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Milk protein concentrate was hydrolyzed using one-step enzymatic hydrolysis. Both the peptide profiles and antioxidant activities of the resulting extensive hydrolysates of milk protein concentrate (EMPH) were analyzed using a peptidomics approach based on liquid chromatography-tandem mass spectrometry. The results demonstrated that the degrees of hydrolysis of the 4 EMPH by Alcalase-Protamex, Alcalase-Protease A 2SD, Alcalase-Flavorzyme, and Alcalase-ProteAXH were 12.02%, 16.85%, 15.87%, and 15.77%, respectively. Using size exclusion chromatography, 99.85% of the peptides in the Alcalase-Protease A 2SD hydrolysate were shown to have a molecular weight of <3 kDa. A total of 33 common peptides were identified in the EMPH by liquid chromatography-tandem mass spectrometry, 16 of which were identified as bioactive peptides using bioinformatics. The peptide profiles and the coverage of master proteins of the 4 EMPH were different. The EMPH also exhibited strong free radical scavenging capacity, as indicated by the results of the 1,1-diphenyl-2-picrylhydrazyl radical, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), hydroxyl radical, and reducing power assays. The results of this study provided useful information on the peptide profiles and antioxidant activity of EMPH., (The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Watermelon seed, a watermelon processing industry by-product, is a good protein source for the preparation of antioxidant peptides due to its high protein content, low cost, special amino acid composition. Antioxidant hydrolysates obtained from watermelon seed protein (WSP) after slit divergent ultrasound (SDU) treatment were studied. The stepwise multiple linear regression model verified that the reducing power of watermelon seed protein hydrolysates (WSPHs) is positively related with -SH and β-turn content of WSP (R 2  = 0.931, p < 0.01). Using the degree of hydrolysis (DH) and reducing power as indicators, the WSPHs was prepared under the optimal conditions (ultrasound frequency: 20/28 kHz, time: 60 min, power density: 100 W/L) and divided into three components by ultrafiltration membrane (1 and 5 kDa). Compared with WSPHs and other fractions, WSPHs-I (Mw < 1 kDa) not only significantly protected HepG2 cells from H 2 O 2 -induced damage, but also greatly alleviated the liver injury caused by d-galactose in male SD rats., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The aim of this study was to purify and identify antioxidant peptides from watermelon seed protein hydrolysates (WSPHs-I: Mw < 1 kDa) and further evaluate their cytoprotective effects against H 2 O 2 -induced oxidative stress in HepG2 cells. After purification by Sephadex G-15 and semi-preparative reversed-phase high performance liquid chromatography (RP-HPLC), five peptides, RDPEER (P1), KELEEK (P2), DAAGRLQE (P3), LDDDGRL (P4), and GFAGDDAPRA (P5) were sequenced by LC-MS/MS and synthesized with solid-phase synthesis method. These peptides showed desirable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity (IC 50 : 0.216 ± 0.01-0.435 ± 0.03), 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging capacity (IC 50 : 0.54 ± 0.02-1.23 ± 0.03), and oxygen radical absorbance capacity (ORAC) (82.36 ± 1.2-130.67 ± 2.2 μM TE/mg). Among them, peptide P1 exhibited the strongest antioxidant capacity. Moreover, the results suggested that peptide P1 may protect HepG2 cells from H 2 O 2 -induced oxidative damage by significantly inhibiting reactive oxygen species (ROS), [Ca 2+ ]i, malondialdehyde (MDA) levels and increasing antioxidative enzyme activities., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Effects of multi-frequency S-type ultrasound (MFSU) assisted arrowhead protein (AP) hydrolysis on the antioxidant activity of its hydrolysates were studied. The results showed the DPPH • and ABTS•+ scavenging activity of hydrolysates obtained with dual frequency ultrasound (20/40 kHz) was 63.61% and 65.11%, respectively, and was higher than that noted for hydrolysates acquired with assistance of other mode (single and triple frequency ultrasound). Compared with hydrolysates without ultrasonic treatment, products of AP hydrolysis assisted by dual frequency ultrasound (20/40 kHz) could significantly alleviate oxidative stress induced by H 2 O 2 in RAW 264.7 cells, mainly embodied in improving the survival rate and increasing the activity of antioxidant enzymes (CAT and SOD). Taken together, these results showed that MFSU-assisted enzymatic treatment can significantly improve the antioxidant activity of AP hydrolysates. Thus, the development of the novel MFSU could lay a foundation for assisting the protein enzymolysis in food and pharmaceutical industries.

In this study, separation of peptides with Angiotensin I converting enzyme (ACE)-inhibitory capacity obtained from ultrasonically pretreated defatted corn germ protein (DCGP) by using a new continuous system of enzymatic hydrolysis coupled with membrane separation (EHC-MS) was investigated. Ultrasonic pretreatment was applied to enhance the enzymatic hydrolysis rate of DCGP, as proved in our previous study. The EHC-MS system was operated in two modes which included the batch system and continuous system with continuous water and substrate feeding and was compared with the EH-offline-MS system. The selection of the membrane was based on the hydrolysate fraction which had the highest activity for inhibition of ACE. The results showed that the 1-3 kDa fraction of DCGP hydrolysates had the lowest IC50 value (0.124 mg mL-1) for inhibition of ACE. The degree of conversion (%) of DCGP and output of peptides per unit of the enzyme were significantly (P < 0.05) increased by 55.3% and 55% in the EHC-MS batch process and 79% and 473% in the EHC-MS continuous operation compared to the EH-offline-MS system. The EHC-MS using continuous water and substrate feeding operation was noted to be the best in terms of a high degree of DCG protein conversion (75.68 ± 1.34) and the output of peptides per unit of the enzyme (78.65 ± 1.13). The results revealed that the EHC-MS method with constant water and substrate feeding could show a better application in peptide production in the food industry.

There is a growing demand in reusing agro-industrial waste to enrich food proteins and develop new protein-related products. Brewer's spent grain (BSG), the byproducts generated from the processing of beer-brewing industry, is rich in abundant protein (26 to 30%) with good physicochemical properties and nutritional benefits. BSG is mainly composed of four proteins including hordein, gluten, globulin, and albumin. The methods for extracting protein from BSG mainly include alkali extraction, ultrasonic-assisted extraction, and organic solvent extraction, among others. However, little researches have described the functional properties of Brewer's spent grain protein (BSGP) and how it can be improved by enzymatic modification. Additionally, BSG protein hydrolysates (BSGPHs) have good bioactivities, mainly including antioxidant, antiinflammatory, and angiotensin-I-converting enzyme inhibitory activities, among others. Based on the above situation, this review provides a comprehensive overview about the isolation, physicochemical features, application of the BSGP. In addition, the functional properties and biological activities of BSGPHs are also emphasized. The purpose of this review is to provide an up-to-date summary of BSGP research, and to broaden the market potential of this emerging protein in food industry. Besides, this review provides a reference to study the use of BSGP or hydrolysates for a variety of purposes in-depth, including pharmaceutical, food, and industrial applications., (© 2019 Institute of Food Technologists®.)

In the present study, the antioxidant hydrolysates obtained from watermelon seed protein (WSP) after divergent ultrasound and ultrafiltration treatment were studied. The results showed that the slit divergent ultrasound (SDU, 20/28 KHz) pretreatment had considerable influence on the structure and enzymatic efficiency of WSP. Besides, compared with hydrolysates without ultrasonic and ultrafiltration treatment, watermelon protein hydrolysates with molecular weight <1 kDa (WSPHs-I) showed the highest antioxidant activities and could protect RAW 264.7 cells from H 2 O 2 -induced oxidative stress damage via activating the Nrf2/HO-1 pathway. Interestingly, WSPHs-I had good stability against oxidation at temperature under 100 °C or in the acidic or neutral condition and still exhibited strong antioxidant activity after simulated gastrointestinal digestion. Taken together, SDU pretreatment could significantly increase the antioxidant activities and stability of WSPHs by improving the structure and facilitating enzymolysis of the WSP., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Background : Dietary proteins are known for their wide range of nutritional, functional and biological properties. Although the total amount of proteins may be obtained from mixtures, its "availability" for absorption in the gut is in many cases quite uncertain or even varies for the same food depending on processing conditions, the presence of other components, and so on. Methods : To obtain accurate protein hydrolysate absorption data, we have developed a small intestine model (SIM) to test them. Results : The results indicated that the protein hydrolysates were absorbed rapidly during the first 15 min, and then decreased to 90 min, then they were absorbed again from 90 min to the endpoint. The protein absorption was also affected by the protein processing method used. The Enzyme + Ultrasound (EU) processing method group had a higher absorption rate than the Enzyme (E) processing method group, and the absorption of the Enzyme + Artificial gastric juice processing method (EH) and Enzyme + Ultrasound + Artificial gastric juice processing method (EUH) groups was reduced compared to the E group alone. The amino acid analysis results showed that the amino acids were reduced and absorbed by our SIM in almost all groups except for cysteine and methionine. In general, the Pearson relation value of the amino acid contents between before SIM and after SIM was 0.887, which indicated that single amino acid absorption was mainly related to its content in the whole amino acids. The single amino acid absorption ratio among different groups also displayed differences, which ranged from 31% to 46% (E group from 39% to 42%; EU group from 40% to 47%; EH group from 31% to 39%; EUH group from 35% to 41%)., Conclusions: The protein hydrolysates' varied from startpoint to endpoint, and the protein absorption was affected by processing method., Competing Interests: The authors declare no conflict of interest.

In recent years, the antioxidant capacity of plant protein-derived peptides has been depicted in a growing number of studies. Plant proteins have been considered as the new source of antioxidant peptides, which not only save energy but also strengthen treatment of oxidation-related diseases and delay the oxidation of food, thus improve the quality of life. Although reports of the preparation, structure, and activity of antioxidant peptides has increased tremendously and some antioxidant peptides have been commercialized. However, research on antioxidant peptides derived from plant proteins still lacks a systematic review and evaluation. This review summarizes recent advances in plant protein-derived antioxidant peptides, mainly including: (i) Preparation, purification, identification and application of plant protein-derived antioxidant peptides by enzymatic hydrolysis; (ii) Influencing factors, evaluation methods and mechanism of antioxidant protein hydrolysates or peptides; (iii) Future research prospects and existing problems. The conventional purification and identification of antioxidant peptides are expensive and time-consuming. In order to overcome this problem, computer-aided mathematical models (molecular docking, QSAR research, etc.), bioinformatics tools and real-time updated protein databases have been widely explored and studied. In addition, future research should focus on large-scale commercial production of plant protein-derived antioxidant peptides, comprehensive study of structure-activity relationship of antioxidant peptides, deep understanding of antioxidant mechanism, and verification of health benefits in viv o. This review provides a timely reference for the development of new antioxidant peptides in functional foods and nutritional supplements. • Plant proteins as sources of antioxidant peptides were reviewed. • Antioxidant peptides by enzymatic hydrolysis were prepared in past 20 years. • Antioxidant peptides can be predicted using computation-aided mathematical models. • Analytical methods to evaluate activities of antioxidant peptides were reviewed. • Antioxidant mechanisms of the peptides were discussed. [ABSTRACT FROM AUTHOR]

• The ultrasound pretreatment enhanced the enzymatic hydrolysis of defatted corn germ protein. • The enzymatic hydrolysis kinetics followed the First-order kinetic model. • The ultrasound pretreatments of defatted corn germ protein reduced the thermodynamic parameters. In this paper, the impact of ultrasound pretreatment on the kinetics and thermodynamics of defatted corn germ protein (DCGP) enzymatic hydrolysis was evaluated. The enzymatic hydrolysis kinetics and thermodynamics were studied for traditional method and ultrasonic pretreatments with a single-frequency counter-current S type (20 KHz) (SFU) and a multi-frequency counter-current S type (20, 28, 35 and 40 KHz) (MFU). The results showed that the traditional, SFU and MFU pretreated enzymatic hydrolysis of DCGP followed the First-order kinetic model. Again, the SFU and MFU pretreatments enhanced the enzymatic hydrolysis of DCGP. Compared to traditional enzymatic hydrolysis, the reaction rate constant values were increased by 50.0%, 54.7%, 47.8% and 52.3% for SFU pretreated enzymatic hydrolysis, and 58.0%, 58.5, 53.6% and 54.7% for MFU pretreated enzymatic hydrolysis at 20, 30, 40 and 50 ºC respectively. Also, the results showed that the SFU and MFU ultrasound pretreatments of DCGP reduced the thermodynamic parameters which included the activation energy (Ea), enthalpy (ΔH), entropies (ΔS) and Gibbs free energy (ΔG) in enzymatic hydrolysis reaction. [ABSTRACT FROM AUTHOR]