Ann. Anim. Sci., Vol. 24, No. 4 (2024) 1037–1049 DOI: 10.2478/aoas-2024-0020
Influence of various methods of processing soybeans on protein digestibility and reduction of nitrogen deposits in the natural environment – a review*
Muhammad Umair Asghar♦, Qurat Ul Ain Sajid, Martyna Wilk, Damian Konkol, Mariusz Korczyński Department of Animal Nutrition and Feed Sciences, Wrocław University of Environmental and Life Sciences, Norwida 25, 51-630 Wrocław, Poland ♦ Corresponding author: muhammad.asghar@upwr.edu.pl Abstract Soybean meal (SBM) is a significant source of protein for poultry due to its high concentration of protein and amino acids profile. The primary objective of SBM processing is the reduction and deactivation of anti-nutritional factors (ANFs) to enhance nutrient digestibility. However, eliminating ANFs does not necessarily correlate with increased protein and amino acid content. Several processing methods, such as soaking, cooking, and commercial techniques, improve SBM protein digestibility. To sustain feeding qualities, soybeans must undergo heating to remove inherent chemicals that interfere with poultry digestion. However, both under and over-processing can impair meal digestibility. Extrusion heating significantly contributes to protein and starch digestibility while reducing certain ANFs. Thermomechanical and enzyme-assisted procedures reduce heat-resistant proteins more efficiently than extraction methods, producing soy protein concentrate (SPC) and fermentation. These techniques reduce ANFs in SBM, activating digestive enzymes and alleviating digestive tract pressure, leading to decreased endogenous protein deficits. Exogenous enzyme supplementation is a biotechnological approach for enhancing the nutritional content of SBM and certain other protein-rich products. However, different processing methods not only affect protein digestibility but also impact poultry production, gastrointestinal health, and the environment due to higher nitrogen excrement. Ammonia (NH3) emissions are a significant environmental concern in chicken farming, resulting from uric acid production during protein consumption. It has a negative impact on the environment and the health of birds/humans. This review investigates the impact of several processing techniques on the digestibility of SBM protein and the reduction of N2 regarding one health concept. Future research should focus on identifying optimal processing methods maximizing protein digestibility while minimizing environmental nitrogen impacts. Key words: nitrogen emission, one health, protein digestibility, soybean processing methods
Soybean (Glycine max (L.) Merrill) is a leguminous plant grown primarily for its high protein (40%) and fat (20%) content (de Visser et al., 2014). It is commonly used in the feed industry as a protein-rich, defatted, and toasted SBM for livestock (Stein et al., 2008). The rising demand for imported soybean is ascribed to its substantial crude protein (CP) level and amino acid (AA) composition, which is supplementary to cereals, as well as its high AA bioavailability (de Visser et al., 2014; Ravindran et al., 2014). In the European Union (EU), most of the SBM is imported from genetically modified cultivars, and accounts for 80% of plant protein-rich feed materials, and 95% of that was used as livestock feed (Guo et al., 2022; Lannuzel et al., 2022). Soybean agriculture accounts for about 2% of farmlands in the EU, even though this percentage is predicted to rise (EU agricultural outlook for markets, income and environment, 2021–2031) (FAO, 2023).
Genetically modified (GM) soybeans have been subjected to criticism and concerns mostly related to environmental, health, and socio-economic factors. Firstly, a significant concern arises over the environmental consequences associated with the utilization of herbicides, glyphosate (which has been accused of the spread of cancer in humans), which can result in the emergence of herbicide-resistant weeds and pose a possible threat to biodiversity. Secondly, the phenomenon of gene flow, in which genetically engineered features might disseminate to non-genetically modified crops, gives rise to ecological uncertainties. Thirdly, the health issues associated with GM soybeans mostly pertain to the possible presence of allergens, changes in nutritional composition, and the existence of antibiotic resistance indicators. The consolidation of GM seed production among a small number of biotechnology corporations presents difficulties in maintaining the agricultural variety and farmer independence.
____________ *The APC/BPC is financed/co-financed by Wrocław University of Environmental and Life Sciences. 1038 M.U. Asghar et al.
The aforementioned shared concerns highlight the necessity of acquiring a comprehensive comprehension of the possible hazards linked to GM soybeans, with a focus on the significance of responsible and sustainable agriculture methods (de Visser et al., 2014; Sieradzki et al., 2021). European governments have pushed an expansion of local cultivation of non-genetically modified (nonGM) soybeans and other protein-delivering legumes. This progressive approach aims to reduce their reliance on imported protein supplements and mitigate environmental difficulties associated with imported GM soybeans (Martin, 2015; Balázs et al., 2021). In addition to increasing soy farming, a suitable processing framework should be built, as big, optimized processing factories are currently positioned distant from all growing locations. Local small-scale processing may have the ability to increase farmers’ protein self-sufficiency. It is generally understood that optimal soybean processing is critical for delivering adequate feeding value. Soybeans have emerged as a well-established staple crop in Austria, followed by maize, wheat, and barley (Carr et al., 2020). In Poland, imported GM soybean meal covered 65%, while locally cultivated leguminous seeds covered 11% of protein requirements for livestock nutrition (Niwińska et al., 2020; Dzwonkowski et al., 2021). Because of its nutritive value, high concentration of crude protein (44– 48.5%), and stable amino acid profile, this plant is a suitable protein source for poultry (Dale, 1994). Over half of the soybean meal (SBM) produced in the USA is fed to broiler chickens (Loeffler et al., 2013). Feed makes up 60–70% of the costs of poultry production, with energy being the most expensive component in the feed (Flachowsky and Meyer, 2015; Ahiwe et al., 2018; Noblet et al., 2022). In order to acquire maximum benefits from poultry production (eggs and meat), formulating a diet tailored to meet the nutritional demands of the birds is essential, contributing to the overall economy (Asghar et al., 2021; Sierżant et al., 2023). The purpose of this updated review is to offer a comprehensive analysis of the changing patterns in the processing of SBM, with a focus on its historical development and recent progress. This improved narrative will provide a more in-depth examination of how these patterns have significantly influenced the enhancement of nutritional value, in terms of protein digestibility and the reduction of ANFs. Producing highly digestible feed also helps to reduce environmental pollution caused by excessive nitrogen outflows. Another strategy for minimizing ammonia emissions from poultry farming is reducing feed protein and supplementing it with indispensable amino acids. These approaches have the potential to lead to positive long-term changes, promoting environmental safety, animal welfare, and human health. This review evaluates the impact of different processing techniques on SBM protein digestibility and the reduction of nitrogen excrements for poultry production and environmental sustainability.
Material and methods A systematic review of peer-reviewed articles published in PubMed (www.ncbi.nlm.nih.gov; last accessed on August 2023); ISI Web of Science (www.webofknowledge.com; last accessed on August 2023), Google Scholar (scholar.google.com; last accessed on August 2023), and ScienceDirect (www.sciencedirect.com; last accessed on August 2023) databases was performed covering last 30 years, including older, primary, and original references. More than 60% of the references were from the past 10 years. Studies were selected if they reported different soybean processing methods to remove ANFs and their impact on protein digestibility. A total of 120 studies from 76 different journals and books, and other scientific reports met the specific standards and were included in the present review. The review is divided into the following sections: a description of various ANFs present in soybeans, methods to remove ANFs from soybeans, and their future perspectives in poultry nutrition. Anti-nutritional factors (ANF) in soybean The quality of SBM is ascertained by its amino acids concentrations and the presence of chemical components, known as anti-nutritional factors (ANFs). Unprocessed SBM contains ANFs that possess the potential to significantly reduce its nutritional value, resulting in decreased animal health and productivity (Fekadu Gemede, 2014; Rocha et al., 2014). ANFs have a detrimental effect on feed consumption and nutrient digestibility of SBM, which is widely regarded as the primary protein supplement in broiler diets across the world (de Coca-Sinova et al., 2008). These ANFs can negatively impact the digestion of energy, amino acids, and other nutrients, resulting in reduced animal performance, including poultry. Soybeans must be treated to remove these ANFs, which is especially important in the case of monogastric diets. Numerous protease inhibitors known as trypsin inhibitors (Rada et al., 2017), hemagglutinins or lectins (Ebere, 2016; Udeogu and Awuchi, 2016), goitrogens (Barros Dourado et al., 2011; Bajaj et al., 2016), saponins (Omizu et al., 2011; Chaturvedi et al., 2012), and urease are among the harmful components in soybeans (Khan et al., 2013; Real-Guerra et al., 2013). The prevalence of these components in relatively high concentrations limits the use of soybeans and their derivatives in monogastric diets. Those anti-nutritional substances are the main determinants forcing proper processing of soybeans. ANFs, such as trypsin inhibitors, in raw soybeans exert deleterious effects in birds disturbing the digestion process in the gastrointestinal system. Moreover, the nutritional benefit of SBM for poultry is restricted by a number of ANFs that conflict with feed consumption and nutrient utilization. A high concentration of protease inhibitors, particularly trypsin inhibitors (TI), reduces protein digestibility and AA bioavailability. The TI’s deleterious effects on monogastric animals are widely documented in the literature (Ravindran et al., 2014, 2017; Dzwonkowski et al., 2021). TI
have been shown to interact with protein metabolism in the gastrointestinal system of young chickens (Goebel and Stein, 2011), and uncooked soybean meal induces pancreas expansion in growing chickens due to the presence of destructive elements in substantial quantities (Dei, 2011; Erdaw and Beyene, 2018; Beukovic et al., 2012; Foley et al., 2013). Furthermore, excessive levels of protease inhibitors (PI) in the diet produce pancreatic hypertrophy/ hyperplasia, resulting in poor growth parameters (Jahanian and Rasouli, 2016; Gilani et al., 2012). Pancreatic enlargement is caused by pancreatic secretory stimulation when the pancreas adjusts for the increased number of blockers in the intestinal system. The impacts of raw SBM on chicken development suppression could not be addressed by enriching the diet with methionine, lysine, and so forth (Loeffler et al., 2013). Methods to remove ANFs in soybean The soybean is a widely used protein source in poultry feed due to its high protein content but it contains certain ANFs that limit its nutritional value. However, the protein in soybeans is not easily digestible by poultry, which can lead to reduced growth and feed efficiency. To counteract this, various processing methods, including heat treatment, fermentation, enzyme treatment, and chemical treatment methods have been developed to effectively reduce or eliminate ANFs present in soybeans, as shown in Figure 1. By exploring these strategies, we aim to shed light on how they contribute to enhancing the digestibility and nutritional value of soybeans, thus mitigating their adverse effects on poultry performance.
Heat treatment (HT), including roasting or boiling, has been demonstrated to effectively reduce levels of TI and lectins in soybeans (Kumar et al., 2022). This method contributes to enhancing the nutritional profile of soybeans, promoting better digestibility and utilization. Fermentation, used in the production of traditional soy products like soy sauce and miso, has been shown to reduce ANF levels and improve the digestibility of soybeans (Lu et al., 2022). Enzyme treatment, including protease and phytase supplementation, effectively reduce ANF levels and improves the nutritional value of soy products (Samtiya et al., 2021). Another effective method for eliminating ANFs from soybeans is the chemical treatment approach. It has been reported that most of the plant protein contains intramolecular disulfides, if this concentration of disulfide can be decreased then the deleterious effect of ANFs can also be controlled. This strategic approach aims to enhance the overall quality of plant proteins (Xiong and Guo, 2021). Heat processing to remove ANFs in soybean Heat processing, including cooking, roasting, toasting, and extrusion, is one of the most common methods used to improve soybean protein digestibility. This method denatures the proteins and reduces the activity of ANFs, such as TI, lectins, and protease inhibitors (Figure 2). In addition, heat processing enhances the availability of essential amino acids, making the protein more easily digestible for birds. Several studies which show the effect of heat processing methods on soybean digestibility are presented in Table 1.
Figure 1. Schematic representation of various processing methods of soybean with respect to protein digestibility and their effect on the environment (own elaboration) 1040 M.U. Asghar et al.
Figure 2. Schematic representation of heat processing methods on soybean and their effect on protein digestibility in poultry (own elaboration) Table 1. Effect of heat processing method on digestibility of soybean protein and on ANF