2023 Volume 29 Issue 4 Pages 277-288
Soybean, a staple crop, is a source of high-quality protein and, thus, has broad prospects in the food industry and other fields. This review first introduces common soybean protein products and then elaborates on the safety and biological activity of soybean protein. In addition, excellent processing characteristics are introduced and an example of the comprehensive utilization of soy protein is given. Soybean peptides are an essential extension product in the soybean processing chain. Hence, this paper also introduces soybean peptides' biological activity. Moreover, traditional, and novel techniques for processing soybean protein isolate and peptides are compared in terms of their advantages and characteristics, and new ideas are proposed for their green production on an industrial scale. It is hoped that the analysis and innovative concepts proposed in this work will promote the healthy development of the soybean protein industry chain.
Plant proteins are comparatively more sustainable than animal proteins in terms of their impacts on fossil fuel, land use, and water consumption (González et al., 2011). With the human population projected to increase to 9 500 million by 2050 (Reynolds et al., 2015), plant sources are becoming increasingly essential to provide most of the nutrients needed for human sustenance. Soybean is one of the first generations of plant-based protein sources consumed by humans. Native to China, the crop has been cultivated in various regions for more than 5 000 years and is a staple protein in the traditional diet. Records of soybean porridge date from as early as 240 BC, with the preparation of tofu, fermented bean curd, and tofu skin developing gradually over the next two thousand years (Shurtleff and Aoyagi, 2014; Mah et al., 2019; Gbejewoh et al., 2022). Soybean has been grown in the United States and Brazil since the late 1800s, with production increasing rapidly since the 1970s and, together, the two countries now dominate global soy productioni). Soybean protein foods have also gained popularity in Europe and other parts of the world and are consumed in a variety of forms, such as tofu, soybean yogurt, natto, and many others (Singh and Krishnaswamy, 2022).
Soybeans are rich in various biologically active ingredients, among which protein is the main active component (Cabanos et al., 2021). It contains all the essential amino acids required by the human body and, thus, can provide an excellently balanced vegetable protein intake (Ali et al., 2010). While soybeans are somewhat limited in application due to the complexity of their composition, their anti-nutritional factors can be removed during processing to obtain soybean protein isolate (SPI), which safely retains the nutritious characteristics (Shi et al., 2018; Pi et al., 2021). The biological activity of SPI has been extensively studied and shown to include cardiovascular disease risk reduction via the lowering of cholesterol, immunity improvement, osteoporosis relief, and the improvement of intestinal flora balance (Rist et al., 2012; Bedani et al., 2015; Zhang et al., 2018; Qin et al., 2022). SPI also has excellent processing characteristics, which make it applicable for gelling, emulsifying, texturing, and enzymatic processing (Deng, 2021; Lv et al., 2021; Huang et al., 2022b). Thus, soybean protein is a subject of overall development and application prospects in medicine, health care, novel food, and other fields (Singh and Krishnaswamy, 2022).
This paper expounds on soybean products, their production processes, edible safety, the nutritional effects of soybean protein and peptides, and the main processing characteristics of soybean protein. In addition, the review compares the differences between traditional and new processing technologies and asserts the advantages and characteristics of the new technology. Thus, this work provides a comprehensive theoretical reference for the efficient production and high-value utilization of soybean protein and related products.
Soybean protein products Soybeans are rich in nutrients, with an abundance of protein (35–45 %), lipid (15–25 %), carbohydrates (30–35 %), dietary fiber (17 %), and traces of micronutrient (Singh and Krishnaswamy, 2022; Sucheta et al., 2014). In production, the first step is to separate the oils and isolate the soybean protein for subsequent use, which is most done through low-temperature leaching. In addition, defatted soybean meal is produced by removing fatty acids and oils from soybean meal with the help of solvents. After the oils are extracted by leaching, the solvent is removed from the soybean meal under low-temperature conditions, and the soybean protein is undenatured. The defatted soybean meal can then be further processed into protein products such as soybean protein powder, soybean protein concentrate (SPC), and SPI. SPC is obtained from defatted soybean meal through alcohol extraction, flash evaporation, and vacuum deodorization. After processing, a large amount of low-molecular-weight and soluble non-protein components are removed until the crude protein content on a dry basis range from approximately 65 % to 90 %. SPI is currently the most utilized soybean protein product in the food industry since it offers various excellent processing characteristics. Traditionally, the processing is performed by weak alkali extraction and acid precipitation, in which the protein nears the isoelectric point at a pH of approximately 4.5, where precipitates are formed, and the precipitated protein is obtained after separation. However, since SPI is hydrophobic, the protein carries pigments, polar lipids, and other substances that settle together, resulting in a dark color and distinctive beany smell, affecting SPI's application in foods. Furthermore, this traditional method produces at least 24 tons of wastewater for every ton of SPI, resulting in severe environmental pollution. Therefore, the Chinese government severely restricts the development of the soybean protein deep processing industry.
New SPI production technology The production of SPI with no beany smell, good color, and which requires significantly less wastewater to be discharged during processing is an urgent technological challenge for the soybean protein industry. Liu et al. (2003) invented a new method of SPI production which extracts the protein directly after the pretreatment of defatted soybean meal. A hierarchical extraction strategy was constructed for soybean protein processing. In this invention, a multi-step alcohol process was used to extract various components with different physicochemical properties, and non-protein components such as lipids, pigments, and soluble oligosaccharides were separated. This innovation avoids the influence of hydrophobicity and the adsorption of pigments, polar lipids, and other substances on the protein surface during acid precipitation. Consequently, the SPI obtained by this novel process has almost no beany flavor. Its color tends to be milky white (Fig. 1A). Moreover, the amount of water required for this innovative process is half that needed for the traditional weak alkali extraction and acid precipitation process. At the same time, the wastewater discharged to produce one ton of SPI is only approximately one ton, which is one-twentieth that of the traditional process.
(A) SPI production process and comparison of traditional and new production technology (B) Comprehensive utilization of SPI in “Soybean protein-based meat”.
These characteristics of this innovative SPI processing provide excellent support for further expanding the application field of SPI and improving the quality of soybean protein products. Based on this, the laboratory has also done a lot of research on physiological functions, processing characteristics, and product applications (Li et al., 2020; Zhang et al., 2021a; Chen et al., 2022; Huang et al., 2022b). The novel production process has matured and is being implemented and promoted in China.
Anti-nutritional factors in soybean The anti-nutritional factors in soybean, such as trypsin inhibitors and lectins, can affect the absorption, utilization, and metabolism of its nutrients and even cause a series of adverse reactions, thus limiting its application potential (Gu et al., 2010; Vagadia et al., 2017; Wen et al., 2021; Padalkar et al., 2023). Trypsin inhibitors, among which Kunitz trypsin inhibitor (KTI) and the Bowman-Birk inhibitor (BBI) have the most serious effects, are present mainly in the cotyledons of soybean seeds. KTI mainly inhibits trypsin and has a weak inhibitory effect on chymotrypsin, while BBI has a strong inhibitory effect on both trypsin and chymotrypsin (Vagadia et al., 2017; Padalkar et al., 2023). It is generally believed that trypsin and chymotrypsin react rapidly in the small intestine, binding to trypsin inhibitors and rendering them inactive. This action reduces protein digestibility, resulting in the loss of absorbable nitrogen. In turn, this causes excessive secretion of trypsin and chymotrypsin through a feedback mechanism, which leads to the loss of endogenous nitrogen and sulfur-containing amino acids, thus hindering the growth and development of animals (Qiao, 2016).
Soybean lectin, a glycoprotein constituting approximately 3 % of the soybean, is a tetramer composed of four subunits. Lectins cannot be hydrolyzed by proteases in the digestive tract of animals and have a high affinity for sugar molecules. Moreover, they have been shown to bind to specific receptors on the surface of epithelial cells in the small intestine wall, thereby destroying its brush-like mucosal structure and interfering with the function of the mucosa to secrete various enzymes (Pusztai et al., 1990; Fasina et al., 2003). The ability of the digestive tract to digest and absorb nutrients was found to be significantly reduced in this process, thereby decreasing the protein utilization rate of the animal body, and significantly hindering growth development (Wen et al., 2021). However, the main anti-nutritional factors in soybean, such as protease inhibitors and lectins, are heat labile and, therefore, flash evaporation at a temperature of more than 120°C can effectively inactivate them during SPI processing to improve edible safety (Shi et al., 2018; Pi et al., 2021). In addition, urease, another critical anti-nutritional factor in soybean, generally has no toxic effect. However, under appropriate temperature and pH conditions, it quickly decomposes nitrogenous compounds into ammonia when it encounters water, thereby causing ammonia poisoning (Gandhi et al., 1984). Thus, urease activity is commonly used to assess the degree of soybean heat exposure and to evaluate trypsin inhibitor activity. Its thermal instability is generally utilized in processing, and it can be inactivated by appropriate heat treatment, thereby eliminating its potential hazard (Pi et al., 2021).
Allergenicity of soybean protein Some studies have found that soybean protein may have a degree of allergenicity, especially for specific populations (Sung et al., 2014). One investigation into the clinical response of children with symptoms of soybean protein allergy used diagnostic tests, such as the radioactive allergy adsorption test (RAST), skin prick test (SPT), and a double-blind placebo-controlled and food-controlled trial (DBPCFC) and found that of the 317 children with an allergic constitution, the positive rate of RAST was 22 % while only 3 % of DBPCFC tested positive (Giampietro et al., 1992). In a study of 163 patients with protein allergies, children taking soybean protein isolate showed a positive SPT rate of 13 %. In contrast, egg, peanut, and milk showed positive SPT rates were 35 %, 34 % and 19 %, respectively, and a positive DBPCFC rate of 1.8 % (Burks et al., 1998). These data show that children with protein allergies tend to have low soybean protein isolate allergy rates. Other studies have shown that infants with milk protein allergies may also develop soybean protein allergies when soybean protein is substituted for milk-based infant formula but at a far lower rate. Beck and Atkins (1990) reported that only 7 % of 54 infants allergic to the milk-based formula developed soybean protein allergy (Bock and Atkins, 1990), while Klemola et al. (2002) reported that eight out of 80 infants with milk allergy (10 %) developed an allergy to soybean-based infant formula in their study (Klemola et al., 2002). Therefore, soybean protein can be used as a substitute for milk protein allergy patients to reduce their allergic risk.
The United States Food and Drug Administration (FDA) has approved the food safety of SPI, including it in the organization's ‘generally recognized as safe’ (GRAS) list, which further reports a 24-week study of six men with metabolic problems who experienced no adverse reaction to SPI consumption. Furthermore, a scientific report on soybean protein edited by Yang et al. (Yang and Li, 2011), entitled “Application Guidelines for Nutritional Functional Components,” found that there was no clear population group for which soybean protein is unsuitable. Their research on the safety of soybean protein also showed no reports of acute toxicity, genotoxicity, chronic toxicity, carcinogenicity, or reproduction and development toxicity in the relevant literature. In contrast, sub-chronic toxicity showed oral soybean protein 60 g/d for 16 weeks without side effects (Yang and Li, 2011). Thus, soybean protein is currently considered a relatively safe substitute protein source for the human body.
Hypolipidemic effect Considerable attention has been paid recently to the associated health benefits of soybean protein. Particularly, it can reduce the risk of cardiovascular disease (CVD) by lowering the blood's low-density lipoprotein (LDL) levels. Moreover, many animal and human experiments have demonstrated the reduction of serum cholesterol levels through the ingestion of soybean protein (Bedani et al., 2015). Beresneva and Parastaeva (2019) measured the echocardiographic changes in Wistar rats fed with either a high-salt diet or a high-salt diet supplemented with soybean protein. High salt intake can cause cardiac remodeling, but it was found that soybean protein could counteract this process. After a 12-week experimental period, the soybean protein-fed groups had significantly lower plasma total cholesterol, triglycerides, and LDL-cholesterol concentrations compared with the control group in rats fed a cholesterol-rich diet (Yang et al., 2007). In another study, Blanco Mejia et al. (2019) analyzed 46 studies that compared the LDL in the blood of a non-soybean protein control group with that of volunteers fed with soybean protein at a dose of 25 g/d for six weeks. Continuous soy feeding reduced LDL and cholesterol levels by approximately 3 to 4 %. In other research, 33 randomized controlled trials on the relationship between soybean protein and cholesterol since 1995 were analyzed (Sirtori et al., 2007). The results confirmed that soybean protein could effectively reduce cholesterol levels and that this effect is related to the initial cholesterol content in the body. Many studies have shown that the bioactive peptides in soybean protein exert cholesterol-lowering bioactivity (de Lima et al.; Liu et al., 2022).
Improved immunity Soybean protein has also been shown to improve immune function significantly and to inhibit the inflammatory response to a certain extent (Minehira et al., 2000; Zhang et al., 2018), such as the inhibition of inflammatory marker tumor necrosis factor-a in spleen tissue (Kuda et al., 2012). Glycinin helped to increase intestinal mast cells and histamine release in 18-day-old weaned piglets (Sun et al., 2008). Soybean protein significantly increased the serum levels of immunoglobulin (Ig) M, IgG, and IgA and significantly reduced the contents of macrophage inflammatory protein-2 (MIP-2) and regulated upon activation normal T cell expressed and secreted (RANTES), decreased the contents of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), and in a study on immune modulation and inflammatory inhibition of soybean protein on Staphylococcus aureus-induced epidermal trauma in aged mice with negative nitrogen balance. (Zhang et al., 2018). The ingestion of soy meal has been reported to alter the expression of immune genes in Atlantic halibut (Murray et al., 2010). Proven benefits such as these, which show improved immunity and healthcare, have led to growth in the market for functional soybean protein.
Soybean protein and probiotics Probiotics are a class of active microorganisms that can improve the host's micro-ecological environment and benefit the host's health when sufficiently colonized in the body's intestinal tract or reproductive system (Mesquita et al., 2017). The primary growth substrate for gut microbes is food that is not absorbed in the upper digestive tract, which may include indigestion oligosaccharides, dietary fiber, and proteins (Fooks et al., 1999). Among them, proteins with potential prebiotic effects have recently been of particular interest to researchers. Studies have shown that soybean protein isolates and their digests can promote the growth and short-chain fatty acid production of Lactobacillus rhamnosus under mono-culture and co-culture conditions (Zhang et al., 2021a). Butteiger et al. (2015) compared the effects of soybean protein and milk protein on the intestinal flora of hamsters by feeding them either milk protein isolate, SPC, partially hydrolyzed SPI, or soybean protein isolate for six weeks. It was found that the microbial diversity in each soybean protein-fed group was higher than that of the milk protein-fed group. Soybean protein can alter the intestinal environment, affecting fermentation by the intestinal microbiota and the generation of putrefactive compounds. (An et al., 2014). The addition of casein or soybean meal at 30 g/kg body weight and 60 g/kg body weight, respectively, to the feed of weaned piglets was shown to promote the proliferation of intestinal probiotics, and the results were more significant with higher soybean addition levels. Adequate feed intake promotes the proliferation of beneficial bacteria, thereby contributing to improved intestinal flora (Rist et al., 2012).
Soybean protein improves osteoporosis Osteoporosis is prone to occur in postmenopausal women, in which reduced estrogen alters the bone mineral composition, resulting in the loss of mineralized bone tissue and structural failure (Zheng et al., 2016). Research, ovariectomized animals were used as a model of menopause to investigate the effect of soy protein intake on bone resorption and bone formation in postmenopausal women. It has been shown that the consumption of soybean protein can have modest beneficial effects on bones (Rizzo and Baroni, 2018; Qin et al., 2022). In one experiment, the biomechanical properties of bones in female rats were improved following soybean protein intake, regardless of their ovarian hormonal status (Hinton et al., 2018). However, population experiments on postmenopausal women had shown that soybean protein with isoflavones might confer a beneficial effect on bone health, when soybean protein alone had no significant effect (Sathyapalan et al., 2017). In addition, soy isoflavones may prevent bone loss by increasing bone mineral density in normal-weight individuals and reducing bone resorption in overweight individuals (Akhlaghi et al., 2020). However, while soybean protein can improve and prevent osteoporosis caused by aging in postmenopausal women, the intake of soybean protein may be accompanied by an increase in the levels of other hormones, and the related mechanism of action is still unclear and requires more in-depth research. That said, soybean protein holds great promise in improving osteoporosis, and its use in combination with other nutrients is one of the ways to improve osteoporosis.
Biological activity of soybean peptides Soybean peptides, the small molecular products of soybean protein hydrolysis, have provided multiple health benefits (Chatterjee et al., 2018; Kim et al., 2021). In addition to improving immunity (Kim et al., 2021; Yimit et al., 2012), regulating intestinal flora (Zhang et al., 2021b) and lowering cholesterol (Liyanage et al., 2009), soybean peptides can also influence electron transferring ability of the amino acid residue and the upregulation of cellular resistance oxidase activity (Amakye et al., 2021). In one study, following soybean peptide treatment, the gene expression levels that stimulate antioxidant enzymes and nuclear factor erythroid-2-related factor 2 (Nrf2) signaling pathways were increased (Yi et al., 2020). Two cholesterol-lowering peptides derived from glycinin were shown to inhibit 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMGR) activity in cultured Hepatocellular carcinoma (HepG2) cells and promote LDL uptake by the LDL receptor sterol response element binding protein 2 (LDLR-SREBP2) pathway which control of cholesterol biosynthesis gene expression (Pak et al., 2005a, 2005b). Soybean peptides could significantly promote cell proliferation. Additionally, soybean peptides could alleviate LPS-induced inflammation by reducing the production and expression of nitric oxide (NO), TNF-α, IL-1β, and IL-6. Moreover, soybean peptides could promote the mRNA expression of proteins related to inflammation inhibition (IL-10) and tight junction modulation (Wen et al., 2022). These findings provide a theoretical basis for soybean peptides to be used as nutritional supplements to relieve exercise-induced fatigue.
Soybean peptides can also inhibit the production of reactive oxygen species (ROS) induced by hydrogen peroxide, malondialdehyde, and oxidized glutathione in liver cancer cells (Yi et al., 2020). Soybean peptides have also been shown to have hepatoprotective effects. Selenium-enriched soybean peptides can reduce the apoptosis rate induced by carbon tetrachloride and alleviate liver fibrosis through various pathways, which could be considered a potential therapeutic drug for treating liver fibrosis (Liu et al., 2019). In examining the protective effect of soybean peptide on the liver, Chen et al. (2022) found that it significantly prevents the liver from heat stress and exercise fatigue-induced injury and asserted that this might be related to its antioxidant effects. This result can be explained by increasing glutathione (GSH) and GSH peroxidase (GSH-Px) in the liver and protect the liver by regulating the NF-κB/I κB pathway. In addition, soybean peptides have been shown to be effective in modulating cellular immune systems, regulating neurotransmitters, and boosting brain function (Yimit et al., 2012). These findings confirm soybean peptides' broad application potential and huge market value as an easily digestible and fast-absorbing protein nutrient source.
Processing technology of soybean peptides In the production and processing of peptides, the difficulty is obtaining high-yield peptide products and ensuring potent bioactivity (Udenigwe and Aluko, 2012). Post-consumption absorption efficiency is essential to provide the human body with the expected benefits of amino acid nutrition. In the traditional process, several enzymes are mixed with soy protein for hydrolysis and separation (Sun, 2011; Feng et al., 2022). The molecular weight of the peptides varies widely, and some proteins have not been hydrolyzed (Fig. 2A) (FitzGerald and O'Cuinn, 2006). The recent introduction of multi-enzyme step-by-step directional enzymatic hydrolysis technology effectively addressed these challenges, breaking through the technical bottleneck of low enzymatic hydrolysis efficiency and the large randomness of enzyme cutting sites. This technology significantly improved the degree and yield of enzymatic hydrolysis (Fig. 2B). At the same time, continuous concentration and separation technology can realize continuous production while overcoming the problems of high energy consumption and serious product browning in the high-temperature concentration.
(A) Traditional processing technology of soybean peptides (B) Multi-enzyme step-by-step directional enzymatic hydrolysis technology.
The bitterness and astringency of soybean peptides are additional technical problems that must be overcome during production (Meinlschmidt et al., 2016). It is generally believed that the bitterness of soybean peptides is related to hydrophobic amino acids, traditional debittering treatments greatly reduce the nutritional value of the soybean peptide itself by removing many hydrophobic amino acids (Seo et al., 2008), which may significantly alter the amino acid composition. However, multi-enzyme step-by-step directional enzymatic hydrolysis technology can effectively improve soybean peptides' taste. Specifically, instantaneous high-temperature technology is used first to promote the disintegration of the protein structure, thereby exposing the enzyme-cutting site, and improving enzymatic hydrolysis efficiency (Liu et al., 2016). After that, under pH 8.5, endoproteases are used for the first step of enzymatic hydrolysis to disintegrate the protein structure. The second step is hydrolyzing the long peptide chain using endoproteases at pH 7.5. Next, under pH 6.5, the macromolecular peptides are uniformly hydrolyzed into low molecular weight peptides of between 150 Da to 1000 Da by the endoproteases and neutral proteases whose enzymatic targets are serine (Ser), tyrosine (Tyr), and alanine (Ala). With the deepening of hydrolysis, the system's pH value decreases, and the presequence enzymes become inactivated, avoiding excessive hydrolysis. Finally, under pH 5.5, the ends of the low molecular weight peptide chains are modified by exoproteinase, and the specific bitter amino acid is eliminated from the peptide chain (Fig. 2B).
Gel properties Protein gel refers to the network structure formed between aggregates after protein aggregates, which is one of the proteins' most important functional properties. When the protein forms aggregates, either by heating and/or adding various coagulants (such as acids or salt coagulants), soybean protein heat-induced gel or cold-induced gel is formed (Kohyama et al., 1995; Nishinari et al., 2014). The heat-induced gelation of protein involves its denaturing, unfolding, aggregating, and then further agglomerating and gelating, all of which can co-occur at high protein concentrations, solidifying into a gel after heating and cooling (Renkema and van Vliet, 2004; Nishinari et al., 2014). Conversely, protein aggregation or precipitation can only be formed after heating and cooling when the protein concentration is low. In this case, it is necessary to change the protein system's pH balance or ionic strength by adding other substances to form a gel (Nishinari et al., 2014). Thus, SPI, plays a vital role in food processing because of its good gel properties. Wang et al. (2018) improved the texture of tofu after studying the different conditions under which the gel of SPI is affected and learning that microbial transglutaminase induces tight coagulation in soybean protein. SPI gel has a fine structure and is not bitter, so it has a certain practical application value. SPI is also a commonly used plant protein in processing meat products since it is added to pork, fish, and other products. Adding SPI can improve characteristics such as hardness, elasticity, cohesion, and chewiness under certain conditions, thereby effectively improving the mouthfeel of meat products (Lv et al., 2021; Zhang et al., 2023).
Emulsifying properties Emulsibility refers to the amount of oil that a certain amount of protein can emulsify. The water and oil separation rate of an emulsion during storage usually defines emulsion stability. As an emulsifier, soybean globulin is commonly used to manufacture oil-in-water emulsions (Deng, 2021). The prominent role of the emulsifier in emulsion production is adsorption on the surface of fine droplets to prevent them from coalescing with neighboring droplets to form larger droplets. Thus, denatured globulins at the interface cover the surface of a tiny droplet. In the aqueous phase, the hydrophobic amino acids buried in the globulin protein core are exposed and adsorbed on the surface of the oil droplets, acting as a steric barrier against coalescence and flocculation (McClements and Gumus, 2016; Deng, 2021). Researchers have explored various methods to improve the emulsifying ability of soybean protein. Chove et al. (2007) observed that protein fractions rich in 7S globulin soybean protein subunits exhibited higher functionality in terms of solubility, foaming, and emulsification after their structure had been modified by microfiltration. Wan et al. (2013) improved the stability of SPI-based emulsions by adding resveratrol and stevioside as natural antioxidants. Improving the emulsification of soybean protein isolate can make it more widely applicable to the food industry and exploit the development of new products, such as soybean-based fat and cream.
Textured properties Textured soybean protein, produced by conditioning, texturing, and other processes, has a structure like that of lean meat and is, thus, marketed as a meat substitute, synthetic meat, or plant-based meat (Huang et al., 2022a). The raw materials used in plant-based meat include defatted soybean meal, SPI, SPC, etc. Protein is denatured under high temperature, high pressure, and strong shearing force, during which the protein molecules are aligned in a specific orientation. The spatial arrangement inside the molecule changes (Zhang et al., 2022a). Finally, at the die of the extruder, due to the sudden change in temperature and pressure, the protein molecules interact again in the flow to form textured soybean protein with a meat-like structure (Xia et al., 2023).
The situation of plant-based meat Due to the worldwide demand for health-related eating and the involvement of animal foods and other environmental impacts, the industry has expanded its focus on meat alternatives (Hu et al., 2019; Ahmad et al., 2022). Thus, it is fast becoming a hotspot of global research and investment, with broad commercial prospects. The amino acid composition of soybean protein is close to animal protein. Since it is also inexpensive, it has become the primary raw material in the factory-scale production of plant meat.
Globally, the plant-based meat market is estimated to be worth US$ 7 900 million in 2022 and, with a compound annual growth rate of 14.7 %, is expected to reach US$ 15 700 million by 2027ii). Widespread popularity and demand for plant-based meat products are anticipated to increase significantly in the coming years owing to growing health, ethical and environmental concerns among consumers related to animal-based protein sources (Ahmad et al., 2022; Gbejewoh et al., 2022). Moreover, the COVID-19 pandemic raised additional questions about the safety of animal protein supplies, and plant-based meats have played a significant role in rebuilding the restaurant industry in the aftermath of the global viral health crisis.
Challenges and prospect of soybean protein-based meat The biggest challenge facing plant-based meat is the development of products that suit different regions' tastes and dining habits. Since the United States currently dominates the plant-based meat market, products include mainly meat pies, meatballs, and minced meat. Therefore, the next challenge is the development of products such as meat pieces, ribs, and marbled meat, which are suitable for east Asian cooking methods and preferences (Sun et al., 2021; Nezlek and Forestell, 2022). Currently, the distinctive differences remaining between soybean protein-based meat products and animal meat are manifested mainly in the former's unnatural color, poor moisturization, poor texture, and strong beany flavor (Sun et al., 2021; Starowicz, et al., 2022; Ahmad et al., 2022). Thus, plant-based meat producers must overcome problems relating to structure and taste.
Soybean protein has good process characteristics, as described in section 6. We use SPI to create pork's “fat” and “skin” because of its emulsifying properties. The plant oil is fixed in the o/w “fat” system; the system shows excellent softening in the mouth (Huang et al., 2022a). At the same time, the oil content of “fat” is lower than the real fat. Different SPI content, ingredient, and processes create the “skin,” which can mimic the texture and appearance of natural pork rinds (Zhang et al., 2022b). The gel properties also played a role in processing “fat” and “fascia” between lean tissue. Textured soybean protein used in lean meat also be studied (Yang et al., 2023). Above all, the “fat, skin, fascia, and lean” was assembled by the SPI's gel properties and enzyme support (Li et al., 2020). The whole soybean protein-based meat (Fig. 1B) is an excellent example of the integrated use of soybean protein.
In addition, research direction and product modality differ in the research and application of plant-based meat due to differences in eating habits worldwide. Products that are suitable for local market demand, cooking methods, and eating habits must be developed, not just fast-food products such as hamburgers favored by European and American markets. The discussion of plant-based meat also requires the development of soybean protein suitable for use as a raw material in plant-based meat. Proteins with a light beany flavor, light color, and good cross-linking properties will provide apparent advantages in plant-based meat processing. An in-depth study of the sensory characteristics of artificial meat, which can assist in making it more realistic in terms of vision, taste, smell, and other aspects, is the future research direction for both Chinese and foreign researchers.
Although the composition of SPI has been well understood, the relationship between their structure and processing properties needs further investigation. The removal of SPI anti-nutritional factors transforms it into a protein with relatively good food safety. Furthermore, soybean peptides, an extension product of the soybean protein industry, have a relatively small molecular weight and can be quickly absorbed by the human body. Due to their excellent properties, soybean protein and soybean peptides will have great development prospects in infant food, elderly food, and foods for special medical purpose.
Currently, food for special medical purposes, plant protein beverages, plant-based meat, and related products have relatively high requirements for the taste and quality of soybean protein. Moreover, significant improvements in SPI's palatability and processing adaptability can also improve the application field and scope of plant-derived soybean protein. A more comprehensive application of soybean protein can reduce the dependence on animal protein and improve energy conversion efficiency. Increasing expansion of the plant protein market will simultaneously drive the development of the entire soybean protein industry, promote the extension of the soybean industry chain, and introduce broader prospects and development space to the plant protein industry. Soybean protein offers excellent processing characteristics, low cost, and high nutritional value. However, the capacity and technology of soybean deep processing require further improvement, as do the added value and variety of products and environmental awareness of the industry. Promoting and applying the new soybean protein production process will provide higher quality soybean protein and related products and make the product more environmentally friendly. But until now, certain defects and deficiencies in the application palatability and processing adaptability of soybean protein still hamper its positive comparison with animal protein. Hence, scientific research, technology improvement, product development, and the general equipment used in soybean product deep processing are important to focus areas to ensure the industry's growth and promising development potential.
Conflict of interest There are no conflicts of interest to declare.
