Protease inhibitor activities and isoflavone content in commercial soymilks and soy-based infant formulas sold in Ottawa, Canada

Hypolipidemic Effects of Soy Protein and Isoflavones in the Prevention of Non-Alcoholic Fatty Liver Disease- A Review

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and affects about 25% of the population globally. Obesity and diabetes are the main causes of the disease characterized by excessive accumulation of lipids in the liver. There is currently no direct pharmacological treatments for NAFLD. Dietary intervention and lifestyle modification are the key strategies in the prevention and treatment of the disease. Soy consumption is associated with many health benefits such as decreased incidence of coronary heart disease, type-2 diabetes, atherosclerosis and obesity. The hypolipidemic functions of soy components have been shown in both animal studies and human clinical trials. Dietary soy proteins and associated isoflavones suppressed the formation and accumulation of lipid droplets in the liver and improved NAFLD-associated metabolic syndrome. The molecular mechanism(s) underlying the effects of soy components are mainly through modulation of transcription factors, sterol regulatory element-binding protein-1 and peroxisome proliferator-activated receptor-γ2, and expressions of their target genes involved in lipogenesis and lipolysis as well as lipid droplet-promoting protein, fat-specific protein-27. Inclusion of appropriate amounts of soy protein and isoflavones in the diets might be a useful approach to decrease the prevalence of NAFLD and mitigate disease burden.

Perspective: Soybeans Can Help Address the Caloric and Protein Needs of a Growing Global Population

Feeding a growing global population with projected rising socioeconomic status will require additional sources of calories and especially protein. These sources need to align with the Sustainable Development Goals established by the Food and Agriculture Organization of the United Nations. The soybean is uniquely positioned to meet this challenge based on the following criteria: (1) Global soybean production exceeds by ~4 times the production of all pulses combined (2) Soybeans are higher in protein than other legumes and soy protein quality is similar to animal protein quality (3) Soybeans are an excellent source of healthy fat, including both essential fatty acids (4) Soybeans, like other legumes, symbiotically fix atmospheric nitrogen thereby reducing the need for fertilizer inputs (5) Greenhouse gas emissions per unit protein are lower than for nearly all other foods (6) Soybeans, like other legumes, are also recognized as an affordable food that can be incorporated into diverse diets regardless of economic standing and (7) The range of foods produced from soybeans constitutes an important position in historic and contemporary cuisines, cultures and emerging consumer trends for plant-based protein. Although most soybeans are currently used for animal feed, soybean use is dictated by consumer demand. Therefore, soybeans are well positioned to meet future global needs for energy and protein. Armed with this knowledge, health professionals can feel justified in encouraging greater consumption of soyfoods for both personal and planetary reasons.

Heat-induced unfolding facilitates plant protein digestibility during in vitro static infant digestion

Soy protein is the main protein source for plant-based infant formula, whereas pea protein is considered as a potential alternative plant protein source. This study assessed the structural changes of soy and pea proteins after heating between 65 °C and 100 °C, and its effects on the in vitro digestibility in the context of infant digestion. We found that with increased heating intensity, both soy and pea proteins unfolded, manifested as the increased surface hydrophobicity, thereby potentially improving the accessibility to digestive enzymes. Their final in vitro digestibility increased from ∼ 30% of non-treated samples to ∼ 60% of 100 °C-heated samples for soy protein, and from ∼ 52% to ∼ 65% for pea protein. Surface hydrophobicity was strongly positively correlated to the overall digestibility. Therefore, the heating temperatures that enabled protein unfolding promoted the digestibility of soy and pea proteins under infant digestion conditions.

Effects of dietary active soybean trypsin inhibitors on pancreatic weights, histology and expression of STAT3 and receptors for androgen and estrogen in different tissues of rats

Our previous study showed that soy milks could contain high levels of active soybean trypsin inhibitors (SBTI) if they were not properly processed. This study investigated the effects of consuming active SBTI on pancreatic weights, histology, trypsinogen production and expression of STAT3, receptors for androgen (AR) and estrogen (ER) in pancreas, liver and uterus of rats. Weanling Sprague-Dawley rats were randomly divided into 3 groups (8 females and 8 males/group) and fed diets containing either 20% casein protein (Casein) or 20% soy protein (SP) in the presence of high (1.42 BAEE unit/µg, SP + SBTI) or low (0.2 BAEE unit/µg, SP-SBTI) levels of active SBTI for 8 weeks. Ingestion of SP + SBTI diet markedly increased pancreatic weights and trypsinogen content (p < 0.01), and caused acinar cell hypertrophy, and reduced pancreatic STAT3, p-STAT3, AR and ERβ content, and increased uterine ERα and ERβ compared to the Casein or SP-SBTI diets (p < 0.05). The two SP-containing diets lowered hepatic STAT3, p-STAT3, and pancreatic ERα, and increased hepatic ERα and ERβ content in the female rats compared to the Casein diet (p < 0.05). This study demonstrated for the first time that consumption of high level of active SBTI not only increased pancreatic weights and acinar cell secretions, but also attenuated the expression of pancreatic STAT3, p-STAT3, AR, and ERβ proteins in both sexes and increased uterine ERα and ERβ content, and that dietary soy protein affected hepatic STAT3, p-STAT3, ERα and ERβ in a gender-dependent manner.

Inactivation of Soybean Bowman-Birk Inhibitor by Stevioside: Interaction Studies and Application to Soymilk

In this work, the interaction of the soybean Bowman-Birk inhibitor (BBI) with stevioside (STE) was studied by stopped-flow-fluorescence and molecular docking. STE's inactivation of protease-inhibitor activities in soymilk and the influence of STE addition on the sensory character of soymilk were also evaluated. The results indicate that STE binds BBI with a binding constant ( Ka) of 3.38 × 105 L mol-1 to form a 1:1 complex. The docking study reveals that two hydrogen bonds are formed between the side-chain of Lys16 (reactive site 1) of BBI and the glucose-ring hydroxyl groups of STE, which may block BBI from contacting trypsin and thus deactivate the trypsin-inhibitor activity (TIA) of BBI. Moreover, the residual TIA in soymilk could also be inactivated by STE. A mixture of 159 mg/L STE and 60 g/L sucrose could be used for sweetening soymilk without affecting the sensory characteristics when compared to a reference product sweetened with 9% sucrose.

Comparison of Conventional and Microwave Treatment on Soymilk for Inactivation of Trypsin Inhibitors and In Vitro Protein Digestibility

Soymilk is lower in calories compared to cow’s milk, since it is derived from a plant source (no cholesterol) and is an excellent source of protein. Despite the beneficial factors, soymilk is considered as one of the most controversial foods in the world. It contains serine protease inhibitors which lower its nutritional value and digestibility. Processing techniques for the elimination of trypsin inhibitors and lipoxygenase, which have shorter processing time and lower production costs are required for the large-scale manufacturing of soymilk. In this study, the suitable conditions of time and temperature are optimized during microwave processing to obtain soymilk with maximum digestibility with inactivation of trypsin inhibitors, in comparison to the conventional thermal treatment. The microwave processing conditions at a frequency of 2.45 GHz and temperatures of 70 °C, 85 °C and 100 °C for 2, 5 and 8 min were investigated and were compared to conventional thermal treatments at the same temperature for 10, 20 and 30 min. Response surface methodology is used to design and optimize the experimental conditions. Thermal processing was able to increase digestibility by 7% (microwave) and 11% (conventional) compared to control, while trypsin inhibitor activity reduced to 1% in microwave processing and 3% in conventional thermal treatment when compared to 10% in raw soybean.

Relationship between Glycation and Polyphenol Content and the Bioactivity of Selected Commercial Soy Milks

Soy milk is a health-promoting beverage of which consumption is steadily expanding. Different bioactivities have been associated with soy products such as antioxidant capacity, anti-inflammatory properties, or decrease of cancer development risk. These activities have been related to the presence of several compounds, including polyphenols and serine protease inhibitors, although factors influencing such activities have been scarcely studied. In this study, we have determined the antioxidant capacity (ABTS and FRAP methods measured with the global antioxidant response, GAR protocol), total phenolic content, serine protease inhibitory activity, and presence of heat damage indicators in commercial soy milks. Polyphenols were primarily responsible for the antioxidant capacity of soy milks, increasing their concentration after digestion. Glycation under heat treatment might be responsible for decreasing protease inhibitory activities in soy milks. The results obtained support a role for furosine, a known marker of Maillard reaction and glycation, as a potential indicator to monitor both thermal treatment and effects on protease inhibitory activities in soy milk. The contribution of soy milk consumption to the daily intake of antioxidants and serine protease inhibitory activities is discussed.

Isoflavone content and profile comparisons of cooked soybean-rice mixtures: electric rice cooker versus electric pressure rice cooker

This study examined the effects of heat and pressure on the isoflavone content and profiles of soybeans and rice cooked together using an electric rice cooker (ERC) and an electric pressure rice cooker (EPRC). The total isoflavone content of the soybean-rice mixture after ERC and EPRC cooking relative to that before cooking was ∼90% in soybeans and 14-15% in rice. Malonylglucosides decreased by an additional ∼20% in EPRC-cooked soybeans compared to those cooked using the ERC, whereas glucosides increased by an additional ∼15% in EPRC-cooked soybeans compared to those in ERC-cooked soybeans. In particular, malonylgenistin was highly susceptible to isoflavone conversion during soybean-rice cooking. Total genistein and total glycitein contents decreased in soybeans after ERC and EPRC cooking, whereas total daidzein content increased in EPRC-cooked soybeans (p < 0.05). These results may be useful for improving the content of nutraceuticals, such as isoflavones, in soybeans.

Quantitative determination of active Bowman-Birk isoinhibitors, IBB1 and IBBD2, in commercial soymilks

Naturally-occurring serine protease inhibitors of the Bowman-Birk family exert their potential chemopreventive and/or therapeutic properties via protease inhibition. In this study, we have quantified the amounts of active BBI isoinhibitors, IBB1 and IBBD2, in six commercial soymilks. By using cation exchange chromatography, the BBI isoinhibitors were isolated and their specific trypsin inhibitory activity was used to estimate their amounts in soymilk samples. IBB1 and IBBD2 concentrations ranged from 0.44 to 5.20 and 0.27 to 4.60 mg/100ml of soymilk, respectively; total BBI, considered as the sum of both isoinhibitors, ranged from 0.60 to 9.07 mg/100ml of soymilk. These data show that physiologically relevant amounts of active BBI are present in commercial soymilk and may exert potential health-promoting effects.

Determination of isoflavones in rat serum using liquid chromatography-tandem mass spectrometry with a highly efficient core-shell column

Consumption and nutritional supplementation of soy and soy-based products have been linked to health benefits such as lower cholesterol and triglyceride levels, and decreased incidence of cardiovascular disease and diabetes. In this study, we have developed a sensitive, specific, and robust method using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for determination of serum isoflavones. A new highly efficient pentafluorophenyl phase core-shell column was first used to separate all isoflavones within 3 min, a separation time which is comparable to ultra-pressure liquid chromatography (UPLC) and micro-HPLC. A two-enzyme hydrolysis system with sulfatase and β-glucuronidase has also been developed to improve the efficiency of deconjugation of conjugated isoflavones in serum. The corresponding conjugated isoflavones were used to evaluate recoveries. In addition to duplicates, the method of standard addition was also applied in sample analysis for quality control. The developed method was applied to the analysis of 32 serum samples and was shown to be specific, sensitive and reproducible.

Bowman-Birk and Kunitz protease inhibitors among antinutrients and bioactives modified by germination and hydrolysis in Brazilian soybean cultivar BRS 133

Soybean contains constituents that have antinutritional and bioactive properties. Enzymatic hydrolysis and germination can enhance the biological activity of these compounds in soybean. The objective of this study was to investigate the effect of germination, Alcalase (protease) hydrolysis, and their combination on the concentrations of antinutritional and bioactive compounds in Brazilian soybean cultivar BRS 133. A combination of germination and Alcalase hydrolysis resulted in the degradation of Bowman-Birk inhibitor (BBI), Kunitz trypsin inhibitor (KTI), and lunasin by 96.9, 97.8, and 38.4%. Lectin was not affected by any of the processing treatments when compared to nongerminated and nonhydrolyzed soy protein extract. Total isoflavones (ISF) and total saponins (SAP) increased by 16.2 and 28.7%, respectively, after 18 h of germination, while Alcalase hydrolysis led to the reduction of these compounds. A significant correlation was found between concentrations of BBI and KTI, BBI and lunasin, BBI and ISF, KTI and lunasin, KTI and ISF, KTI and SAP, lunasin and ISF, and ISF and SAP. Germination and Alcalase hydrolysis interacted in reducing BBI, ISF, and SAP. This study presents a process of preparing soy flour ingredients with lower concentrations of antinutritional factors and with biologically active constituents, important for the promotion of health associated with soybean consumption. In conclusion, 18 h of germination and 3 h of Alcalase hydrolysis is recommended for elimination of protease inhibitors, while bioactives are maintained by at least 50% of their original concentrations.