An approach to improve ACE-inhibitory activity of casein hydrolysates with plastein reaction catalyzed by Alcalase

Casein hydrolysate in naturally-fermented buckwheat sourdough: Effects on fermented and physicochemical characteristics, texture, and bacterial microbial composition

The effect of a casein hydrolysate (CH) on the fermentation and quality of a naturally-fermented buckwheat sourdough (NFBS) were investigated, through assessing the fermentation characteristics, carbohydrate and protein degradation, texture, and bacterial composition of NFBS. According to the assaying data, CH might both increase the amount of lactic acid bacteria by 2.62 % and shorten the fermentation period by at least 3 h, subsequently leading to enhanced degradation of carbohydrate and protein, accompanied by a softer texture. More importantly, CH increased the relative abundance of lactobacillus in NFBS, making it the dominant bacterial genus and inhibited the growth of spoilage bacteria. In addition, Spearman correlation analysis indicated that the pH value, lactic and acetic acid contents, carbohydrates, protease activity, and these textural indices like hardness, elasticity, and adhesion had a positive/negative correlation with the bacterial composition of NFBS (Spearman correlation coefficient: -0.93-0.95). CH was thus regarded to be helpful to NFBS processing and production mainly by shortening its fermentation time, improving its fermentation performance, causing a finer texture and microstructure, and changing bacterial composition.

Impact of the Plastein Reaction of Casein Hydrolysates in the Presence of Exogenous Amino Acids on Their Anti-Inflammatory Effect in the Lipopolysaccharide-Stimulated Macrophages

In this study, papain-generated casein hydrolysates (CH) with a degree of hydrolysis of 13.7% were subjected to a papain-mediated plastein reaction in the absence or presence of one of the exogenous amino acids-Gly, Pro, and Hyp-to prepare four plastein modifiers, or mixed with one of three amino acids to prepare three mixtures. The assay results confirmed that the reaction reduced free NH2 for the modifiers and caused amino acid incorporation and peptide condensation. When RAW264.7 macrophages were exposed to the CH, modifiers, and mixtures, these samples promoted macrophage growth and phagocytosis in a dose-dependent manner. In addition, the CH shared similar activity in the cells as the mixtures, while the modifiers (especially the PCH-Hyp prepared with Hyp addition) exerted higher potential than CH, the mixtures, and PCH (the modifier prepared without amino acid addition). The plastein reaction thus enhanced CH bioactivity in the cells. When RAW264.7 macrophages were stimulated with lipopolysaccharide (LPS), the inflammatory cells produced more lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) formation, and caused more four inflammatory mediators (NO, PGE2, TNF-α, and IL-6) and two anti-inflammatory mediators (TGF-β1 and IL-10). However, the PCH-Hyp, PCH, and CH at dose levels of 100 μg/mL could combat against the LPS-induced inflammation. Overall, the PCH-Hyp was more active than the CH and PCH in reducing LDH release, ROS formation, and the secretion of these inflammatory mediators, or in increasing the secretion of the anti-inflammatory mediators. The qPCR and Western blot analysis results further confirmed that these samples had anti-inflammatory effects on the stimulated cells by suppressing the LPS-induced activation of the NF-κB signaling pathway, via regulating the mRNA/miRNA expression of iNOS, IL-6, TNF-α, IL-1β, COX-2, TLR4, IL-10, TGF-β1, miR-181a, miR-30d, miR-155, and miR-148, as well as the protein expression of MyD88, p-IKKα, p-IκBα, p-NF-κB p65, and iNOS, involved in this signaling pathway. In addition, the immunofluorescence assay results revealed that these samples could block the LPS-mediated nuclear translocation of the p65 protein and displayed the same function as the NF-κB inhibitor BAY 11-7082. It was concluded that CH could be endowed with higher anti-inflammatory activity to the macrophages by performing a plastein reaction, particularly that in the presence of exogenous Hyp.

Bitterness of fish protein hydrolysate and its debittering prospects

Fish processing by-products often generated as discard can enzymatically be processed into a product known as fish protein hydrolysates (FPH). FPH is a good source of amino acid and peptides with bioactivities. FPH can be added to foods to improve nutritive values and bioactivities. However, bitterness in FPH, associated with hydrophobicity, degree of hydrolysis, molecular weight, proline residues, type of enzymes, and amino acid sequences has limited its uses in foods. Thus, FPH is used in foods at low levels. Numerous procedures such as extraction with alcohol, activated carbon treatment, Maillard reaction, cyclodextrin, chromatographic separation, and enzymatic hydrolysis with exopeptidase and plastein reaction have been explored to remove the bitterness of FPH. These methods can lower bitterness and improve its taste. However, changes in structure and loss of some peptides may occur. FPH with less or no bitterness can therefore be used at higher levels to alleviate nutrition deficiencies in foods. PRACTICAL APPLICATIONS: Fish protein hydrolysate (FPH) is a nutritive ingredient, which can be produced from fish processing by-products. However, bitterness in FPH has limited its potential use as a nutritive ingredient. As a result, it is incorporated into foods at low levels. Nevertheless, application of several reported debittering processes could assist to solve the problem of bitterness in FPH. The debittering can improve sensory property of FPH, thus widening its utilization.

Effect of the Plastein Reaction in Presence of Extrinsic Amino Acids on the Protective Activity of Casein Hydrolysate against Ethanol-Induced Damage in HHL-5 Cells

Casein hydrolysates (CH) were prepared using papain and modified by the plastein reaction (CH-P) in the presence of extrinsic phenylalanine (CH-P-Phe) or tryptophan (CH-P-Trp). The in vitro protective activity of CH and its modified products against ethanol-induced damage in HHL-5 cells was investigated. The results showed that the modification by the plastein reaction reduced the amino group content of CH. However, the modification by the plastein reaction in the presence of extrinsic amino acids could enhance the antioxidant, proliferative, cell cycle arresting, and anti-apoptosis activity of CH. Biological activities of CH and its modified products in the HHL-5 cells varied depending on the hydrolysate concentration (1, 2, and 3 mg/mL) and treatment time (24, 48, and 72 h). Generally, higher biological activities were found after cell treatment with CH or its modified products at concentration of 2 mg/mL for 48 h compared to other treatments. In addition, CH modified in the presence of tryptophan (CH-P-Trp) showed higher biological activity than that modified in the presence of phenylalanine (CH-P-Phe). Based on the obtained results, it can be concluded that casein hydrolysates with enhanced biological activity and potential health benefits can be produced by papain and the plastein reaction with the incorporation of extrinsic amino acids.

Plastein reaction enhanced bile-acid binding capacity of soybean protein hydrolysates and whey protein hydrolysates

Plastein reaction is a modification reaction that can improve the functional properties of protein hydrolysate. The product of the reaction is a thixotropic aggregation of peptides. This study investigated the formation condition of soybean-whey plastein and bile acid binding capacity of plastein. Soy protein and whey protein were hydrolyzed by pepsin. The mixture (1:1, w/w) of two hydrolysates was modified by pepsin again. After the reaction, the decrease in free amino groups and the turbidity of the modified hydrolysate were measured to obtain appropriate reaction condition. Results showed that the concentration of hydrolysates 40% (w/v), enzyme ratio of 2.0 KU/g protein, pH 5.0, 37 °C, reaction time of 3.0 h respectively, were showed maximum changes in protein hydrolysates. Tricine SDS-PAGE analysis under denaturing conditions revealed that whey protein was more sensitive to pepsin and yielded different polypeptides (PPs) of molecular weight ranged from 3.5-17 kDa. However, a high molecular weight PP was completely hydrolyzed while PPs of 14.2-26 kDa were partially digested after pepsin treatment. Native page analysis further revealed the presence of a high-molecular weight PP in crude and purified plastein product. The bile acid binding capacity was improved by the plastein reaction. The amount of binding sodium deoxycholate, sodium taurocholate, and sodium cholate were 0.75, 2.0 and 1.87 μmol/100 mg respectively.

Enhancing bioactive peptide release and identification using targeted enzymatic hydrolysis of milk proteins

Milk proteins have been extensively studied for their ability to yield a range of bioactive peptides following enzymatic hydrolysis/digestion. However, many hurdles still exist regarding the widespread utilization of milk protein-derived bioactive peptides as health enhancing agents for humans. These mostly arise from the fact that most milk protein-derived bioactive peptides are not highly potent. In addition, they may be degraded during gastrointestinal digestion and/or have a low intestinal permeability. The targeted release of bioactive peptides during the enzymatic hydrolysis of milk proteins may allow the generation of particularly potent bioactive hydrolysates and peptides. Therefore, the development of milk protein hydrolysates capable of improving human health requires, in the first instance, optimized targeted release of specific bioactive peptides. The targeted hydrolysis of milk proteins has been aided by a range of in silico tools. These include peptide cutters and predictive modeling linking bioactivity to peptide structure [i.e., molecular docking, quantitative structure activity relationship (QSAR)], or hydrolysis parameters [design of experiments (DOE)]. Different targeted enzymatic release strategies employed during the generation of milk protein hydrolysates are reviewed herein and their limitations are outlined. In addition, specific examples are provided to demonstrate how in silico tools may help in the identification and discovery of potent milk protein-derived peptides. It is anticipated that the development of novel strategies employing a range of in silico tools may help in the generation of milk protein hydrolysates containing potent and bioavailable peptides, which in turn may be used to validate their health promoting effects in humans. Graphical abstract The targeted enzymatic hydrolysis of milk proteins may allow the generation of highly potent and bioavailable bioactive peptides.

Response surface methodology applied to the generation of casein hydrolysates with antioxidant and dipeptidyl peptidase IV inhibitory properties

BACKGROUND

Hydrolysis parameters affecting the release of dipeptidyl peptidase IV (DPP-IV) inhibitory and antioxidant peptides from milk proteins have not been extensively studied. Therefore, a multifactorial (i.e. pH, temperature and hydrolysis time) composite design was used to optimise the release of bioactive peptides (BAPs) with DPP-IV inhibitory and antioxidant [oxygen radical absorbance capacity (ORAC)] properties from sodium caseinate.

RESULTS

Fifteen sodium caseinate hydrolysates (H1-H15) were generated with Protamex^TM , a bacillus proteinase activity. Hydrolysis time (1 to 5 h) had the highest influence on both DPP-IV inhibitory properties and ORAC activity (P < 0.05). Alteration of incubation temperature (40 to 60 °C) and pH (6.5 to 8.0) had an effect on the DPP-IV inhibitory properties but not the ORAC activity of the Protamex sodium caseinate hydrolysates. A multi-functional hydrolysate, H12, was identified having DPP-IV inhibitory (actual: 0.82 ± 0.24 vs. predicted optimum: 0.68 mg mL^-1 ) and ORAC (actual: 639 ± 66 vs. predicted optimum: 639 µmol TE g^-1 ) activity of the same order (P > 0.05) as the response surface methodology (RSM) predicted optimum bioactivities.

CONCLUSION

Generation of milk protein hydrolysates through multifactorial design approaches may aid in the optimal enzymatic release of BAPs with serum glucose lowering and antioxidant properties. © 2016 Society of Chemical Industry.

Recent Research in Antihypertensive Activity of Food Protein-derived Hydrolyzates and Peptides

Year to year obesity prevalence, reduced physical activities, bad habits/or stressful lifestyle, and other environmental and physiological impacts lead to increase in diseases such as coronary heart disease, stroke, cancer, diabetes, and hypertension worldwide. Hypertension is considered as one of the most common serious chronic diseases; however, discovery of medications with high efficacy and without side effects for treatment of patients remains a challenge for scientists. Recent trends in functional foods have evidenced that food bioactive proteins play a major role in the concepts of illness and curing; therefore, nutritionists, biomedical scientists, and food scientists are working together to develop improved systems for the discovery of peptides with increased potency and therapeutic benefits. This review presents a recent research carried out to date for the purpose of isolation and identification of bioactive hydrolyzates and peptides with angiotensin I converting enzyme inhibitory activity and antihypertensive effect from animal, marine, microbial, and plant food proteins. Effects of food processing and hydrolyzation conditions as well as some other impacts on formation, activity, and stability of these hydrolyzates and peptides are also presented.

Mechanisms of plastein formation, and prospective food and nutraceutical applications of the peptide aggregates

Plastein is a protease-induced peptide aggregate with prospective application in enhancing the nutritional quality of proteins and debittering protein hydrolysates. These properties are yet to be applied in product development possibly due to economic considerations (production cost vs. product yields). This paper reviews currently proposed mechanisms of plastein formation including condensation, transpeptidation and physical interaction of aggregating peptides. Emerging findings indicate that plastein possesses bioactivities, thereby expanding its prospective application. The role of proteases in inducing peptide interaction in plastein remains unclear. Understanding the protease function will facilitate the development of efficient proteases and scalable industrial processes for plastein production.

A virtual screening method for inhibitory peptides of Angiotensin I-converting enzyme

Natural small peptides from foods have been proven to be efficient inhibitors of Angiotensin I-converting enzyme (ACE) for the regulation of blood pressure. The traditional ACE inhibitory peptides screening method is both time consuming and money costing, to the contrary, virtual screening method by computation can break these limitations. We establish a virtual screening method to obtain ACE inhibitory peptides with the help of Libdock module of Discovery Studio 3.5 software. A significant relationship between Libdock score and experimental IC(50) was found, Libdock score = 10.063 log(1/IC(50)) + 68.08 (R(2) = 0.62). The credibility of the relationship was confirmed by testing the coincidence of the estimated log(1/IC(50)) and measured log(1/IC(50)) (IC(50) is 50% inhibitory concentration toward ACE, in μmol/L) of 5 synthetic ACE inhibitory peptides, which was virtual hydrolyzed and screened from a kind of seafood, Phascolosoma esculenta. Accordingly, Libdock method is a valid IC(50) estimation tool and virtual screening method for small ACE inhibitory peptides.

Revisiting the prospects of plastein: thermal and simulated gastric stability in relation to the antioxidative capacity of casein plastein

Plastein, a product of protease-induced peptide aggregation, is thought to possess unique physical properties and bioactivity, although its formation, stability, and functional mechanisms remain unclear. This study demonstrates that plastein is formed from bovine casein peptides with Alcalase by hydrophobic and electrostatic interactions and less likely by covalent bonding. The peptide aggregation enhanced the Fe(III) reducing potential and decreased the Fe(II) chelating activity (p < 0.05) of casein peptides, but there was no difference in inhibition of Fe-induced linoleic acid peroxidation after plastein reaction. The casein plastein product retained its antioxidative activities after being heated at 100 °C. However, simulated gastric protease treatment with pepsin and pancreatic enzymes resulted in enhanced reducing potential and metal chelation of the casein plastein and reduction of the inhibitory effect on lipid peroxidation. It appears that the plasteins were disintegrated and further hydrolyzed by gastric proteases on the basis of the antioxidative capacity and RP-HPLC profile being similar to those of the casein hydrolysates. Therefore, plastein reaction may not confer metabolic stability or enhance the antioxidative capacity of casein peptides for prospective functional food applications.

Increase in antioxidant and antihypertensive peptides from Argentinean wines by Oenococcus oeni

Cells from an exponential Oenococcus oeni m1 culture in a grape juice medium were inoculated into a synthetic wine medium (SW) supplemented with a protein and polypeptide fraction (PPF) of high molecular weight (higher than 12,400 Da) obtained from four varietals of Cafayate Argentinean wines. O. oeni maintains viability after 48 h incubation time and enables the increase in extracellular proteolytic activity and the release of low molecular weight peptides by 1.067, 0.397, 0.915 and 0.705 mg N/L in the respective SW supplemented with PPF from Cabernet Sauvignon, Malbec, Tannat and Torrontés wine varietals. After 48 h incubation time, concomitantly with peptide release, an increase in antioxidant and antihypertensive activities was detected in all studied media. The highest increase was detected in the presence of PPF from Cabernet and Tannat wine varietals. Maximum increase in antioxidant activity (366.1 μmol FeSO4/L in the case of ferric reducing antioxidant power and 8.9% in 2,2-diphenyl-1-picrylhydrazyl radical scavenging) was produced by the peptides released from PPF of Cabernet Sauvignon wine. The peptides released from PPF Tannat wine varietal caused the highest increase in antihypertensive activity (56.2% in angiotensin I-converting enzyme inhibitory activity). Oenococcus oeni m1 would provide additional benefits to wine such as an increase in bioactive peptides with multifunctional beneficial activities.

Optimization of some conditions of Neutrase-catalyzed plastein reaction to mediate ACE-inhibitory activity in vitro of casein hydrolysate prepared by Neutrase

Casein hydrolysate was prepared by hydrolyzing casein with Neutrase and then modified by a Neutrase-catalyzed plastein reaction. The prepared hydrolysate had a degree of hydrolysis of 13.0% and exhibited ACE inhibition in vitro with an IC50 value of 40.4 μg⋅mL(-1). With the decreased amount of free amino groups of the modified hydrolysate as the response, some conditions of the plastein reaction including substrate concentration, enzyme to substrate ratio, reaction temperature and time were studied by single factor experiments and response surface methodology, and optimized finally as 62% (w/w), 3.0 kU⋅g(-1) peptides, 30 °C and 6.3 h, respectively. The maximum decreased amount of free amino groups of the modified hydrolysate prepared under these optimized conditions was 210.0 μmol⋅g(-1) peptides, while corresponding IC50 value was lowered to 14.7 μg⋅mL(-1). The present result indicates that Neutrase-catalyzed plastein reaction was capable of enhancing ACE-inhibitory activity in vitro of casein hydrolysate, and also highlights the importance of a forthcoming study to investigate the peptide compositions of the modified hydrolysate and the role of protease used in the plastein reaction.