Separation and identification of ACE inhibitory peptides from defatted walnut meal

Effect of Alkyl Peroxyl Radical Oxidation on the Oxidative Stability of Walnut Protein Emulsions and Their Adsorbed Proteins

Walnuts are high in protein content and rich in nutrients and are susceptible to oxidation during production and processing, leading to a decrease in the stability of walnut protein emulsions. In this paper, the effect of alkyl peroxyl radical oxidation on the stability of walnut protein emulsions is investigated. With the increase of 2,2-azobis (2-methylpropionamidine) dihydrochloride (AAPH) concentration, both its protein and fat were oxidized to different degrees, and the droplets of the emulsion were first dispersed and then aggregated as seen from the laser confocal, and the stability of walnut protein emulsion was best at the AAPH concentration of 0.2 mmol/L. In addition to this, the adsorption rate of adsorbed proteins showed a decreasing and then an increasing trend with the increase in the oxidized concentration. The results showed that moderate oxidation (AAPH concentration: 0-0.2 mmol/L) promoted an increase in protein flexibility and a decrease in the protein interfacial tension, leading to the decrease in emulsion droplet size and the increase of walnut protein emulsion stability, and excessive oxidation (AAPH concentration: 1-25 mmmol/L) weakened protein flexibility and electrostatic repulsion, making the walnut protein emulsion less stable. The results of this study provide theoretical references for the quality control of walnut protein emulsions.

Isolation and identification of angiotensin-converting enzyme inhibitory peptides from Tartary buckwheat albumin

BACKGROUND

Tartary buckwheat protein peptides have been shown to be able to inhibit angiotensin-converting enzyme (ACE), but the exact protein type has been less studied for ACE activity inhibition, and only a few types of ACE inhibitory peptides have been reported. In this study, we purified and identified ACE inhibitory peptides from albumin hydrolysate (AH).

RESULTS

Albumin, globulin, prolamin and glutelin were extracted from Tartary buckwheat, and their ACE active peptides were obtained by a pepsin-trypsin sequential hydrolysis process. All four hydrolysates exhibited ACE inhibitory activity, and AH displayed the strongest ACE inhibition activity and the highest peptide yield (82.28%). At 0.2 mg mL^-1 , the inhibition rate of AH was 79.89%, followed by globulin hydrolysate at 71.84%, while prolamin hydrolysate and glutelin hydrolysate showed lower inhibition rates. The peptides with the highest inhibition rate were then isolated from AH using gel filtration chromatography and reversed-phase high-performance liquid chromatography, and identified using nanoscale high-performance liquid chromatography-tandem mass spectrometry. After isolation and purification, 42 ACE inhibitory peptides were identified in the fraction with the highest inhibition rate, 14 of which were completely novel discoveries in this study. These 14 peptides showed potent ACE inhibitory effects through computer analysis.

CONCLUSION

Tartary buckwheat albumin can be used as a good source of ACE inhibitory peptides and can be further developed and utilized as edible supplements or drugs. © 2023 Society of Chemical Industry.

Effect of Oxidative Modification by Peroxyl Radical on the Characterization and Identification of Oxidative Aggregates and In Vitro Digestion Products of Walnut (Juglans regia L.) Protein Isolates

Walnut protein is a key plant protein resource due to its high nutritional value, but walnuts are prone to oxidation during storage and processing. This article explored the oxidative modification and digestion mechanism of walnut protein isolates by peroxyl radical and obtained new findings. SDS-PAGE and spectral analysis were used to identify structural changes in the protein after oxidative modification, and LC-MS/MS was used to identify the digestion products. The findings demonstrated that as the AAPH concentration increased, protein carbonyl content increased from 2.36 to 5.12 nmol/mg, while free sulfhydryl content, free amino content, and surface hydrophobicity decreased from 4.30 nmol/mg, 1.47 μmol/mg, and 167.92 to 1.72 nmol/mg, 1.13 μmol/mg, and 40.93 nmol/mg, respectively. Furthermore, the result of Tricine-SDS-PAGE in vitro digestion revealed that protein oxidation could cause gastric digestion resistance and a tendency for intestinal digestion promotion. Carbonyl content increased dramatically during the early stages of gastric digestion and again after 90 min of intestine digestion, and LC-MS/MS identified the last digestive products of the stomach and intestine as essential seed storage proteins. Oxidation causes walnut proteins to form aggregates, which are then re-oxidized during digestion, and proper oxidative modification may benefit intestinal digestion.

A multi-functional survey of the properties of Lacticaseibacillus paracasei subsp. tolerans NOC-122, Levilactobacillus parabrevis NOC-111 and Latilactobacillus curvatus NOC-110

This study aimed to reveal the physicochemical and organoleptic effects of three functional lactic acid bacteria (LAB) isolates in a milk medium: Lacticaseibacillus paracasei subsp. tolerans NOC-122, Levilactobacillus parabrevis NOC-111 and Latilactobacillus curvatus NOC-110. A total of 200 indigenous LAB strains isolated from artisanal tulum cheeses were screened for potential proteolytic and lipolytic activity, citrate-lyase-synthesizing and exopolysaccharide-producing ability. Furthermore, a total of six fermented products were produced using these strains as a single culture or as a co-culture. The physicochemical and microbiological properties, angiotensin-converting-enzyme (ACE) inhibitor activity, and the amino acid and volatile aroma compound profiles were determined. According to the results, NOC-110 and NOC-122 were effective in increasing ACE-inhibitory activity. On the other hand, NOC-122 was responsible for a fresh cheesy, slightly oily flavour when used as a single culture. NOC-111 gave a fresh, fruity and slightly herbal flavour; NOC-110 gave a flavour similar to that of NOC-122 when they were used as a single culture. Also, co-cultures of the strains were investigated. The results of the study provide a guide to the usability of these isolates as single or co-cultures in the production of dairy-based food. These findings can be of value for many future studies and innovative food products.

Antihypertensive effects of abalone viscera fermented with Lactiplantibacillus pentosus SN001 via angiotensin-converting enzyme inhibition

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L. pentosus SN001-fermented abalone viscera reduced blood pressure in vivo.

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L. pentosus SN001-fermented abalone viscera did not affect rat blood composition.

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L. pentosus SN001-fermented abalone viscera had a good safety profile.

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Uracil was identified from L. pentosus SN001-fermented abalone viscera.

Abalone viscera, which accounts for more than 20% of body weight, is typically discarded. With increases in abalone aquaculture production, novel uses for abalone viscera are needed. Here, we evaluated the effects of abalone viscera fermented with Lactiplantibacillus pentosus SN001 on angiotensin-converting enzyme (ACE) activity and blood pressure elevation in spontaneously hypertensive rats. The fermented product significantly reduced systolic blood pressure compared with the control. There were no significant differences in blood glucose, triglyceride, total cholesterol, or high-density lipoprotein cholesterol levels; alanine aminotransferase activity; and aspartate aminotransferase activity between the fermented product and control groups. Uracil was isolated and identified from the fermented product. Uracil may be the active component. Overall, L. pentosus SN001-fermented abalone viscera showed sustained inhibitory effects on blood pressure elevation but did not alter blood components after long-term intake. These results provide insights into the safety of L. pentosus SN001-fermented abalone viscera as a food product.

Identification of in vitro angiotensin-converting enzyme and dipeptidyl peptidase IV inhibitory peptides from draft beer by virtual screening and molecular docking

BACKGROUND

Hypertension and diabetes are two kinds of senile diseases which often occur simultaneously. The commonly used drugs in clinic may produce certain side effects. Food-derived polypeptide is a kind of polypeptide with great development potential, which has many functions of regulating human physiological function. Beer is rich in nutrition but there are few researches on bioactive peptides in beer.

RESULTS

In this study, a rapid virtual screening method was established to obtain bioactive peptides from Tsingtao draft beer. The peptide sequence was analyzed by ultra-performance liquid chromatography-quadrupole-Orbitrap-tandem mass spectrometry (UPLC-Q-Orbitrap-MS² ), and 50 peptides were identified. Eight peptides with potential biological activities were screened by using Peptide Ranker software and previous literature references. On the basis of absorption prediction, toxicity prediction, and molecular docking analysis, LNFDPNR and LPQQQAQFK were finally confirmed. The molecular docking results showed that two peptides could bind angiotensin-converting enzyme (ACE) and dipeptidyl peptidase IV (DPP-IV) tightly by hydrogen bonding and hydrophobic interaction. The in vitro activity evaluation results showed that two peptides had obvious ACE and DPP-IV inhibitory activity.

CONCLUSION

This study established a method for rapidly screening bioactive peptides from Tsingtao draft beer, screened two ACE and DPP-IV inhibitory peptides in beer and analyzed their active action mechanism. This article may have great theoretical significance and practical value to further explore the health function of beer. © 2021 Society of Chemical Industry.

The efficient enrichment of marine peptides from the protein hydrolysate of the marine worm Urechis unicinctus by using mesoporous materials MCM-41, SBA-15 and CMK-3

Peptides found in marine life have various specific activities due to their special growth environment, and there is increasing interest in the isolation and concentration of these biofunctional compounds. In this study, the protein hydrolysate of the marine worm Urechis unicinctus was prepared by enzymolysis and enriched by using mesoporous materials of silica MCM-41 and SBA-15 and carbon CMK-3. The differences in pore structures and elemental composition of these materials lead to differences in surface area and hydrophobicity. The adsorption capacities of peptides were 459.5 mg g^-1, 431.3 mg g^-1, and 626.3 mg g^-1 for MCM-41, SBA-15 and CMK-3, respectively. Adsorption kinetics studies showed that the pseudo-second-order model fit the adsorption process better, where both external mass transfer and intraparticle diffusion affected the adsorption, while the Langmuir model better fit the adsorption of peptides on MCM-41 and SBA-15 and the Freundlich model was more suitable for CMK-3. Aqueous acetonitrile (ACN, 50/50, v/v) yielded the most extracted peptides. MALDI-TOF mass spectrometry of the extracted peptides showed that the three mesoporous materials, especially the CMK-3, gave good enrichment results. This study demonstrates the great potential of mesoporous materials in the enrichment of marine biofunctional peptides.

Protective effect against d-gal-induced aging mice and components of polypeptides and polyphenols in defatted walnut kernel during simulated gastrointestinal digestion

Defatted walnut kernel with pellicle (WKP) is an industrial byproduct during walnut oil extraction, which is rich in protein and polyphenols. WKP was hydrolyzed by simulated gastrointestinal digestion to obtain WKP hydrolysates (WKPHs). Results showed the protein recovery and hydrolysis degree of WKPH were 82.15 and 10.36%. The total phenol contents in WKP and WKPH were 4.90 and 40.70 mg gallic acid equivalent/g, respectively. The antiaging activity of WKPH was evaluated using a d-gal-induced aging mouse model. Results showed that WKPHs could recover the activities of SOD and T-AOC and the content of MDA in tissues and serum of the aging mice. The histological morphology of liver and kidney sections and the immunohistochemistry of TNF-α, IL-1β, and IL-6 in liver were observed. WKPH could effectively protect the tissue structure of the liver and kidney and reduce the inflammatory expression of liver in aging mice. The polypeptides and polyphenols in WKPH were further analyzed. Fifty polypeptides were identified and 12 of these peptides had Leu-Arg at the C-terminal. Forty-two polyphenols were detected, and most phenolic compounds belonged to ellagitannins. This study provided a theoretical basis for the improved processing and high-value utilization of walnut byproducts. PRACTICAL APPLICATION: Defatted walnut kernel with pellicle was hydrolyzed by simulated gastrointestinal digestion to obtain its hydrolysates. The hydrolysates have good antiaging activity in vivo. Fifty polypeptides were identified and 12 of these peptides had Leu-Arg at the C-terminal. Forty-two polyphenols were detected, and most phenolic compounds belonged to ellagitannins. This study could provide a theoretical basis for high-value utilization of walnut byproducts.