Health-promoting activities of ultra-filtered okara protein hydrolysates released by in vitro gastrointestinal digestion: identification of active peptide from soybean lipoxygenase

Structures, antioxidant, and angiotensin I-converting enzyme (ACE)-inhibitory activities of peptides derived from protein hydrolysates of three phenolics-rich legume genera

Lentil, black soybean, and black turtle bean are rich in phenolic antioxidants but belong to different scientific genera with different protein structures. This study's objective was to compare the characteristics of peptides derived from the protein hydrolysates of these legumes. Proteins were isolated, cooked, and subjected to in vitro digestion with pepsin, trypsin, and chymotrypsin. Hydrolyzed peptides were fractionated by ultrafiltration (UF), anion-exchange chromatography, and gel-permeation chromatography (GPC). GPC-eluted peptides of <3 kDa with high angiotensin I-converting enzyme (ACE)-inhibitory activities were sequenced. Antioxidant profiles of peptides from the three legumes analyzed by five methods did not follow the same activity patterns associated with the decreases in peptide's molecular size. Among the UF fractions, the <3 kDa fraction had the highest ACE-inhibition with approximately 45%, 42%, and 39% at 100 µg/mL. Stepwise purifications of the hydrolysates enhanced the ACE-inhibitory capacity (IC50) by two to nine folds after GPC to approximately 85, 64, and 93 µg/mL for lentil, black soybean, and black turtle bean, respectively. The 210 peptides sequenced in the <3 kDa fractions had chain-lengths, ranging from 6 to 18 amino acids with lentil having the shortest average length of 7.7 per peptide. Overall, based on chemical analyses, peptides contributed higher antioxidant capacity and ACE-inhibition than phenolics in legumes. Black turtle bean may need to be heated more prior to consumption to achieve the same digestibility as lentil and soy proteins. Results provided a foundation for making bioactive peptides from the three legumes. PRACTICAL APPLICATION: Three antioxidant-rich legume genera, lentil, black soybean, and black turtle bean, produced different peptides with different angiotensin I-converting enzyme (ACE) potencies and different peptide lengths. The results provided a scientific basis for producing peptides from the selected genera for the development of functional foods or dietary supplement with high antioxidant, ACE inhibitory activities, and digestibility.

Production of Protein Hydrolysates Teff (Eragrostis tef) Flour with Antioxidant and Angiotensin-I-Converting Enzyme (ACE-I) Inhibitory Activity Using Pepsin and Cynara cardunculus L. Extract

In recent years, several studies have shown the antioxidant and antihypertensive potential of bioactive peptides. Thus, bioactive peptides are likely to be a valuable substance for the development of functional foods. There are a wide variety of sources of these peptides, including several cereals. Teff is an Ethiopian-rooted cereal with an interesting nutritional profile, mainly due to its high amount of protein. In this study, teff flour was subjected to a defatting process for optimizing the protein extraction. Such extraction was performed by precipitation from its isoelectric point, a crucial step that separates the protein from other components based on their charge. The protein obtained was subjected to enzymatic hydrolysis by pepsin and Cynara cardunculus L. The antihypertensive (angiotensin-I-converting enzyme -ACE-I- inhibitory activity) and antioxidant activity (2,2-diphenyl-1-picrylhydrazyl -DPPH- radical scavenging activity) of the peptides were determined. According to the IC50 values, the results obtained showed that the peptides from teff flour show promising bioactivity compared to other cereals. Furthermore, the peptides from teff flour obtained from C. cardunculus L. showed higher antioxidant activity (defatted teff flour -DTF-: 0.59 ± 0.05; protein extract -EP- : 1.04 ± 0.11) than those obtained with pepsin (DTF: 0.87 ± 0.09; EP: 1.73 ± 0.11). However, C. cardunculus L. hydrolyzate peptides showed lower inhibitory activity of ACE-I (DTF: 0.59 ± 0.07; EP: 0.61 ± 0.05) than the pepsin hydrolyzate (DTF: 0.15 ± 0.02; EP: 0.33 ± 0.05).

Valorization of Okara by Enzymatic Production of Anti-Fungal Compounds for Plant Protection

Okara is a soybean transformation agri-food by-product, the massive production of which currently poses severe disposal issues. However, its composition is rich in seed storage proteins, which, once extracted, can represent an interesting source of bioactive peptides. Antimicrobial and antifungal proteins and peptides have been described in plant seeds; thus, okara is a valuable source of compounds, exploitable for integrated pest management. The aim of this work is to describe a rapid and economic procedure to isolate proteins from okara, and to produce an enzymatic proteolyzed product, active against fungal plant pathogens. The procedure allowed the isolation and recovery of about 30% of okara total proteins. Several proteolytic enzymes were screened to identify the proper procedure to produce antifungal compounds. Antifungal activity of the protein digested for 24 h with pancreatin against Fusarium and R. solani mycelial growth and Pseudomonas spp was assessed. A dose-response inhibitory activity was established against fungi belonging to the Fusarium genus. The exploitation of okara to produce antifungal bioactive peptides has the potential to turn this by-product into a paradigmatic example of circular economy, since a field-derived food waste is transformed into a source of valuable compounds to be used in field crops protection.

Hairless canary seeds (Phalaris canariensis L.) as a potential source of antioxidant, antihypertensive, antidiabetic, and antiobesity biopeptides

Rising consumer concerns with synthetic drugs to treat non-communicable diseases (NCDs) have promoted a shift towards using natural biological active constituents that offer similar health benefits. Hairless canary seed (Phalaris canariensis L) is an emerging crop traditionally used in Mexico to treat NCDs. Peptides liberated during simulated digestion of canary seed protein are believed to be responsible for their biological activity; however, no studies have shown the effect of controlled protein hydrolysis using commercial proteases on canary seed protein’s biological activity. Therefore, this study aimed to explore the in vitro antihypertensive, antidiabetic, and anti-obesity activity of canary seed peptides derived from proteolysis with Alcalase®. Protein fractions were primarily composed of prolamins (54.07 ± 1.8%), glutelins (32.19 ± 3.18%), globulins (5.97 ± 0.52%) and albumins (5.97 ± 0.52%). The < 3 kDa and 3–10 kDa peptide fractions showed the highest inhibition capacity (p < 0.05) towards angiotensin-converting enzyme (IC50= 0.028–0.032 mg/mL) lipase (IC50= 2.15–2.27 mg/mL), α-glucosidase (IC50= 0.82–1.15 mg/mL), and dipeptidyl-peptidase-IV (IC50= 1.27–1.60 mg/mL). Additionally, these peptide fractions showed high antioxidant activity against DPPH (134.22–150.66 μmol TE/mg) and ABTS (520.92–813.33 μmol TE/mg). These results provide an insight into the potential development of functional foods using commercial enzymatic hydrolysis of canary seed proteins for treating hypertension, type-2 diabetes, and obesity.

Prebiotic Impacts of Soybean Residue (Okara) on Eubiosis/Dysbiosis Condition of the Gut and the Possible Effects on Liver and Kidney Functions

Okara is a white-yellow fibrous residue consisting of the insoluble fraction of the soybean seeds remaining after extraction of the aqueous fraction during the production of tofu and soymilk, and is generally considered a waste product. It is packed with a significant number of proteins, isoflavones, soluble and insoluble fibers, soyasaponins, and other mineral elements, which are all attributed with health merits. With the increasing production of soy beverages, huge quantities of this by-product are produced annually, which poses significant disposal problems and financial issues for producers. Extensive studies have been done on the biological activities, nutritional values, and chemical composition of okara as well as its potential utilization. Owing to its peculiar rich fiber composition and low cost of production, okara might be potentially useful in the food industry as a functional ingredient or good raw material and could be used as a dietary supplement to prevent varied ailments such as prevention of diabetes, hyperlipidemia, obesity, as well as to stimulate the growth of intestinal microbes and production of microbe-derived metabolites (xenometabolites), since gut dysbiosis (imbalanced microbiota) has been implicated in the progression of several complex diseases. This review seeks to compile scientific research on the bioactive compounds in soybean residue (okara) and discuss the possible prebiotic impact of this fiber-rich residue as a functional diet on eubiosis/dysbiosis condition of the gut, as well as the consequential influence on liver and kidney functions, to facilitate a detailed knowledge base for further exploration, implementation, and development.

Valorisation of By-Products from Soybean (Glycine max (L.) Merr.) Processing

In recent years, increased awareness of the health benefits associated with consuming soy-based foods, knowledge of milk-related allergies and a move towards more sustainable food production have led to an increase in the number of available soy-based products. The biggest producers in the world, the USA, South America and China, are from the Pacific region. This enormous production is accompanied by the accumulation of related by-products, in particular, a substance that is known as okara. Okara is a paste that is rich in fibre (50%), protein (25%), fat (10%), vitamins and trace elements. Its proper use would lead to economic advantages and a reduction in the potential for polluting the environment. Its high fibre content and low production costs mean that it could also be used as a dietary supplement to prevent diabetes, obesity and hyperlipidaemia. Chemical or enzymatic treatment, fermentation, extrusion, high pressure and micronisation can all increase the soluble fibre content, and thus improve nutritional quality and processing properties. However, the product also degrades rapidly due to its high moisture content (70-80%), which makes it difficult to handle and expensive to dry by conventional means. The aim of this paper is therefore to thoroughly study the existing literature on this subject in order to develop a general protocol for okara exploitation and valorisation. A cost/benefit analysis could drive the design of eco-friendly, sustainable protocols for the preparation of high-value nutritional products.

Protease technology for obtaining a soy pulp extract enriched in bioactive compounds: isoflavones and peptides

This work presents a new bioprocess process for the extraction of bioactive components from soy pulp by-product (okara) using an enzymatic technology that was compared to a conventional water extraction. Okara is rich in fiber, fat, protein, and bioactive compounds such as isoflavones but its low solubility hampers the use in food and fertilizer industry. After the enzymatic attack with endoproteases half of the original insoluble proteins were converted into soluble peptides. Linked to this process occured the solubilization of isoflavones trapped in the insoluble protein matrix. We were able to extract up to 62.5% of the total isoflavones content, specially aglycones, the more bioactive isoflavone forms, whose values rose 9.12 times. This was probably due to the increased solubilization and interconversion from the original isoflavones. In conclusion, our process resulted in the formulation of a new functional product rich in aglycones and bioactive peptides with higher antioxidant potency than the original source. Therefore, we propose that the enzymatic extraction of okara bioactive compounds is an advantageous tool to replace conventional extraction.

Purification and Characterization of Antioxidant Peptides from Alcalase-Hydrolyzed Soybean ( Glycine max L.) Hydrolysate and Their Cytoprotective Effects in Human Intestinal Caco-2 Cells

This study aimed to purify and identify antioxidant peptides from the low-molecular-weight fraction (SPH-I, MW < 3 kDa) of Alcalase-hydrolyzed soybean ( Glycine max L.) hydrolysate and further evaluate the cytoprotective effects of synthesized peptides against oxidative stress in human intestinal Caco-2 cells. After purification by gel filtration chromatography and reversed-phase HPLC, four major peptides were sequenced by nano-LC-ESI-MS/MS as VVFVDRL (847 Da, SPH-IA), VIYVVDLR (976 Da, SPH-IB), IYVVDLR (877 Da, SPH-IC), and IYVFVR (795 Da, SPH-ID). The antioxidant peptides were synthesized and displayed desirable DPPH radical-scavenging activity (from 16.5 ± 0.5 to 20.3 ± 1.0 μM Trolox equivalent (TE)/μM), ABTS•+ radical-scavenging activity (from 3.42 ± 0.2 to 4.24 ± 0.4 mM TE/μM), ORAC (from 143 ± 2.1 to 171 ± 4.8 μM TE/μM), and FRAP (from 54.7 ± 1.2 to 79.0 ± 0.6 mM Fe2+/μM). Moreover, the synthesized peptides protected Caco-2 cells against H2O2-induced oxidative damage via significantly downregulating intracellular ROS generation and lipid peroxidation ( p < 0.05). Additionally, SPH-IC and SPH-ID statistically upregulated total reduced glutathione synthesis, enhanced activities of catalase and glutathione reductase, and suppressed ROS-mediated inflammatory responses via inhibiting interleukin-8 secretion ( p < 0.05).

Cationic peptides from enzymatic hydrolysates of soybean proteins exhibit LPS-neutralizing and angiogenic activities

In this study, we prepared fractions containing multifunctional cationic peptides by separating the commercial soybean protein hydrolysate Hinute-AM into 20 fractions. These fractions contained peptides with various isoelectric points (pI), as indicated by ampholyte-free isoelectric focusing (autofocusing). Thus, we purified and identified the cationic peptides from fractions 19 and 20, which had pH values greater than 10, using reversed-phase high-performance liquid chromatography and matrix-assisted laser/desorption ionization-time-of-flight mass spectroscopy. Among 19 identified cationic peptides, NKNAKPPSPR, PGKKNAIV, KSGPGMSPR, NVSKPPRVV, RKVGAGGRKPLG, and LPCVIGGVPKRV had high pI values and were included as chemically synthesized peptides in assays of various functions, including lipopolysaccharide (LPS)-neutralizing and angiogenic activities. Chromogenic LPS-neutralizing assays using Limulus amebocyte lysates showed that 50% effective concentrations of these six peptides were between 1.63 and 2.65 μM, and were higher than that (0.12 μM) of polymyxin B. Moreover, in tube-formation assays in human umbilical vein endothelial cells, all of the six cationic peptides except LPCVIGGVPKRV exhibited angiogenic activities similar to those of the positive control LL-37. In addition, the six identified cationic peptides had no hemolytic activity at concentrations up to 500 μM in mammalian red blood cells. Our results demonstrate that five of the identified cationic peptides, excluding LPCVIGGVPKRV, have multiple functions and little or no hemolytic activity. These data indicate that fractions containing cationic peptides from Hinute-AM have the potential to be used as dietary supplements and functional ingredients in food products.

Biotransformation with cellulase, hemicellulase and Yarrowia lipolytica boosts health benefits of okara

Okara (soybean residue) is a highly perishable food processing by-product from soymilk and tofu manufacture. It contains a large proportion of insoluble dietary fibre (40-60% on a dry basis), as well as digestion-resistant proteins, trypsin inhibitors and phytic acid. These factors contribute lead to the under-utilisation of okara. To improve the overall nutritional quality of okara, sequential saccharification of okara by Celluclast® 1.5L (cellulase) or Viscozyme® L (cellulase and hemicellulase) and fermentation by the yeast Yarrowia lipolytica were performed. The changes in the antioxidant capacity, amino acids, phenolic acids, isoflavones, phytic acid and dietary fibre during biotransformation were studied. Carbohydrase pre-treatment increased the amounts of monosaccharides, trans-cinnamic acid and aglycone isoflavones in okara. After fermentation, the okara had higher antioxidant activity and greater amounts of total amino acids and ferulic acid. Some positive interactions between the carbohydrase and Y. lipolytica were hypothesised: the carbohydrase and Y. lipolytica proteases could have synergised with each other to break down the okara secondary cell wall more efficiently. After 52 h, Celluclast® 1.5 L and Viscozyme® L significantly reduced the insoluble dietary fibre content from 61.9 ± 0.6 to 45.6 ± 3.0% and 24.7 ± 0.3%, respectively (all w/w, dry basis), while increasing the soluble dietary fibre content by about onefold. Both carbohydrases also increased the amounts of monosaccharides, trans-cinnamic acid, and aglycone isoflavones in okara. The addition of Y. lipolytica led to a higher antioxidant capacity and greater amounts of total amino acids and ferulic acid in okara. The overall improvements in the digestibility and potential health benefits of okara highlight the promising applicability of biotransformation in okara valorisation.

Identification and characterization of multifunctional cationic and amphipathic peptides from soybean proteins

In this study, we identified and chemically synthesized three cationic and amphipathic peptides (Glycinin-17, BCAS-16, and BCBS-11) from soybean proteins. These peptides had high isoelectric points, high positive net charges, and included multiple hydrophobic amino acids. Subsequently, we identified multiple functions of these peptides, including antimicrobial, lipopolysaccharide-neutralizing, and angiogenic activities, and examined their cytotoxic activities against mammalian red blood cells. Glycinin-17, BCAS-16, and BCBS-11 exhibited antimicrobial activity against Porphyromonas gingivalis and Candida albicans whereas Glycinin-17 did not possess antimicrobial effects on Propionibacterium acnes and Streptococcus mutans. Membrane-depolarization assays and flow cytometric analyses showed that the antimicrobial properties of Glycinin-17, BCAS-16, and BCBS-11 against P. gingivalis, P. acnes, and S. mutans were dependent on membrane-disrupting potential. In contrast, major antimicrobial activities of these peptides against C. albicans were dependent on interactions with targets other than cell membranes. Furthermore, chromogenic Limulus amebocyte lysate assays showed that 50% effective concentrations (EC50 , 0.12-0.31 μM) of these three peptides neutralize LPS with similar potency (EC50 : 0.11 μM) to that of polymyxin B. Moreover, tube-formation assays in human umbilical vein endothelial cells showed similar angiogenic activities of the three peptides as that following treatment with LL-37. Although BCAS-16 exhibited hemolytic activity, the rate of hemolysis for Glycinin-17 and BCBS-11 in the presence of 500-μM Glycinin-17 and BCBS-11 was less than 2%. These results demonstrate that cationic and amphipathic peptides from soybean proteins, particularly Glycinin-17 and BCBS-11, have potential as multifunctional ingredients for healthcare applications.

Okara (soybean residue) biotransformation by yeast Yarrowia lipolytica

Okara, or soybean residue, is a soy food processing by-product from the manufacture of soymilk and soybean curd (tofu). In this study, solid-state fermentation of okara was conducted over 5days using yeast Yarrowia lipolytica, and the changes in proximate composition, antioxidant capacity, non-volatiles and volatiles were investigated. Yeast metabolism of okara significantly increased the amounts of lipid, succinate and free amino acids and enhanced the antioxidant capacity. In particular, there was a marked increase in important umami tastants after fermentation, with 3-fold increase in succinate and a 20-fold increase in glutamate. The final fermented okara contained 3.37g succinate and 335mg glutamate/100g dry matter. Aldehydes and their derived acids in the fresh okara were catabolised by Y. lipolytica mainly to methyl ketones, leading to a reduced grassy off-odour and a slightly pungent, musty and cheese-like odour in the fermented okara. Amino acid-derived volatiles, such as 3-methylbutanal and 2-phenylethanol, were also produced. Overall, the okara fermented by Y. lipolytica had a greater amount of umami-tasting substances, a cheese-like odour, improved digestibility and enhanced antioxidant capacity. These changes highlight the potential of Yarrowia-fermented okara as a more nutritious, savoury food product or ingredient. Y. lipolytica was thus demonstrated to be suitable for the biovalorisation of this soy food processing by-product.

Food-derived immunomodulatory peptides

Food proteins contain specific amino acid sequences within their structures that may positively impact bodily functions and have multiple immunomodulatory effects. The functional properties of these specific sequences, also referred to as bioactive peptides, are revealed only after the degradation of native proteins during digestion processes. Currently, milk proteins have been the most explored source of bioactive peptides, which presents an interesting opportunity for the dairy industry. However, plant- and animal-derived proteins have also been shown to be important sources of bioactive peptides. This review summarizes the in vitro and in vivo evidence of the role of various food proteins as sources of immunomodulatory peptides and discusses the possible pathways involving these properties. © 2016 Society of Chemical Industry.

Secondary Structure and Subunit Composition of Soy Protein In Vitro Digested by Pepsin and Its Relation with Digestibility

In the present study, in vitro digestibility and structure of soybean protein isolates (SPIs) prepared from five soybean varieties were investigated in simulated gastric fluid (SGF), using FT-IR microspectroscopy and SDS-PAGE. The result indicated that β-conformations were prone to be hydrolyzed by pepsin preferentially and transformed to unordered structure during in vitro digestion, followed by the digestion of α-helix and unordered structure. A negative linear correlation coefficient was found between the β-conformation contents of five SPIs and their in vitro digestibility values. The intensities of the protein bands corresponding to 7S and 11S fractions were decreased and many peptide bands appeared at 11~15 kDa during enzymatic hydrolysis. β-conglycinin was poorly hydrolyzed with pepsin, especially the β-7S subunit. On the other hand, basic polypeptides of glycinin degraded slower than acidic polypeptides and represented a large proportion of the residual protein after digestion. 11S-A₃ of all SPIs disappeared after 1 h digestion. Moreover, a significant negative linear correlation coefficient (r = −0.89) was found between the β-7S contents of five SPIs and their in vitro digestibility values. These results are useful for further studies of the functional properties and bioactive properties of these varieties and laid theoretical foundations for the development of the specific functional soy protein isolate.

The Structure-Activity Relationship of the Antioxidant Peptides from Natural Proteins

Peptides derived from dietary proteins, have been reported to display significant antioxidant activity, which may exert notably beneficial effects in promoting human health and in food processing. Recently, much research has focused on the generation, separation, purification and identification of novel peptides from various protein sources. Some researchers have tried to discover the structural characteristics of antioxidant peptides in order to lessen or avoid the tedious and aimless work involving the ongoing generated peptide preparation schemes. This review aims to summarize the current knowledge on the relationship between the structural features of peptides and their antioxidant activities. The relationship between the structure of the precursor proteins and their abilities to release antioxidant fragments will also be summarized and inferred. The preparation methods and antioxidant capacity evaluation assays of peptides and a prediction scheme of quantitative structure–activity relationship (QSAR) will also be pointed out and discussed.

Mineral elements, lipoxygenase activity, and antioxidant capacity of okara as a byproduct in hydrothermal processing of soy milk

Minerals and antioxidative capacity of raw okara that was obtained as a byproduct from six soybean varieties during hydrothermal cooking (HTC) of soy milk were assessed. Lipoxygenase (Lox), an enzyme deteriorating the sensory characteristics of okara, was also investigated. All genotypes had very similar concentrations of Lox (4.32-5.62%). Compared to raw soybeans, the applied HTC significantly reduced Lox content in okara (0.54-0.19%) and lowered its activity to 0.004-0.007 μmol g(-1) min (-1). Correlation between the content of Lox in soybeans and that in okara (r = 0.21;p < 0.05) was not registered. This indicates that the content of this enzyme in okara depended much more on the technological process than on soybean genotype. Very strong correlation (r = 0.99; p < 0.05) between okara Lox content and its activity was found. The most abundant minerals in raw okara were potassium (1.04-1.21 g/100g), phosphorus (0.45-0.50 g/100 g), calcium (0.26-0.39 g/100 g), and iron (5.45-10.95 mg/100 g). A very high antioxidant capacity (19.06-29.36 mmol Trolox kg(-1)) contributes to the nutritional value of raw okara.

Antihypertensive peptides: production, bioavailability and incorporation into foods

Bioactive food peptides are encrypted within the sequence of food proteins but can be released during food processing (by enzymatic hydrolysis or fermentation) or during gastrointestinal transit. Among bioactive food peptides, those with antihypertensive activity are receiving special attention due to the high prevalence of hypertension in the Western countries and its role in cardiovascular diseases. This paper reviews the current literature on antihypertensive food peptides, focusing on the main methodologies for their production, such as enzymatic hydrolysis, fermentation and the use of recombinant bacteria. This paper also describes the structure/activity relationship of angiotensin-converting enzyme (ACE)-inhibitory peptides, as well as their bioavailability, physiological effects demonstrated by both in vitro and in vivo assays, and the contribution of mechanisms of action other than ACE inhibition. Finally, current reported strategies for incorporation of antihypertensive peptides into foods and their effects on both availability and activity are revised in this manuscript.

Seaweed as a source of novel nutraceuticals: sulfated polysaccharides and peptides

Seaweeds and seaweed-derived products are underexploited marine bioresources and a source of natural ingredients for functional foods. Nutritional studies on seaweeds indicate that brown and red seaweeds possess a good nutritional quality and could be used as an alternative source of dietary fiber, protein, and minerals. Moreover, bioactive sulfated polysaccharides are the main components of soluble fiber in seaweeds and also bioactive peptides can be prepared from seaweed protein. This chapter gives an overview of the main biological properties of sulfated polysaccharides and peptides from brown and red seaweeds. Recent studies have provided evidence that sulfated polysaccharides from seaweeds can play a vital role in human health and nutrition. Besides, peptides derived from algal protein are most promising as antihypertensive agents. Further research work, especially in vivo studies, are needed in order to gain a better knowledge of the relation structure-function by which bioactive compounds from seaweeds exert their bioactivity.