Antioxidant Activity Of Hydrolysates Research Articles

Protein hydrolysates from Mytilus edulis L. mussel: Physicochemical and antioxidant properties

Meat of marine molluscs is a promising protein-containing raw material for obtaining protein hydrolysate and biologically active peptides. The purpose of this research was to study the physicochemical properties and antioxidant properties of protein hydrolysate obtained from the mussel Mytilus edulis L. The hydrolysates were obtained by acidic hydrolysis and enzymatic hydrolysis using protozyme as an enzyme. Gel permeation chromatography was used as experimental method in this study to characterise the molecular weight distribution of the protein hydrolysates. Chemical analysis was used for determine the composition and antioxidant activity of hydrolysates. It is shown that the content of low-molecular fractions - biologically active peptides with a molecular weight of less than 5 kDa is almost three times higher in the enzymatic hydrolysate compared to the acidic one. Accordingly, the enzymatic hydrolysate demonstrates high antioxidant activity, which determines its prospects as a component for functional food products and biomedical drugs.

Structural changes induced by ultrasound in proteases and their consequences on the hydrolysis of pumpkin seed proteins and the multifunctional properties of hydrolysates

The effects of ultrasound (US) (40 kHz, 23.8 W/L) on commercial protease structures and their impact on pumpkin seed protein (PSP) hydrolysis were evaluated, as well as the solubility and antioxidant activity of hydrolysates. The ultrasonic pre-treatment activated Neutrase® (22.7 %), Brauzyn® (20.8 %) and Flavourzyme® (22.4 %), with more significant changes in the tertiary structure of Flavourzyme®, which also showed the highest increases in particle size (∼21 %) and polydispersity index (PDI) (∼60 %) compared to its native form. On the other hand, US pre-treatment under inactivation conditions resulted in substantial structural changes, indicating protein denaturation with the formation of heterogeneous and strongly electronegative aggregates. Proteolysis of PSP with US-activated enzymes showed a higher degree of hydrolysis (DH) (up to 75 %) and the obtained peptides showed higher solubility (up to 53 %) and antioxidant activity (up to 40 %). The findings emphasize that applying ultrasound under specific conditions can induce moderate structural changes in proteases, enhancing their hydrolytic efficiency.

Physicochemical, antioxidant, antimicrobial, and in vitro cytotoxic activities of corn pollen protein hydrolysates obtained by different peptidases.

The applications of protein hydrolysates as food preservatives and nutraceutical ingredients have attracted much attention because of their beneficial effects. The interest in these ingredients has shifted toward their biological activities with benefits to human health. Bioactive peptides are known as antioxidant agents that could promote health-promoting effects and prolong food shelf-life beyond their basic nutritional value. Thus, the aim of this study was to investigate antioxidant, antimicrobial, and in vitro cytotoxic properties of corn pollen protein (CPP) hydrolysates obtained by different enzymes. Proteolytic activity in terms of degree of hydrolysis (DH) and SDS-PAGE analysis was measured in pancreatin (H-Pan), pepsin (H-Pep), and trypsin (H-Tri) hydrolysates. Amino acid composition, antioxidant and antimicrobial activities, and cytotoxicity of hydrolysates were evaluated. DH and SDS-PAGE revealed higher proteolytic activity of pepsin compared to other enzymes. Amino acid analysis showed that the functional amino acids such as antioxidant types were most predominant in H-Pep compared to two other samples. Antioxidant activity of hydrolysates was found to be affected by the type of enzyme and the concentration of hydrolysates. There was a significant difference (p < 0.05) between antioxidant activity of different hydrolysates. The highest antioxidant activity in terms of Trolox equivalent antioxidant capacity (0.23-2.75 mM), DPPH (33.3%-64.8%), and hydroxyl (33.7%-63.2%) radical scavenging activities, chelation of iron (33.2%-62.5%) and copper (30.2%-50.5%) metals, and total antioxidant activity (0.65-0.85) was obtained for H-Pep followed by H-Pan and H-Tri samples. Antibacterial tests showed that pepsin-hydrolyzed protein was not significantly (P > 0.05) effective against E.coli at any concentrations, however, it showed significant (P < 0.05) concentration-dependent effect against S.aureus (with inhibition zones of 15-25 mm). Cytotoxicity results revealed that CPP, as a nonhydrolyzed protein, did not generally show antiproliferative activity, however, a significant (P < 0.05) ability of H-Pep hydrolysate in decreasing HT-29 colon cancer cell line viability was seen in a concentration-dependent manner (the lowest cell viability of 32% at 5mg/mL). Overall, investigating the application of protein-based hydrolysates is one of the possible strategies that govern their applied intentions as preservatives and nutraceuticals in the food and pharmaceutical industries.

Effects of High-Pressure Treatments (Ultra-High Hydrostatic Pressure and High-Pressure Homogenization) on Bighead Carp (Aristichthys nobilis) Myofibrillar Protein Native State and Its Hydrolysate

The impacts of four treatments, ultra-high hydrostatic pressure (UHP), high-pressure homogenization (HPH), combined UHP + HPH (U-H), and HPH + UHP (H-U), on bighead carp (Aristichthys nobilis) myofibrillar protein (BMP) structure, functional hydrolysis property to pepsin, and antioxidant activity of hydrolysates were investigated. All treatments led to increase in low-molecular-weight BMP, the BMP stability, and hydrophobic group exposure, but decrease in total sulfhydryl content and BMP particle size, thus resulting in increased hydrolysis and antioxidant capacity of enzymatic hydrolysates. U-H treated BMP exhibited the highest surface hydrophobicity (924.5 ± 1.0), zeta potential absolute value (18.88 ± 0.11 mV), hydrolysis degree (54.5 ± 1.6%), and antioxidant activity, but the lowest α-helix (21.84 ± 2.61%), intrinsic fluorescence spectrum intensity, total sulfhydryl (7.24 ± 0.07 μmol/g), and mean particle size (182.57 ± 2.23 nm). Therefore, U-H might be a promising pretreatment to prepare bioactive peptide.

Ultrasound-assisted enzymatic hydrolysis of goat milk casein: Effects on hydrolysis kinetics and on the solubility and antioxidant activity of hydrolysates

This study evaluated the ability of ultrasound (US) bath to improve the hydrolysis of goat milk casein (GMC) by three commercial proteases (Alcalase, Brauzyn and Flavourzyme) using assisted reactions at 60 °C for up to 300 min. Process performance was evaluated based on the rate reaction, final hydrolysis degree, solubility, and antioxidant activity of the hydrolysates. For all enzymes, the US-assisted reaction increased the rate of GMC hydrolysis (up to 120%), the hydrolysis degree (23–48%), and the small peptides formed, i.e., those soluble in trichloroacetic acid (TCA) (up to 40%). Consequently, US-assisted GMC hydrolysis improved the solubility of the hydrolyzed product (up to a 35.7% increase after 300 min of reaction) and, compared to conventional hydrolysis, reduced the time to achieve the maximum solubility by up to 10 times. Regarding the in vitro antioxidant activity, especially for Alcalase, the technology promoted a higher scavenging capacity of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) (p < 0.05), thus 10-fold accelerating the production of antioxidant peptides, according to ABTS assays (p < 0.05). In conclusion, the US-assisted enzymatic reaction is a promising technology to improve the hydrolysis rate and yield of the process of obtaining hydrolysates from GMC. Moreover, these hydrolysates showed high solubility and good in vitro antioxidant activity, which demonstrates the potential to be used as food ingredient with nutritional and techno-functional appeal.

Improving the enzymolysis efficiency of lupin protein by ultrasound pretreatment: Effect on antihypertensive, antidiabetic and antioxidant activities of the hydrolysates

This study evaluated the impact of ultrasound pretreatment (UP) and enzyme type (flavourzyme, alcalase) on amino acid composition, antihypertensive, antidiabetic, and antioxidant activities of lupin protein hydrolysate (LPH). The UP altered molecular weight of the hydrolysates as revealed by SDS-PAGE and MALDI-TOF and their surface hydrophobicity and thermal stability. Amino acid analysis revealed that glutamic acid, aspartic acid, arginine, and leucine were the dominant amino acids lupin protein. Generally, sonicated hydrolysates exhibited higher biological activity than non-sonicated samples and the original LPI. Alcalase hydrolysate pretreated for 10 min showed the highest DPPH and metal chelating activities. Highest ACE inhibitory activity was observed in flavourzyme hydrolysate after 5 min of UP, while maximum α-amylase and glucosidase inhibitory activity was achieved after 10 min of UP in flavourzyme hydrolysate. The results obtained in this study demonstrated the potentials of UP as a valuable tool for enhancing the biological activity of lupin proteins.

Enhancing emulsion stability: The synergistic effect of combining Procream and partially hydrolyzed whey protein

Whey protein concentrate (WPC) was hydrolyzed by trypsin and Protease M from Aspergillus oryzae. Structure and functionality of WPC, hydrolysates, and a whey co-product, Procream, were evaluated for their impact on emulsion stability. Emulsification properties and antioxidant activity of hydrolysates were uniquely impacted by the type of enzyme and the degree of hydrolysis. The physical stability of the emulsions, assessed by turbidity and particle size, and the oxidative stability, assessed by measuring peroxides, were related to physiochemical characteristics. Trypsin hydrolysis significantly decreased surface hydrophobicity, by preferentially targeting β-lactoglobulin, and increased zeta potential, resulting in enhanced water solubility. Hydrolysis improved/maintained emulsification properties and enhanced antioxidant activity. In fish oil emulsions, a synergistic effect on both physical and oxidative stability was observed when combining hydrolysates and Procream. Trypsin hydrolysate + Procream emulsion demonstrated the best oxidative stability. Results demonstrated a successful approach to valorize a whey co-product for targeted emulsion applications.

Autolysis of Pacific white shrimp (Litopenaeus vannamei) processing by-products: Enzymatic activities, lipid and protein oxidation, and antioxidant activity of hydrolysates

Autolysis (at fixed temperatures (FT) or gradually increasing temperatures (GIT) with different times) was studied by measuring enzymatic activities, lipid and protein oxidation, and antioxidant activity of Pacific white shrimp by-product hydrolysates. Trypsin had its highest activity at 40 °C, 2 h and pH 8 (45 mU/mL) followed by 40 °C, 3 h and pH 8 (40 mU/mL) (P ≤ 0.05). The increase in autolysis time and temperature was accompanied by a drop-in enzyme activity and TCA-soluble peptide content (P ≤ 0.05). The peptide fraction with MW < 1000 Da was the main peptide fraction, accounting for 97.0, 98.4, and 96.7% of total peptides in FT-40 (1 h), FT-60 (3 h) and GIT (3 h), respectively. The order of lipid oxidation was FT-60 > GIT > FT-50 > FT-40. FT-50 and FT-60 had the lowest sulfhydryl group content with a coincidental higher protein carbonyl (P ≤ 0.05). The higher temperatures of FT led to a decrease of essential amino acids, especially when autolysis time increased. GIT showed the highest DPPH radical scavenging activity, ferric reducing antioxidant power (FRAP) and metal chelating ability (P ≤ 0.05). Results might be useful to increase the value of Pacific white shrimp by-products for protein hydrolysates production using autolytic hydrolysis technology.

Purification and characterization of antioxidant peptides from yak (Bos grunniens) bone hydrolysates and evaluation of cellular antioxidant activity.

In this study, papain and alcalase were used to generate antioxidant peptides from yak bone protein. The antioxidant activities of hydrolysates in vitro were evaluated by 2,2'-azinobios-(3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging activity, total reducing power, ferrous ion chelating ability and hydroxyl radical scavenging activity. The hydrolysates generated by alcalase possessed the best antioxidant activity among unhydrolyzed protein and samples treated by papain, but the antioxidant activity decreased after simulated gastrointestinal digestion in vitro. The products of simulated gastrointestinal digestion were separated by ultrafiltration and high performance liquid chromatography, and the amino acid sequences of peptides were identified by mass spectrometry. The digestion sites within peptides were predicted by a bioinformatics strategy, and ten peptides were selected for synthesis. Among 10 synthetic peptides, Gly-Phe-Hyp-Gly-Ala-Asp-Gly-Val-Ala, Gly-Gly-Pro-Gln-Gly-Pro-Arg and Gly-Ser-Gln-Gly-Ser-Gln-Gly-Pro-Ala possessed strong antioxidant activities, among which Gly-Phe-Hyp-Gly-Ala-Asp-Gly-Val-Ala had a significant cytoprotective effect in Caco-2 cells under oxidative stress induced by H2O2, which reduced the formation of reactive oxygen species and malondialdehyde, and improved the activity of antioxidant enzymes in cells. These results showed that yak bone peptides exhibited strong antioxidant activity and have a potential value as a new type of natural antioxidant.

Effects of ultrasound and ohmic heating pretreatments on hydrolysis, antioxidant and antibacterial activities of whey protein concentrate and its fractions

Ultrasound and ohmic heating pretreatments may unfold the complex structure of Whey proteins and increase their susceptibility to hydrolysis by proteolytic enzymes. In the present study, Whey protein concentrate (WPC) was hydrolyzed by pepsin after pretreatments with ohmic heating (5 and 15 s), ultrasound (5 and 15 min), and their combinations. We evaluated the pH value, degree of hydrolysis (DH), antioxidant activity of the hydrolysates, HPLC profile, antioxidant, and antibacterial activities of the fractions. The results indicated that the combined pretreatments could significantly improve DH and enhance the antioxidant activity of WPC hydrolysates. Furthermore, F1 fraction (Mw> 10 kDa) showed the highest antioxidant and antibacterial activities mainly in the combined pretreatments. Finally, it was concluded that the combination of ultrasound and ohmic heating could generate WPC hydrolysates with enhanced ingredient functionality.

The Determination Method of Hydrolysis Degree of Natural Protein and Other Hydrolysates

For the determination of the hydrolysis degree of natural protein and other hydrolysates, the traditional determination method is not the best, and the determination effect is not good, so a new determination method of hydrolysis degree of natural protein and other hydrolysates is proposed. According to the activity of the protein, the release rate of the inhibitory peptide in hydrolysates was determined; the protein separation program was set up and the natural protein was purified; factors affecting protein activity were analyzed and the properties of protein molecules were extracted; the antioxidant activity of hydrolysates was calculated to obtain the optimal conditions of hydrolyzed protein and achieve the accurate prediction of hydrolysis. The experimental results show that compared with the traditional determination method, the proposed determination method has the best hydrolysis conditions, and the determined hydrolysis is consistent with the actual situation. It can be seen that this method is more suitable for the determination of hydrolysis degree of natural protein and other hydrolysates.

Ultrasonic pretreatment improved the antioxidant potential of enzymatic protein hydrolysates from highland barley brewer's spent grain (BSG).

Highland barley brewer's spent grain (BSG), being China's brewing industry's major by-product is the focus of current research. The aim of the present study was to scrutinize the effects of ultrasound and heat pretreatments on enzymatic hydrolysis of highland barley BSG protein hydrolysates (HBSGPH) and evaluate the effect of enzymatic hydrolysis time on the antioxidant activity of hydrolysates by Alcalase. Different ultrasonic waves (40 and 50kHz) and heat pretreatment temperatures (50 and 100 °C) were chosen and the pretreatment time was 15, 30, and 60min. The obtained results revealed that the ultrasound pretreatment of highland barley BSG protein at 40 and 50kHz has significantly (P <0.05)enhanced about 57 and 67% of oxygen radical absorption capacity of obtained hydrolysate over the untreated substrate. The 1,1-diphenyl-2-picrylhdrazl (DPPH) radical scavenging activity (DRSA) 28%, metal chelating activity (MCA) 54%, superoxide radical scavenging activity (SRSA) 18%, and hydroxyl radical scavenging activity (HRSA) 25% of HBSGPH at 50kHz were also improved (P <0.05)significantly. HBSGPH from heat treatment at 100 °C showed no SRSA and HRSA scavenging activities but improved significantly (P <0.05)about 27% ferric reducing antioxidant power (FRAP) assay values. In the present work, the resultant HBSGPH had stronger antioxidant properties with ultrasound pretreatment at 50kHz and the enzymatic hydrolysis after 4hr was facilitating the enzymatic release of antioxidant peptides from HBSGPH. PRACTICAL APPLICATION: Highland barley BSG is attracting toward natural food products due to its potent natural antioxidants to overcome the risk of diseases and are beneficial for human health.

Effects of High-Intensity Ultrasound Pretreatment on Structure, Properties, and Enzymolysis of Soy Protein Isolate.

The objective of this study was to investigate the effects of different high-intensity ultrasonication (HIU) pretreatment on the structure and properties of soybean protein isolate (SPI) as well as enzymatic hydrolysis of SPI by bromelain and antioxidant activity of hydrolysates. The HIU-treated SPI fractions showed a decrease in the proportion of α-helices and β-turns and an increase in the content of β-sheets and random coils based on Fourier-transform infrared spectroscopy. Near-infrared spectra and fluorescence spectra analyses provided support for the changes in secondary and tertiary structures of SPI after ultrasound treatment. The particle size of SPI decreased from 217.20 nm to 141.23 nm and the absolute zeta potential increased. Scanning electron microscopy showed that HIU treatment changed apparent morphology. Dynamic and static light scattering of ultrasonicated samples showed that SPI structure had changed from hard-sphere to hollow-sphere or polydisperse and monodisperse gaussian coils. HIU pretreatment significantly increased the hydroxyl-radical scavenging and the degree of hydrolysis of the SPI hydrolysates.

Effect of high‐pressure treatment prior to enzymatic hydrolysis on rheological, thermal, and antioxidant properties of lentil protein isolate

AbstractThe objective of the present work was to assess the effectiveness of high‐pressure (HP) treatment on the enzymatic hydrolysis of lentil protein (LP) in order to improve functionality and antioxidant activity of hydrolysates. LP dispersions were subjected to HP treatment in the selected pressure levels (300, 450, and 600 MPa for 15 min) prior to hydrolysis with alcalase (0.5% and 1%, w/w). The postprocess samples were analyzed to assess the impact of pressure treatment on denaturation, the degree of hydrolysis (DH), and antioxidant activity of hydrolysate. HP treatment improved the %DH of the LPI (p ≤ 0.05). The HP‐assisted alcalase hydrolysis imparted significant changes on the secondary structure of protein with a shift of amide I and amide II bands. The hydrolysis of LP was further confirmed by a significant drop on the enthalpy (ΔH) values in the DSC endothermic peaks and decreasing the steady shear viscosity. The pressurized protein hydrolysates attained an improvement in the foaming properties (≈1.5 times) and antioxidant activities (≈2 times) than the control hydrolysates. However, a detrimental effect was pronounced on the emulsifying activity and stability index, foam stability, and water holding capacity. These results could be useful for food industries to develop products using hydrolysates as protein supplements.

Production and characterisation of duck albumen hydrolysate using enzymatic process

SummaryInfluences of different ultrasound treatments combined with heat pretreatment on enzymatic hydrolysis, emulsifying properties and antioxidant activities of hydrolysates from duck egg albumen were studied. Heat pretreatment at 95 °C for 30 min inhibited both serine and cysteine protease inhibitors effectively. Ultrasonication of heated duck albumen at 60% amplitude for 10 min yielded the highest surface hydrophobicity. Coincidentally, aforementioned pretreatment rendered the hydrolysate with highest degree of hydrolysis (DH) than other pretreatments when Alcalase was used. The resulting hydrolysate showed the highest antioxidant activities including DPPH radical and ABTS radical cation scavenging activities and ferric reducing antioxidant power as well as emulsifying properties when hydrolysis time of 90 min was used. The hydrolysate possessed the peptides with molecular weight of 219–255 Da with the highest ABTS radical scavenging activity. Thus, heat pretreatment, followed by ultrasonication of duck albumen under appropriate condition could increase DH, antioxidant activities and emulsifying properties of duck albumen hydrolysate.

Antioxidant and cryoprotective effects of hydrolysate from gill protein of bighead carp (Hypophthalmichthys nobilis) in preventing denaturation of frozen surimi

This work aimed to evaluate the efficacy of protein hydrolysates from bighead carp gill in inhibiting protein oxidation and quality loss in surimi. Firstly, antioxidant activity of hydrolysates in vitro was assessed, then 1%, 2% hydrolysates with better antioxidant activity and 4% sucrose were added to surimi respectively and stored at −18 °C for 4 months. Peptide sequences of above hydrolysates were also identified. The results suggested that hydrolysates of neutral protease had excellent 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability (42.93%) and Fe2+-chelating activity (73.27%). Compared with surimi without treatments, surimi with hydrolysates had higher sulfhydryl and salt-soluble protein concentrations, greater Ca2+-ATPase activity, lower disulfide bonds, carbonyls and hydrophobicity, as well as better gel strength and texture (p < 0.05). This study demonstrated that gill hydrolysate had antioxidant and dose-dependent cryoprotective effects on surimi that were comparable to the effects of sucrose, representing it as an alternative to sugar cryoprotectants in surimi industry.

Antioxidant Assessment of Schizochytrium Meal Protein Enzymatic Hydrolysate and Its Potential Application

ABSTRACTSchizochytrium meal protein (SMP) extracted from Schizochytrium meal was hydrolyzed by flavourzyme. Response surface methodology (RSM) was used to optimize the extraction conditions for the protein extraction yield from Schizochytrium meal. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (DRSA) was used to evaluate the antioxidant activity of hydrolysates. The orthogonal test was used to investigate the effects of three independent variables, namely protease dosage, hydrolysis time, and pH. The optimum conditions obtained were as follows: protease dosage of 7%, hydrolysis time of 1.5 h, pH of 6, under which, DRSA at the concentration of 2 mg/mL was 89.38%. Aspartic and glutamic acid constituted approximately 26.32% of the total amino acids, and glutamic acid was the most abundant amino acid of Schizochytrium meal protein hydrolysate (SMPH) by amino acid composition analysis, which may have contributed to the scavenging activity of SMPH. Moreover, SMPH was made into chewable tablets with suitable formula and high humidity stability. These findings indicate that Schizochytrium meal can be reused as a raw material for preparation of antioxidant peptides.

Antioxidant Activities of Hydrolysates from Abalone Viscera Using Subcritical Water-Assisted Enzymatic Hydrolysis

Antioxidant hydrolysates were prepared from abalone viscera using subcritical water (AVS)-assisted by enzymatic hydrolysis with papain (AVSE-P), bromelain (AVSE-B), neutral protease (AVSE-N), and flavourzyme (AVSE-F). The protein and carbohydrate contents reached 38.33% and 24.36%, respectively. When AVS was digested by any of the proteases, the protein content increased, but carbohydrate content decreased. The main amino acids of AVSEs included alanine, glycine, and aspartic acid. The IC50 values of ferric reducing antioxidant power, and 2,2-diphenyl-1-picrylhydrazyl (DPPH)•, 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)•+, N,N-Dimethyl-p-phenylenediamine dihydrochloride (DMPD)•+, and hydroxyl radical (•OH) scavenging abilities of AVS were 2.93, 1.48, 1.61, 3.72, and 5.51 mg/mL, respectively, which decreased after enzymatic hydrolysis by any of the proteases. The DMPD•+ and •OH scavenging abilities of AVSE-P and AVSE-B were higher than those of others, whereas the opposite was observed in lipid peroxidation inhibition efficiency, DPPH•, and ABTS•+ scavenging abilities. Hence, antioxidant activities of AVS could be enhanced by enzymatic hydrolysis, but the influence depends on the type of protease. At the same time, results also suggest that the proposed approach can be used for treating abalone viscera, and the obtained antioxidant hydrolysates could be used in nutraceutical and pharmaceutical industries.

Effects of combined high pressure and enzymatic treatments on physicochemical and antioxidant properties of peanut proteins.

Isolated peanut protein (PPI) dispersions were pretreated by high pressure at 100, 300, and 500 MPa prior to enzymatic hydrolysis with alkaline protease (Alcalase). The degree of hydrolysis (DH) was determined by the pH‐stat method, the hydrolysates profiles were analyzed by high‐performance liquid chromatography (HPLC), the molecular weight distribution (MWD) was analyzed by gel filtration chromatogram (GFC), and content of SH/S‐S and antioxidant activity of hydrolysates were evaluated. Results showed that HP pretreatment improved effectively the enzymatic hydrolysis of PPI, with an effective sequence of 300 > 100 > 500 MPa. However, no significant differences were observed in the peak pattern of HPLC profiles, but the peak times were earlier in HPLC profiles of the HP‐treated protein. GFC analysis showed that more peptide fractions with low molecular weight appeared in the hydrolysates of the HP‐treated PPI with increasing pressure. Moreover, the level of free SH of hydrolysates of the HP‐treated PPI was relatively higher than non‐HP‐treated PPI. The hydrolysates of the HP‐treated PPI exerted higher antioxidant activity (reducing power and DPPH radical scavenging) than the hydrolysates of non‐HP‐treated PPI. The results indicated that high pressure treatment affected the enzymatic hydrolysis of peanut protein and some protein structure properties and improved antioxidant activity of PPI hydrolysates.

Optimizion of enzymatic hydrolysis of zein to prepare protein hydrolysate with increased antioxidants

Background: Protein hydrolysate was prepared with zein recycled from corn gluten meal. It have been reported that zein have the antioxidant activity. Various recycling methods were selected to obtain zein with desirable characteristics, but ignored the antioxidant activity of hydrolysate. No comparisons of different recycling methods of zein or studies on the use of RSM to optimize enzymatic hydrolysis conditions to increase antioxidant activity could be found. Materials and Methods: The corn gluten meal used in this study was a gift from the Xiwang group in China. Zein was dis-colored from corn gluten meal by alcohol (1:6) under ultrasound (Elmasonic S50R, German) twice for 15 min each time. Zein was extracted through preliminary optimized conditions of 55% ethanol at 38°C for 15 min. The extracted zein was placed in a beaker before use. Results: The optimum conditions to obtain a high DPPH radical scavenging rate was close to the predicted value (7.523%, 0.0416 mg/mL ascorbate equiv), and they were as follows: an enzyme to substrate level of 1% (w/w), temperature of 40°C, time of one hour, and pH of 8. HPLC detected more than 26 constituents in the zein hydrolysate, and the content of glutamic acid rose at a relatively high degree from 16.8 to 19.1. Conclusion: The best recycling method for colourless zein with high antioxidant activity was dilutionfreeze- drying. The zein including hydrolysate has potential for applications in functional foods, which would significantly improve the added value.