在营养成分、感官特性和保质期稳定性方面存在重要差异。由于乳糖不耐受、牛奶蛋白过敏或生活方式选择,越来越多的消费者选择此类饮料。在此背景下,人们研究了各种新兴技术来解决保质期、营养和乳液稳定性以及感官可接受性等问题,同时避免使用高温处理,因为热处理会降低某些生物活性化合物的含量。超声技术单独使用或与温度结合使用(热超声)可能是改善植物基饮料性能的有效工具。因此,本综述详细分析了超声和热超声对杏仁、大豆、椰子、榛子和花生等饮料的物理、生物活性、微生物和感官特性的影响。

**关键词:** 植物基饮料;超声技术;理化特性

## 引言

由于消费模式的转变以及与特定产品相关的健康问题日益突出,人们对新型天然食品的需求不断增加(1)。其中一类日益受欢迎的产品是植物性饮料,通常称为植物基"饮料",来源于大豆、大米、杏仁、花生或燕麦等原料。这些产品在维持物理稳定性方面面临相当大的挑战(2)。由于富含酚类化合物、不饱和脂肪酸以及植物甾醇和异黄酮等生物活性物质,这些产品吸引了追求健康生活方式的消费者的关注(2)。食品消费中的另一个显著趋势是清洁标签运动,倡导减少产品中的添加剂使用(3)。这促使食品行业探索能够最大限度减少或消除稳定剂、抗菌剂及类似添加剂使用的加工技术。

在植物基饮料中,卡拉胶等稳定剂或增稠胶通常用于防止相分离和沉淀(4)。然而,食品加工过程中应用的传统热处理会显著降解饮料中的生物活性化合物。为解决这一问题,已开发出多种非热技术,如高静压、脉冲电场(5)、微波(6)、辐照(7)和超声(8)。这些技术旨在更有效地保留营养和生物活性分子(9,10)。非热处理在杏仁(11)、大豆(12)和玉米(13)等植物基饮料中显示出良好效果,对粒径和物理稳定性的影响极小。

超声定义为频率高于20 kHz的压力波,通过空化作用在食品体系中诱导微泡的形成(8,14,15)。将超声与适度加热(50–60°C)结合,即热超声,在微生物灭活和降低酶活性方面效果显著(8,14,15)。此外,超声在减小粒径和提高物理稳定性方面显示出潜力(16)。

尽管超声在不同食品加工领域(如果汁和果浆)(8,10,17)已有大量研究,但专门针对植物基饮料影响的综述仍然有限(15)。因此,本综述聚焦于植物基饮料超声和热超声加工的最新研究进展,涵盖消费趋势、市场增长以及超声和热超声对杏仁、大豆、椰子、榛子和花生等饮料的物理、生物活性、微生物和感官特性的影响。最后,本文还探讨了该新兴领域未来的挑战和研究方向。

## 植物基饮料与消费趋势

植物基饮料被定义为具有与常规液态奶相似感官特性的植物水提物(15)。饮料可由谷物(燕麦、大米和玉米)、豆类(大豆和豌豆)、伪谷物(苋菜和藜麦)、种子(花生、芝麻和向日葵)、坚果(核桃和杏仁)以及高蛋白或高脂肪水果(椰子)制成。植物基饮料是通过对原料进行固液提取,利用机械力破坏植物基质,从而更容易获得植物化学物质和水胶体化合物。然而,这些提取物往往含有较大、不溶且不稳定的颗粒(2),因此物理稳定性较差。

根据Grand View Research(18)收集的数据,过去五年全球以杏仁、大豆、燕麦和坚果为原料的植物基饮料(牛奶替代品)消费量增长了33.5%。该市场在2022年估值为268亿美元,预计2023年至2030年的复合年增长率将超过13.1%(18)。

大豆基饮料一直是主要市场中消费量最大的植物基饮料,但2019年至2021年间,燕麦作为原料成为最畅销的产品,杏仁、椰子、大米和大豆等其他来源的使用相对较少。需要指出的是,这些市场报告主要来自美国、英国、阿根廷、比利时、巴西和墨西哥(19)。预计北美将在全球植物饮料市场中占据最大收入份额,而亚洲预计将成为增长最快的地区,包括中国、印度和韩国等国家(20)。

植物基饮料是食品行业中一个重要增长领域,在全球各地的超市中广泛销售,其中突出的消费品牌包括DREAM、Danone、Daiya Foods、Archer Daniels Midland、Malk Organic、Ripple Foods、The New Barn和Califia Farms(20)。

值得强调的是,多位作者将植物基饮料消费量的增加与环境意识增强、对低热量产品的偏好、特定饮食(纯素食主义)以及乳糖不耐受或高胆固醇血症等医学原因联系起来(19,20)。

### 乳糖不耐受

美国国立卫生研究院共识会议将乳糖不耐受定义为:一名乳糖消化不良患者在摄入单剂量乳糖后出现的胃肠道症状,而在摄入安慰剂时不会出现此类症状(21)。

全球确诊乳糖不耐受病例的患病率约为57%。然而,真实患病率估计超过65%,且全球病例分布极不均匀,不同地区的发病率存在差异(22)。乳糖不耐受是一种临床病症,其特征是乳糖吸收不良引起的可归因症状,如腹痛和腹胀、胀气和腹泻,在摄入乳糖后出现。

当乳糖酶活性降低50%时,乳糖不耐受症状即会出现(21–23)。

### 牛奶蛋白过敏

食物超敏反应或过敏已成为日益严重的全球健康问题,引起社会经济方面的关注并影响消费者的生活质量。食物过敏被定义为免疫系统对过敏原蛋白的异常反应(24)。任何蛋白质都可能引发过敏反应。目前已知的致敏食物超过170种。然而,2020年联合国粮食及农业组织(FAO)将牛奶、鸡蛋、贝类、虾、花生、坚果、小麦和大豆列为八大主要致敏食物(24,25)。

牛奶蛋白过敏(CMA)是6岁以下儿童最常见的食物过敏,患病率为5–15%。CMA可定义为由IgE介导的免疫机制对一种或多种牛奶蛋白引起的任何不良反应(26,27)。牛奶含有约20种具有致敏潜力的蛋白质,分布于乳酪蛋白和乳清蛋白组分中,其中最重要的是β-乳球蛋白、α-乳白蛋白、酪蛋白过敏原和免疫球蛋白。CMA在婴儿中更为常见,因为他们的消化系统尚未能处理这些类型的蛋白质。然而,这种情况在成人中也有观察到(28)。

### 纯素食主义

近年来,由于纯素食饮食对健康的益处,其消费量有所增加。这些益处包括降低心血管疾病风险、体重和癌症风险,以及预防和治疗2型糖尿病等(29–32)。

在此背景下,估计选择植物性饮食的人数有所增加。植物基食品协会(PBFA)报告称,2023年美国70%的人消费植物基食品,而2022年为66%(33)。此外,预计到2029年,植物基食品市场价值将达到223亿美元,预期复合年增长率为11.82%。

此外,一些作者将纯素食饮食称为"最合乎伦理的"饮食,因为它有利于动物福利。纯素食者的特征是不使用任何含有动物成分或在制造过程中使用了动物的产品,无论是服装、药品、化妆品还是食品(32,34,35)。

由于健康问题和饮食选择的日益增长趋势,人们正在转向更多无乳制品,如益生菌发酵谷物、无乳奶替代品以及果蔬饮料(36–38)。在此背景下,具有潜力提供植物基产品作为牛奶替代品的非传统技术可能是一个选择。

## 超声与热超声

非热技术的发展考虑了食品、饮食与健康之间的关系,旨在使用天然成分、提高质量和性能、提供功能稳定性并降低能耗。这些技术包括脉冲电场、高静压、辐照、振荡磁场、冷等离子体和超声(8,39,40)。

高强度超声是食品工业中常用的一项技术。其主要效应基于声空化现象,当超声波穿透液体介质并改变压力时,液体压力降至蒸汽压以下,从而形成气泡。空化气泡由溶解在液体介质中的气体核形成,由于高强度波的压缩和膨胀作用,气泡开始生长,直至达到临界尺寸后崩溃(41)。当空化气泡内爆时,会产生局部能量积累,形成极高压力和温度的区域,产生剪切能波和湍流(15,16,42)(图1)。

超声处理产生的局部灭菌区域可在微秒内达到5000 K的温度和100 MPa的压力,从而灭活微生物。空化还可导致羟基自由基和氢原子的形成,这些物质是在气泡崩溃时水蒸气发生声化学分解而产生的。这些物质在杀灭微生物方面发挥重要作用,因为它们含有自由基和电子激发态物质,可造成细胞壁的亚致死损伤(43)。

为生产灭菌产品,将超声与加热结合使用,这一过程称为热超声(11,43)。

热超声定义为在适度温度(45–60°C)下进行的超声处理。研究表明,该方法比单独使用超声更快地灭活微生物,在某些情况下,热超声的效果足以替代果汁的热巴氏灭菌,在大多数情况下可实现约4 log CFU/mL的灭活率(44–46)。尽管大多数研究在果汁和果浆上测试了热超声(8),但最近的研究表明,它对谷物和种子类饮料的品质产生了积极影响。在此方面,Fahmi等(47)展示了大豆饮料中异黄酮、苷元和糖苷含量的增加。同样,杏仁饮料中生物活性化合物得以释放,从而保持了其感官吸引力(48)。

不同的综述已描述了食品生产中使用的超声设备和机制。在此方面,考虑该技术的一些新应用很重要,这将在以下各节中讨论。

## 经超声/热超声处理的植物基饮料

植物基饮料来源于不同的植物原料,每种植物原料在口感、质地和营养成分方面具有独特的特性。超声在植物基饮料中的应用研究少于在果汁或果浆中的应用。本节介绍了几种经超声或热超声处理的植物基饮料。此外,图2和表1展示了不同研究的信息(11–13,43,47–58)。

### 杏仁(Prunus dulcis)

全球杏仁饮料的消费量有所增加,但与大豆相比仍然较低。在此方面,过去八年仅进行了少数研究。Maghsoudlou等(49)率先研究了超声对添加改性淀粉、卵磷脂和琼脂的杏仁饮料的影响。作者用超声在300 W、20 kHz、100%振幅下处理杏仁饮料,处理时间分别为0、2.5和5分钟。根据结果,作者发现总可溶性固体含量有所下降(约从5.5%降至3%),这是由于颗粒的部分加热或高温下水分吸收导致颗粒膨胀所致。此外,超声处理影响了亮度(L*)和黄度(b*);L*和b*的初始值分别为60.4和-1.8,而最终值分别为82.6和1.1。产品的粘度受温度影响,表现出假塑性行为。流动指数(n)降低,稠度系数(K)增加。在微生物学分析中,检测了肠杆菌和总需氧中温菌,未发现微生物生长。最后,该饮料用糖、甜菊糖和玫瑰水进行甜味处理。感官分析测量了气味、颜色、甜度、苦度和整体可接受性。该饮料获得了品评员的良好接受,表明使用糖、甜菊糖和玫瑰水(分别为8.05%、0.55%和6.38%)有助于获得最佳配方。

在此方面,Iorio等(50)在杏仁饮料中灭活大肠杆菌O157:H7和单核细胞增生李斯特菌,超声处理条件为20 kHz、130 W(80%振幅、8分钟、脉冲间隔6秒用于大肠杆菌;80%振幅、2分钟、脉冲间隔6秒用于单核细胞增生李斯特菌),然后将样品在4°C下储存两周。两种情况下细菌灭活率均接近1 log CFU/mL。作者认为,保质期的改善可能与病原体的亚致死损伤结合冷藏储存有关。

最近,Manzoor等(11)研究了经热超声处理(40 kHz、600 W、30、45和60°C、10、20、30和40分钟)的杏仁饮料的理化和生物功能特性。热超声的应用对pH、总可溶性固体或可滴定酸度未显示出显著效果,但在颗粒表面积D3,2和体积加权平均直径D4,3方面粒径显著减小(分别从5.22降至3.96 µm和从7.02降至6.46 µm)。巴氏灭菌样品的浊度显著降低,而所有热超声处理样品的浊度显著增加。另一方面,40和50°C下的热超声改善了颜色参数b*(黄度)和L*(亮度),因此悬浮液中不稳定颗粒的部分沉淀可产生有色化合物,使饮料在感官上更易被接受。酶学分析显示,热超声处理样品中过氧化物酶和脂肪氧合酶的减少比巴氏灭菌样品更有效。在60°C、600 W和40 kHz下处理40分钟时,残余脂肪氧合酶活性降至5.12%。相同处理条件下,过氧化物酶降至6.34%。30°C时总酚含量增加4%,45°C时增加6.6%。另一方面,60°C处理的样品中总酚含量降低了约5.5%。30、45和60°C热超声处理期间,黄酮醇和黄酮类化合物也观察到类似结果。热超声处理的缩合单宁含量范围为205.8至159.2 µg/g;总抗氧化能力(TAC)、DPPH和羟基自由基清除活性也显著增加。对霉菌、酵母菌和需氧中温菌进行了分析,45°C处理40分钟后均未检测到。

出于不同目的,Strieder等(48)对热超声处理的杏仁基饮料进行了植物化学分析,并确定了脂肪酸和挥发性有机化合物的组成。热超声在50°C下使用三种声功率(4.6、8.5和14.5 W)和时间(5、10和15分钟)进行。热超声处理后杏仁基饮料的pH降低,14.5 W处理的饮料观察到最低值。同样,与对照相比,处理样品中酚类化合物减少了10%。抗氧化活性结果与对照相似,至于类黄酮,14.5 W处理的样品值低于其他声功率处理的样品。测定了杏仁饮料中油酸、硬脂酸、月桂酸、棕榈酸和肉豆蔻酸的含量,声空化促进了脂肪球的减小,从而改善了样品的均质性和稳定性。50°C、14.5 W的处理可能通过美拉德反应促进非酶褐变。然而,更长时间和更高声功率的处理获得了更好的颜色效果。

### 大豆(Glycine max)

大豆是迄今为止用于饮料生产最广泛的豆类。在此方面,已进行了许多应用超声和热超声的研究。Fahmi等(47)对大豆饮料施加超声处理(35和130 kHz、20和40°C、20、40和60分钟)。他们使用反相液相色谱法测定异黄酮含量,包括染料木苷、染料木素及其相应的苷元大豆苷元和大豆苷。在两种频率下均发现异黄酮、糖苷和苷元的含量稳步增加。特别是,35 kHz处理的异黄酮含量增加比130 kHz处理更为显著。还观察到,随着超声时间(从20到60分钟)和温度(从20到60°C)的增加,异黄酮含量也相应增加。这表明温度/时间的增加与大豆饮料中异黄酮含量之间存在正相关;然而,频率具有相反的影响。综合以上结果,为了确认异黄酮的行为,有必要进一步研究超声频率、温度、时间和其他参数。

最近,Vanga等(51)研究了超声(25 kHz、400 W、1–16分钟)和微波(2450 MHz、70–100°C、2–10分钟)对大豆饮料结构、体外消化率和胰蛋白酶抑制活性的影响。随着超声处理时间的增加,胰蛋白酶抑制活性呈递增趋势。值得注意的是,16分钟时胰蛋白酶抑制剂含量的降低最为显著,达到52%。另一方面,微波的使用效果优于超声,实现了84%的降低,尤其是在100°C下处理10分钟时。消化率也有所提高,仅4分钟超声处理后即增至81.38%。随着处理时间的增加,这一趋势持续存在,最终消化率达到84.03%。分析了蛋白质结构的影响。16分钟超声处理后,蛋白质中的α-螺旋减少,β-折叠增加,表明超声可以影响大豆蛋白质的分子构象。

在此背景下,Kumar等(12)进行了微波(1、2、3、4和5分钟;900 W)和热超声(28 kHz;30、60和90分钟;40、50和60°C)。作者评估了大豆饮料中蛋白质、脂肪和总可溶性固体组成、粘度、胰蛋白酶抑制活性和脂肪氧合酶活性等不同参数。结果表明,热超声的效果优于单独超声,但微波处理的效果更好。胰蛋白酶和脂肪氧合酶抑制活性的灭活速率常数分别为0.2034和0.3232 min⁻¹。脂肪氧合酶对微波灭活的敏感性高于热超声,而相反,胰蛋白酶对热超声更敏感。通过热超声处理,蛋白质含量、脂质、总可溶性固体和粘度均增加,并受微波时间的影响。胰蛋白酶和脂肪氧合酶抑制活性的灭活速率常数分别为0.2034和0.3232 min⁻¹。这些结果表明,脂肪氧合酶对微波抑制的敏感性高于热超声。相反,胰蛋白酶对热超声更敏感。傅里叶变换红外(FTIR)分析证实了蛋白质的构象变化和分子相互作用的增强,对粘度有显著影响(热超声处理后粘度增加了高达68%)。最后,总嗜温需氧菌计数显示出显著下降。

相比之下,Park等(52)研究了紫外线(UVC)联合热超声对小球藻提取物的影响,以提供替代工艺并防止加工大豆基饮料中晚期糖基化终产物的形成。一个显著结果是大豆基饮料中大肠杆菌和鼠伤寒沙门氏菌减少了5个对数。另一方面,研究表明,巴氏灭菌后大豆基饮料中α-二羰基化合物(乙醛酸和甲基乙醛酸)和晚期糖基化终产物(Nε-(1-羧甲基)-赖氨酸和Nε-(1-羧乙基)-赖氨酸)增加。这一发现引发了关于传统巴氏灭菌方法对大豆基饮料营养质量和安全性的潜在负面影响的疑问。此外,观察到紫外线联合热超声与巴氏灭菌不同,导致α-二羰基化合物和晚期糖基化终产物减少,这可能是UVC联合热超声在维持此类饮料营养质量方面的潜在优势。同样,小球藻提取物的紫外线和热超声处理改善了抗氧化活性并保持了质量参数。

# 超声波与热超声技术处理植物基饮料的综述

## 椰子(Cocos nucifera L.)

关于超声波和热超声技术在椰子基产品中的应用研究仅有少数报道。Lu等(53)首次报道了超声波处理椰子基饮料的研究。该研究测试了一种由椰子乳液(以单硬脂酸甘油酯为乳化剂)与不同玉米添加剂(玉米粒和不同直链淀粉含量的淀粉)组成的系统,采用高强度超声波辐照处理(20 kHz)。理化性质的变化取决于玉米淀粉的类型和处理条件。超声波处理对颜色没有影响。对乳液的稳定性和结构特性进行了分析和比较。添加玉米粒的椰子饮料与添加高直链淀粉玉米淀粉的椰子饮料表现相似,但高支链淀粉含量时获得的稳定性最高。超声波处理后,发现粒径小于未经处理的饮料,且颗粒呈单峰粒径分布。另一方面,负电泳率有所改善。然而,超声波并未改变其流变行为,表现为假塑性流体。

最近,Sun等(54)研究了超声波处理(40 W/L,53 kHz)结合预热(70、80或90 °C,20 min)对椰子球蛋白和椰子饮料的理化特性和结构特征的影响。超声波结合预热(90 °C)使椰子蛋白获得了改善的乳化性能和热性能,并确认了更高的溶解度(45.2%至53.5%)、更低的游离巯基含量(33.24至28.05 µmol/g)以及更高的表面疏水性(7658.6至10815.1)。此外,FTIR和SEM显微分析显示蛋白质二级结构发生了变化。由于蛋白质理化性质的变化,zeta电位也有所增加(-11至-23 mV)。相反,观察到热聚集率降低(148.5%至13.4%),粘度增加(126.9至1103.0 mPa·s),所有结果均表明超声波结合预热可以改善热稳定性。

## 榛子(Corylus avellana)

榛子基饮料比其他植物基产品更为少见,主要原因是与该坚果相关的过敏问题。因此,关于超声波或热超声技术在榛子基饮料中应用的研究十分有限。Atalar等(43)对榛子基饮料施加了热超声处理(振幅80%和40%,处理3和5 min,温度40–45 °C)。结果表明,热超声处理样品的析水指数(%)低于传统热处理,表明其结构特性得到了改善。在流变特性方面,热超声处理使样品的平均粒径减小(约为80%振幅5分钟处理所报告值的20%)。可溶性蛋白含量也显著降低。在颜色测定方面,在特定处理条件下(40%振幅处理10 min,60%和80%振幅处理5 min),L*和b*值降低,但a*值在处理样品中没有变化。在微生物灭活方面,需氧中温菌总数以及霉菌和酵母菌分别为5.98和3.65 log CFU/mL(80%振幅处理15 min后)。在所有处理样品中还观察到酚类化合物和抗氧化活性的增加,主要与植物细胞壁破裂有关,其中60%振幅处理25 min时获得最高值。

## 玉米(Zea mays)

关于热超声技术在玉米基饮料中应用的研究仅有一篇报道。Rodriguez-Salinas等(13)研究了热超声处理(20 kHz,500 W,80%振幅,45 °C,20 min)对玉米饮料的影响,并评估了白色和紫色玉米饮料的颜色、微生物质量以及理化和营养保健品特性。结果表明,热超声处理的白色和紫色玉米饮料之间的亮度值(L*)差异较小。另一方面,热超声处理样品的a*和b*参数增加,趋向于绿色和黄色。此外,观察到需氧中温菌总数显著降低(从6.96降至4.37 log CFU/mL),肠杆菌(从5.45降至3.06 log CFU/mL),霉菌和酵母菌未检出。关于生物活性化合物,检测到抗氧化活性增加,阿魏酸和绿原酸浓度升高,但两种饮料中酚类化合物均有所减少,未检测到缩合单宁,且热超声处理的紫色玉米饮料中总黄酮含量更高。最后,白色和紫色玉米饮料的粘度根据幂律模型表现为假塑性行为。两种饮料之间的稠度系数(K)或流动指数(n)无显著差异。

## 花生(Arachis hypogaea)

与榛子和其他坚果类似,由于过敏反应的高发性,花生在饮料中的应用受到限制。因此,关于超声波在此类基质中应用的已发表研究十分有限。Salve等(55)在不同强度(200、300和400 W,处理3 min)和递增压力(0.6、0.8和1 MPa)条件下对花生饮料施加超声波处理。超声处理样品表现出比未经处理样品更高的总可溶性固形物含量、更高的蛋白质水解度和pH值。另一方面,处理样品的可滴定酸度降低。超声处理的ζ电位分析显示从-27.6 mV增加至-30 mV,表明稳定性更高。然而,400 W强度导致不稳定,ζ电位为-11 mV,并导致聚集体的形成。随着超声波强度和压力的增加,粒径减小(0.29至0.02 µm),而所有样品的行为均表现为非牛顿流体。200、300和400 W功率处理的样品表现出最佳的沉降指数,因为没有发生相分离,证明超声波强度的增加不影响产品的稳定性。样品颜色评估显示,超声波处理和未经处理的饮料之间的L*值无显著差异,除了300 W功率强度处理的样品略深于其他超声波处理样品。颜色分析显示,不同处理方法下a*值增加,b*和C*值随强度增加而降低,超声波和压力处理样品的色调值略有增加。最后,对需氧中温菌以及霉菌和酵母菌进行了微生物分析,分别减少了1.53 log和约2 log。

## 其他植物基饮料

近年来发展起来的另一个有趣类别是基于植物和乳清混合的饮料,作为乳清的再利用方式(减少其污染效应),并含有营养品质优异的蛋白质。它也适合那些不遵循100%素食饮食的人群。为此,Herrera-Ponce等(56)对乳清和燕麦(Avena sativa L.)饮料(50:50)施加超声波处理(24 kHz;0、3和10 min;23和154 W),以验证产品的品质和益处。颜色、可滴定酸度和pH值未显示显著差异。在这方面,两种超声波功率使用的近似分析(水分、脂肪、蛋白质、灰分和碳水化合物)之间未发现显著差异。然而,超声处理和热处理样品之间存在差异。超声处理样品的抗氧化能力高于巴氏杀菌样品,ABTS法结果优于DPPH法。在同一研究组发表的另一项研究中,对含有菊粉(1%和2%)的燕麦和乳清饮料进行超声波处理(23 W,24 kHz,3和15 min,10%脉冲和100%振幅),发现储存期间pH值降低,酸度增加。另一方面,大多数处理中观察到抗氧化活性增加。当评估对血管紧张素转换酶活性的抑制作用时,发现所有处理的抑制效果均超过50%,最佳处理条件为1%菊粉结合15分钟超声波处理并储存14天,抑制率为79.63%(57)。

在亚洲更常见的发酵食品基质是米基饮料。为此,Campaniello等(58)评估了超声波处理(20 kHz;130 W;40%、60%和100%振幅;2、6和10 min;2和10脉冲)对鼠伤寒沙门氏菌ATCC 35664的灭活效果。将微生物接种于米(Oryza sativa)饮料中,设置两个细胞浓度(8和5 log CFU/mL)。处理后分别获得了3和1 log CFU/mL的减少量。在4 °C下,S. enterica在13天内保持低于检测限。

大量植物基饮料已采用超声波和热超声技术开发,它们代表了一个不断增长的市场机遇。在所有情况下,所开发的产品均在实验室规模上确定,这为更大生产量提供了机遇,同时也面临着相关挑战。

## 超声波与热超声处理效应

超声波处理可通过特定作用机制增加、减少或灭活各种过程,包括热机制(热量或机械能的产生)和非热机制(空化、压缩和稀疏、自由基形成以及微机械冲击),如超声波和热超声章节中所述。因此,下文将讨论超声波和热超声对品质(理化和微生物学及酶学特性)以及稳定性(粒径、沉降和脂肪酸反应性)的影响。

### 理化性质

植物基饮料中已研究了不同的理化性质,如pH值、粒径和颜色。Maghsoudlou等(49)报道了杏仁饮料中总可溶性固形物的增加,归因于颗粒的部分烹饪或高温下水分吸收导致的颗粒膨胀。研究人员将超声处理样品中改性淀粉的减少归因于细胞壁破裂和多糖水解,包括由声学空化引起的剪切力导致的改性淀粉水解。可滴定酸度的降低是由于空化引起的颗粒电荷变化。结果,负γ电位电荷进一步增加,导致pH值升高(55)。

颜色是影响消费者感知的重要属性,也是饮料质量的视觉指标(15)。在超声波处理过程中,饮料中颗粒的散射随粒径减小而增加,导致更高的光散射和亮度值。在热超声处理的杏仁基饮料中也发现了类似结果,其中b*(黄度)和L*(亮度)等参数在40和50 °C处理温度下得到改善,悬浮液中不稳定颗粒的部分沉淀可产生有色化合物,使饮料在感官上更易被接受(11)。

### 结构修饰

超声波处理可以修饰蛋白质结构,暴露其部分内部亲水区域(59)。为此,Režek Jambrak等(60)对乳清蛋白施加超声波处理(20 kHz,43–48 W/cm²,15–30 min),发现蛋白质的分子量降低。作者还观察到蛋白质三级结构的变化,导致带电基团(NH₄⁺和COO⁻)增加,增强了蛋白质-水分相互作用。因此,超声波有助于改善饮料的保水性。另一方面,超声波通过声学空化产生的气泡内爆来减小脂肪球尺寸,产生高强度冲击波(61)。这导致均质化,使单位体积内脂肪球数量增加但尺寸减小。据报道,脂肪球尺寸的减小取决于两个因素:时间和振幅(61)。超声波处理可以增加有机或无机盐的溶解度,导致灰分含量降低(62)。

### 酶灭活

酶是一种蛋白质,其结构可受化学因素(酸度、有机溶剂、碱性等)和物理因素(辐照加热、微波等)的影响。其活性由位于酶中心的活性位点暴露程度决定。受控的构象变化可以增加酶活性,而更剧烈的处理条件可以降低酶的催化活性(66,67)。

空化、自由基形成以及超声波产生的高温高压局部条件被认为是导致酶灭活的主要机制。超声处理可破坏多肽链中的氢键和范德华相互作用,有利于酶二级结构的修饰,从而导致酶生物活性的丧失(68-70)。该技术已被证明通过加速酶反应对酶活性产生积极影响,其物理修饰方法中自由基形成和剪切力作用于酶结构并促进与底物的相互作用(71,72)。

### 生物活性化合物

酚类化合物以可溶形式存在于液泡中,或与细胞壁结合,以果胶、纤维素、半纤维素和木质素的形式存在(48)。超声波处理后酚类含量的增加可归因于细胞壁的破坏,这可能促进结合酚类的释放(63)。热超声处理对生物活性化合物的增加可能是由于次级代谢物的释放,因为空化增强了细胞壁的机械破裂(11)。Ghasemzadeh等(64)报道声波破坏生物细胞并促进细胞内容物的释放。然而,较高的热超声温度可能由于热降解而降低这些化合物的含量。此外,热超声提供的声能可导致抗氧化能力的增加和下降,以及有利于超声处理介质中生物活性化合物的生物利用度,并促进羟基自由基的产生,当使用高温和高功率时,气泡破裂同样可氧化酚类化合物(17)。

高温热超声处理过程中生物活性化合物的减少可能与处理参数有关,包括处理时间、温度和功率(65)。另一方面,自由基形成的减少与抗氧化活性的增加有关,但长时间大量的自由基可抑制抗氧化活性(65)。同样,据报道,较长的超声波处理时间和温度下自由基清除活性较低,而较短时间和温度下则较高(11)。

### 沉降指数、粒径和流变特性

沉降是指颗粒或大分子在惯性场中的运动。沉降机制可以用斯托克斯定律解释,其中沉降颗粒的速度和密度与分散介质相互作用(43)。在这种情况下,可能发生不同类型的行为。一种情况是,颗粒与连续相之间密度不同的大颗粒沉降加速。另一方面,密度高于连续相的颗粒将在重力作用下沉降。在牛奶等液体食品中,过度沉降会成为品质问题(73)。

由于空化效应,热超声处理通过释放增加平均粘度的胞内化合物来降低沉降速率(43)。在超声波处理的花生基饮料中(20 kHz,200、300和400 W),未观察到相分离,表明超声波强度的增加不影响颗粒的稳定性,沉降指数值证明了这一点,基于颗粒尺寸的减小从而促进了分子间反应。此外,它可引起花生蛋白变性,通过暴露活性位点促进花生蛋白分子的展开,并增加分子表面的疏水性(55)。

另一方面,粒径受到影响,因为超声波通过低频声学空化分解植物和饮料颗粒(43)。微气泡在界面附近不断坍塌,产生局部湍流。声波、微流产生的高剪切力和高压冲击可导致较大液滴的破碎(53)。

流变学是食品表征的基本组成部分,定义为研究物质变形参数的科学,这些参数根据食品加工到最终产品的制造过程而变化(74)。Maghsoudlou等(49)在杏仁基饮料中使用超声波,发现流动指数(n)降低而稠度系数(K)增加;这可能与超声处理下膨胀淀粉的收缩以及由解聚、碳水化合物或热凝固引起的网络破坏有关(54)。然而,热超声处理不影响粘度,但可能通过帮助分布和减小水胶体尺寸来改善粘度(13)。

### 微生物灭活

多种机制解释了热超声处理对微生物的灭活效应,包括空化现象,它能够通过形成孔隙(声穿孔)损害微生物的细胞壁和膜。声穿孔也称为细胞超声处理,它产生气泡并引起声学空化,从而改变细胞质膜的通透性(15)。这导致细胞破裂,从而造成胞内物质损失(14)。超声波穿孔微生物的细胞膜,胞内基质的挤出产生自由基,最终杀死微生物(75)。空化还有助于通过灭活线粒体的酶活性来抑制微生物生长(76)。形态学,如微生物的类型、形状或直径,影响微生物灭活的效率,使热超声处理对不同微生物的效果不同。在这方面,革兰氏阴性菌的抵抗力低于革兰氏阳性菌。由于其肽聚糖包被,细菌孢子和霉菌比营养体细菌对超声波更具抵抗力(76)。

### 脂肪酸

用于植物基饮料的谷物(如燕麦)、豆类(如大豆)、核桃、榛子和杏仁以及某些种子(如向日葵或芝麻)富含饱和和多不饱和脂肪酸,其中一些由超过90%的多不饱和脂肪酸组成(39)。热超声处理引起的脂质氧化可能是由于热降解和声化学降解。热超声处理过程中产生的高温和产生的自由基可能促进脂质的氧化。然而,尽管空化产生的微气泡可促进脂质氧化,但短的保留时间和减少的热暴露可防止热超声处理过程中氧化化合物的形成。另一方面,声学空化通过促进脂肪球的减小,使含脂样品具有更好的均质化和稳定性(48)。值得注意的是,热超声处理的榛子饮料未促进氢过氧化物的形成,尽管它显示了脂肪酸的降解(48)。

基于所获得的微生物学和理化结果,超声波应用已被证明适用于食品加工,因为它提供了将颗粒减小与微生物灭活结合在一台设备中的可能性,这可以为食品加工商带来时间和成本的重要降低。

## 挑战与未来工作

当今消费者正在推动食品工业开发一系列创新产品,这些产品不仅提供感官和营养特性,还具有功能性和可负担性。因此,饮料市场的未来将取决于提供健康生活方式选择,并考虑食物过敏和不耐受的普遍性。在这方面,植物基饮料的挑战不仅在于植物基质和提取过程,还在于在保持化合物品质和生物功能性的同时用于保存它们的技术。在这方面,超声波和热超声处理已被证明为植物基饮料提供了若干优势。此外,这些技术可作为这些植物基饮料的预发酵工艺,从而生产出高产且优质的发酵产品(57,76)。

此外,工艺放大是超声波和热超声处理应用及其成功进入市场可能面临的最大挑战,设备设计师需要进行重大改进以增加处理量。然而,该行业仍在利基生产环境中运营。同一研究方向还可包括与其他技术(如紫外线、微波和过滤等)的可能组合。最后,食品工业正试图采用环保技术,如热超声处理,这些技术通过减少能源和水消耗在加工中具有可持续性。

## 结论

社会对非乳制品日益增长的需求以及食品行业日益激烈的竞争,强调了超声波和热超声处理等前沿技术作为传统植物基饮料加工方法合适替代方案的潜力。这些技术不仅提高了这些饮料的品质,还能够生产清洁标签产品。尽管目前尚无能够处理大体积的超声波设备,但设计表明这一障碍在不久的将来可能被突破。此外,由于它们具有可持续性,符合环境标准,并为促进生态和工业目标的未来商业应用打开了大门。