Effect of limited enzymatic hydrolysis on physico‐chemical properties of soybean protein isolate‐maltodextrin conjugates

The effect of limited hydrolysis was investigated on the physico‐chemical properties of soy protein isolate–maltodextrin (SPI‐Md) conjugate. The hydrolysates at a degree of hydrolysis (DH) of 1.8% showed much higher surface hydrophobicity (H₀; 71.39 ± 3.60) than that of the SPI control (42.09 ± 2.17) and SPI‐Md conjugates (53.46 ± 2.74). Intrinsic fluorescence analysis demonstrated the unfolding of protein molecule and exposure of hydrophobic groups of SPI‐Md conjugate hydrolysates. As evidenced by far‐UV circular dichroism (CD) spectroscopy, the limited hydrolysis increased the unordered secondary structures of SPI‐Md conjugates. The denaturation temperature (T_d) of SPI‐Md conjugate was significantly increased by subsequent limited hydrolysis from 102.53 ± 0.60 °C to 108.11 ± 0.61 °C at DH 1.8%. In particular, the emulsifying activity index (EAI) was improved notably after limited hydrolysis of DH 1.8% (147.76 ± 4.39 m² g^?1) compared with that of native SPI (88.90 ± 1.44 m² g^?1) and SPI‐Md conjugate (108.97 ± 1.45 m² g^?1).     

Biochemical properties and antioxidant activity of myofibrillar protein hydrolysates obtained from patin (Pangasius sutchi)

Antioxidant activities of myofibrillar protein hydrolysates (MPH) prepared from patin (Pangasius sutchi) using papain and Alcalase^® 2.4 L with different degrees of hydrolysis (DH) were investigated. With a DH of 65.83%, the hydrolysate prepared with papain exhibited the maximum of 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical‐scavenging activity (71.14%) with a reducing power of 0.310. At a concentration of 1 mg mL^?1, the papain‐MPH exhibited a Trolox equivalent antioxidant capacity (TEAC) of 70.50 ± 1.22 μmol g^?1 protein. With a DH of 83.6%, the Alcalase‐MPH had the highest metal‐chelating activity. Low molecular weight peptides showed higher antioxidant activities than high molecular weight peptides. Both papain‐MPH and Alcalase‐MPH contained high amounts of the essential amino acids (48.71% and 48.10%, respectively) with glutamic acid, aspartic acid and lysine as the dominant amino acids. These results suggest that the protein hydrolysates derived from patin may be used as an antioxidative ingredient in both functional food and nutraceutical applications.     

Functional Properties and Bioactivities of Pine Nut (Pinus gerardiana) Protein Isolates and Its Enzymatic Hydrolysates

The functional properties and bioactivities of the pine nut protein isolates (PPI) and its enzymatic hydrolysates (PPH) prepared with Alcalase at 5 %, 10 %, 15 % and 25 % degree of hydrolysis (DH) were studied. The solubility of PPH significantly increased (p?<?0.05) with the increase of the DH, while the foaming capacity of PPH was only improved at a low DH. However, enzymatic hydrolysis reduced the emulsifying capacity of PPH. The DPPH radical scavenging and inhibition of linoleic acid oxidation activities of PPH were significantly improved by a low DH (5 %) compared with those of PPH with a higher DH and the original PPI (p?<?0.05). The reducing power of PPH at all DH decreased in comparison to that of the original PPI. Potent angiotensin-converting enzyme (ACE) inhibitory peptides could be generated by hydrolysis with Alcalase, and the ACE inhibitory activity of PPH increased (p?<?0.05) with the DH. These results revealed that a low degree of enzymatic hydrolysis was appropriate to obtain PPH with improved functional properties and good antioxidant activities, while a high degree of hydrolysis was essential to obtain highly potent ACE inhibitory peptides from PPI. These results suggest that the control of the DH may be an effective strategy to modify specific functional and bioactive properties of PPH, and PPH has potential as a functional food ingredient for related functional and health benefits.     

Influence of degree of hydrolysis on functional properties and angiotensin I‐converting enzyme‐inhibitory activity of protein hydrolysates from cuttlefish (Sepia officinalis) by‐products

BACKGROUND: In Tunisia the cuttlefish‐processing industry generates large amounts of solid wastes. These wastes, which may represent 35% of the original material and constitute an important source of proteins, are discarded without any attempt at recovery. This paper describes some functional properties and the angiotensin I‐converting enzyme (ACE)‐inhibitory activity of protein hydrolysates prepared by hydrolysis of cuttlefish (Sepia officinalis) by‐products with crude enzyme extract from Bacillus licheniformis NH1. RESULTS: Cuttlefish by‐product protein hydrolysates (CPHs) with different degrees of hydrolysis (DH 5, 10 and 13.5%) were prepared. All CPHs contained 750–790 g kg^?1 proteins. Solubility, emulsifying capacity and water‐holding capacity increased while fat absorption and foaming capacity decreased with increasing DH. All hydrolysates showed greater fat absorption than the water‐soluble fraction from undigested cuttlefish by‐product proteins and casein. CPHs were also analysed for their ACE‐inhibitory activity. CPH3 (DH 13.5%) displayed the highest ACE inhibition (79%), with an IC₅₀ value of 1 mg mL^?1. CONCLUSION: Hydrolysis of cuttlefish by‐product proteins with alkaline proteases from B. licheniformis resulted in a product with excellent solubility over a wide pH range and high ACE‐inhibitory activity. This study suggests that CPHs could be utilised to develop functional foods for prevention of hypertension. Copyright © 2010 Society of Chemical Industry     

Functional and bioactive properties of Velvet bean (Mucuna pruriens) protein hydrolysates produced by enzymatic treatments

Velvet bean (Mucuna pruriens) protein hydrolysates were produced with gastrointestinal enzymes. Functional properties such as nitrogen solubility, emulsifying capacity and emulsion stability, foam capacity and stability of the hydrolysates were determined. Angiotensin I-converting enzyme inhibitory, antioxidant and antithrombotic capacities were evaluated to determine the biological activity of hydrolysates. For pepsin, degree of hydrolysis (DH) increased sharply between 5 min (22.33 %) and 60 min (28.07 %), respectively, with a maximum DH of 33.50 % (90 min). For pancreatin, DH increased sharply between 5 min (25.08 %) and 90 min (34.92 %), respectively, with a maximum DH of 37.23 % (120 min). For sequential system pepsin–pancreatin, DH increased sharply between 5 min (25.21 %) and 60 min (32.82 %), respectively, with a maximum DH of 34.14 % (120 min). Hydrolysates with the lowest DH and the highest DH were selected to assess the functional and biological potential. Mucuna pruriens limited hydrolysates can be considered a useful food additives to provide functional properties, while M. pruriens extensive hydrolysates can be used as nutraceutical ingredients.     

Angiotensin‐I converting enzyme inhibitory and antioxidant activities of peptide fractions extracted by ultrafiltration of cowpea Vigna unguiculata hydrolysates

BACKGROUND: Enzymatic proteolysis of food proteins is used to produce peptide fractions with the potential to act as physiological modulators. Fractionation of these proteins by ultrafiltration results in fractions rich in small peptides with the potential to act as functional food ingredients. The present study investigated the angiotensin‐I converting enzyme (ACE‐I) inhibitory and antioxidant activities for hydrolysates produced by hydrolyzing Vigna unguiculata protein extract as well as ultrafiltered peptide fractions from these hydrolysates. RESULTS: Alcalase^®, Flavourzyme^® and pepsin–pancreatin were used to produce extensively hydrolyzed V. unguiculata protein extract. Degree of hydrolysis (DH) differed between the enzymatic systems and ranged from 35.7% to 58.8%. Fractionation increased in vitro biological activities in the peptide fractions, with IC₅₀ (hydrolysate concentration in µg protein mL^?1 required to produce 50% ACE inhibition) value ranges of 24.3–123 (Alcalase hydrolysate, AH), 0.04–170.6 (Flavourzyme hydrolysate; FH) and 44.7–112 (pepsin–pancreatin hydrolysate, PPH) µg mL^?1, and TEAC (Trolox equivalent antioxidant coefficient) value ranges of 303.2–1457 (AH), 357.4–10 211 (FH) and 267.1–2830.4 (PPH) mmol L^?1 mg^?1 protein. CONCLUSION: The results indicate the possibility of obtaining bioactive peptides from V. unguiculata proteins by means of a controlled protein hydrolysis using Alcalase^®, Flavourzyme^® and pepsin–pancreatin. The V. unguiculata protein hydrolysates and their corresponding ultrafiltered peptide fractions might be utilized for physiologically functional foods with antihypertensive and antioxidant activities. Copyright © 2010 Society of Chemical Industry     

Effect of combined treatment of hydrolysis and polymerization with transglutaminase on β-lactoglobulin antigenicity

The effect of combined treatments of hydrolysis with different proteases, and subsequent polymerization with transglutaminase on the antigenic activity of β-Lg was studied. For the hydrolysis of β-Lg using Alcalase, Neutrase or bromelain, the reaction conditions were 3?% β-Lg and enzyme:substrate 25?U?g^?1 of protein, as was defined using factorial study. Under these conditions, the degree of hydrolysis (DH) of the hydrolysates was 12.6?% when obtained with Alcalase and approximately 4?% with Neutrase or bromelain. Post-hydrolysis polymerization did not result in an increase in molecular mass of the protein, but these samples presented a lower DH, determined by trinitrobenzenosulfonic acid (TNBS) method, suggesting that polymerization had occurred. Hydrolysis with the three enzymes reduced the β-Lg antigenicity, as evaluated by ELISA and immunoblotting analyses. The IgE-binding responses were practically null (<9?μg?mL^?1), 22.82 and 55.73?μg?mL^?1 towards the hydrolysates obtained with Alcalase, bromelain, and Neutrase, respectively. The post-hydrolysis polymerization increased or had no significant effect (P?≥?0.05) on the antigenic response of the hydrolysates.     

Optimisation of hydrolysis of purple sea urchin (Strongylocentrotus nudus) gonad by response surface methodology and evaluation of in vitro antioxidant activity of the hydrolysate

BACKGROUND: Hydrolysates prepared from sea urchin (Strongylocentrotus nudus) gonad by enzymatic treatment showed strong 1,1‐diphenyl‐2‐picrylhydrazyl radical scavenging activity and reducing power. RESULTS: Hydrolysis of S. nudus gonad by the commercial protease papain was optimised for maximum degree of hydrolysis (DH) and trichloroacetic acid‐soluble peptide index (TCA‐SPI) using response surface methodology. Results showed that the optimal conditions were the following: temperature of 48.83 °C, pH of 6.92, enzyme‐to‐substrate ratio of 3143 U g^?1, and substrate concentration of 83.5 g L^?1. Under these conditions, a DH of 27.96 ± 0.54% and a TCA‐SPI of 57.32 ± 0.63% were obtained. The hydrolysate prepared in the optimal conditions was fractionated by an ultra‐filtration system and the resultant fraction below 10 kDa was found to effectively scavenge hydroxyl radical (EC₅₀ = 13.29 ± 0.33 mg mL^?1) and hydrogen peroxide (EC₅₀ = 16.40 ± 0.37 mg mL^?1), inhibit lipid peroxidation (EC₅₀ = 11.05 ± 0.62 mg mL^?1), chelate Fe²⁺ (EC₅₀ = 7.26 ± 0.44 mg mL^?1), and protect mice macrophages against death induced by tert‐butyl hydroperoxide. CONCLUSION: Hydrolysates prepared from S. nudus gonad have the potential to be applied as natural antioxidant agents. Copyright © 2012 Society of Chemical Industry     

Antioxidant properties of porcine liver proteins hydrolyzed using <Emphasis Type="Italic">Monascus purpureus</Emphasis>

In this study, the antioxidant activities of porcine liver proteins, hydrolyzed using Alcalase^®, papain, pepsin, or a microbial suspension of Monascus purpureus (APLH, PaPLH, PePLH, and MPLH, respectively), were investigated. The results indicated that the yield and degree of hydrolysis (DH) of hydrolysates increased with hydrolysis time. The highest yield and peptide content were obtained from APLH, whereas the DH of PaPLH was higher than that of the others. MPLH exhibited the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and reducing power, whereas APLH and PaPLH exhibited the higher ferrous ion-chelating ability than that of the MPLH. The molecular weights of all the hydrolysates were <10 kDa. The PaPLH exhibited the highest contents of total amino acids and hydrophobic amino acids. Fifteen antioxidant fractions obtained from MPLH contained one or more of the following amino acids in their sequences: Tyr, Trp, Ala, Pro, Met, Lys, Asp, Cys, Val, Leu, and His.     

Antioxidant activities and functional properties of soy protein isolate hydrolysates obtained using microbial proteases

Soy protein isolate (SPI) hydrolysates were prepared using microbial proteases to produce peptides with antioxidant activity. The process parameters (substrate and enzyme concentrations), hydrolysis time, functional properties and the effects of ultrafiltration were further investigated. The results showed that the soy protein isolate exhibited a 7.0‐fold increase in antioxidant activity after hydrolysis. The hydrolysis parameters, defined by the experimental design, were a substrate concentration of 90 mg mL^?1 and the addition of 70.0 U of protease per mL of reaction. The maximum antioxidant activities were observed between 120 and 180 min of hydrolysis, where the degree of hydrolysis was approximately 20.0%. The hydrolysis increased solubility of the soy protein isolate; however, the hydrolysates exhibited a tendency to decrease in the interfacial activities and the heat stability. The SPI hydrolysates fractions obtained by ultrafiltration showed that the enzymatic hydrolysis resulted in samples with homogenous size and strong antioxidant activity.     

Antioxidant activities and functional properties of grass carp (Ctenopharyngodon idellus) protein hydrolysates

BACKGROUND: Grass carp, with an annual production exceeding 4 × 10⁶ t in China in 2009, has not been developed into a high‐value product. In this study the antioxidant activities and functional properties of grass carp protein hydrolysates prepared with Alcalase 2.4L (HA) and papain (HP) were investigated. The hydrolysate with strongest radical‐scavenging activity and reducing power was assessed further for changes in its antioxidant activity during simulated gastrointestinal digestion. RESULTS: As the degree of hydrolysis (DH) increased, the metal‐chelating activity of both HA and HP increased while their reducing power and 1,1‐diphenyl‐2‐picrylhydrazyl radical (DPPH^?)‐scavenging activity decreased (P < 0.05). At the same DH, HP possessed higher DPPH^?‐scavenging activity and reducing power than HA (P < 0.05). The metal‐chelating activity of HP with 10% DH was significantly increased after in vitro gastrointestinal metabolism (P < 0.05). Regarding their functional properties, all hydrolysates were more than 81% soluble over a wide range of pH (3–8). At the same DH, HP showed higher emulsion activity index but lower solubility and foaming capacity than HA. CONCLUSION: Grass carp protein hydrolysates showed high solubility over a wide pH range and could be used as natural antioxidants in food systems. Copyright © 2011 Society of Chemical Industry     

琥珀酸脱酰胺对小麦面筋蛋白酶解产物抗氧化性的影响

研究琥珀酸不同脱酰胺程度对小麦面筋蛋白胰酶的酶解产物抗氧化性的影响。在相同水解度下,以DPPH.清除率、.OH清除率、ORAC值为抗氧化指标,结果表明低脱酰胺程度(22.4%)的小麦面筋蛋白酶解产物的抗氧化性有较大幅度的提高,高脱酰胺程度(60.4%)的小麦面筋蛋白酶解产物的抗氧化性降低。水解度15%的酶解产物的肽分子量分布表明,低脱酰胺的小麦面筋蛋白酶解产物中分子量小于3000u的肽段增加,高脱酰胺的小麦面筋蛋白酶解产物中分子量小于3000u的肽段减少;在相同水解度下的氨基酸分析结果表明,脱酰胺后的小麦面筋蛋白酶解生成的肽的疏水性和抗氧化性的氨基酸含量提高。因此,低脱酰胺的小麦面筋蛋白酶解产物抗氧化性提高的主要原因是产物中含疏水性和抗氧化性氨基酸的小分子肽含量提高。      

Glutaminase‐induced deamidation and hydrolysis of casein and metal‐chelating or ACE‐inhibitory activity of the hydrolysates in vitro

Glutaminase (EC 3.5.1.2) was applied in this work to induce deamidation and hydrolysis of casein. Some reaction conditions based on casein deamidation were studied. Three casein hydrolysates with degree of deamidation of 2.8%, 5.8% and 8.5%, or degree of hydrolysis of 2.5%, 3.4% and 4.9%, respectively, were prepared at casein concentration 5% (w/v), glutaminase addition level 400 U kg^?1 casein, reaction temperature 37 °C and reaction times 6, 12 and 24 h, respectively. Evaluation results showed that when iron (II) was added at 60 μm , iron (II)‐chelating powers of three hydrolysates were 41.1, 45.4 and 55.3%, while that of original casein and EDTA were 36.1 and 13.6%. Calcium (II)‐chelating power of three hydrolysates was 1.23, 1.41 and 1.49 mmol g^?1 casein, whereas that of original casein was 1.05 mmol g^?1 casein. Three hydrolysates also had ACE‐inhibitory activity in vitro, with IC₅₀ values from 0.75 to 2.34 mg mL^?1.     

Improvement of emulsifying properties of Maillard reaction products from β-conglycinin and dextran using controlled enzymatic hydrolysis

A novel emulsifier was prepared by conjugating soy β-conglycinin and dextran (MW 67 kDa) under dry-heated Maillard reaction followed by trypsin hydrolysis with the degree of hydrolysis (DH) at 2.2% and 6.5%. The emulsifying properties of β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates (DH 2.2% and DH 6.5%) were investigated using zeta-potential, droplet size and creaming index of the emulsions. The results showed that hydrolysates of β-conglycinin–dextran conjugates (DH 2.2%) were capable of forming a fine emulsion (d₄₃ = 0.62 ± 0.04 μm, pH 7.0) which remained stable during 4 weeks of storage. A variety of physicochemical and interfacial properties of β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates were investigated. Hydrolysates of β-conglycinin–dextran conjugates (DH 2.2%) had a much higher fraction of protein adsorption (F_ads) and a significantly lower saturation surface load (Γ_sat) compared with β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates (DH 6.5%). This might be due to its higher molecular flexibility, which benefited the adsorption and unfolding of peptide molecules at the droplet interface. These might explain its markedly improved emulsifying capability. The conjugation of β-conglycinin and dextran effectively enhanced the hydrophilicity of the oil droplets surfaces and improved the steric repulsion between the oil droplets. Therefore the emulsions were still stable after 4 weeks of storage against pH, ionic strength and thermal treatment. This study demonstrated that controlled enzymatic hydrolysis of protein–polysaccharide conjugates could be an effective method for preparing favourable emulsifiers.     

Sweet potato protein hydrolysates: antioxidant activity and protective effects on oxidative DNA damage

In this study, sweet potato protein (SPP) hydrolysates were prepared by six enzymes (alcalase, proleather FG‐F, AS1.398, neutrase, papain and pepsin). The antioxidant activities and protective effect against oxidative DNA damage of SPP hydrolysates were investigated. Alcalase hydrolysates exhibited the highest hydroxyl radical‐scavenging activity (IC₅₀ 1.74 mg mL^?1) and Fe²⁺‐chelating ability (IC₅₀ 1.54 mg mL^?1) (P < 0.05). Compared with other five hydrolysates, the hydrolysates obtained by alcalase had the most abundant <3‐kDa fractions. In addition, below 3‐kDa fractions of alcalase hydrolysates showed the highest antioxidant activities and protective effects against DNA damage through both scavenging hydroxyl radicals and chelating Fe²⁺, which was probably because of the increase in several antioxidant amino acids, such as His, Met, Cys, Tyr and Phe, as well as the hydrophobic amino acids. The results suggested that enzymatic hydrolysis could be used as an effective technique to produce high value‐added peptides products from SPP.     

Optimisation, by response surface methodology, of degree of hydrolysis and antioxidant and ACE-inhibitory activities of whey protein hydrolysates obtained with cardoon extract

The hydrolysis of bovine whey protein concentrate (WPC), α-lactalbumin (α-La) and caseinomacropeptide (CMP), by aqueous extracts of Cynara cardunculus, was optimized using response surface methodology. Degree of hydrolysis (DH), angiotensin-converting enzyme (ACE)-inhibitory activity and antioxidant activity were used as objective functions, and hydrolysis time and enzyme/substrate ratio as manipulated parameters. The model was statistically appropriate to describe ACE-inhibitory activity of hydrolysates from WPC and α-La, but not from CMP. Maximum DH was 18% and 9%, for WPC and α-La, respectively. 50% ACE-inhibition was produced by 105.4 (total fraction) and 25.6 μg mL⁻¹ (<3 kDa fraction) for WPC, and 47.6 (total fraction) and 22.5 μg mL⁻¹ (<3 kDa fraction) for α-La. Major peptides of fractions exhibiting ACE-inhibition were sequenced. The antioxidant activities of WPC and α-La were 0.96 ± 0.08 and 1.12 ± 0.13 μmol trolox equivalent per mg hydrolysed protein, respectively.     

Antioxidant function of tea dregs protein hydrolysates in liposome–meat system and its possible action mechanism

Tea dregs possess abundant proteins, and the objective of this study was to investigate the antioxidant activity of tea dregs protein hydrolysate with limited hydrolysis by protamex and its possible action mechanism. Tea dregs protein was hydrolysed by alcalase, protamex or neutrase. The hydrolysis condition was optimised, and the hydrolysate was characterised for 1,1‐diphenyl‐2‐picryl hydrazyl (DPPH) radical‐scavenging activity, hydroxyl radical‐scavenging activity and antioxidant activity in linoleic acid (LA) system and in chicken products. Tea dregs protein hydrolysate (TDPH) was formulated (0.1%, 0.5%, 1.0%, w/w) into chicken products to determine in situ antioxidant efficacy. Thiobarbituric acid‐reactive substances (TBARS) and peroxide value (POV) formed in chicken products during storage (4 °C, 0–7 days) were analysed. Results showed that the optimum hydrolysis condition was at 50 °C, pH 7.0 for 20 min, and the concentration of tea dregs protein was 1.5%; ratio of protamex to substrate was 6000 U g^?1. The radical‐scavenging ratio of TDPH to 1,1‐diphenyl‐2‐picryl hydrazyl (DPPH) was 90.30% at the concentration of 0.1 mg mL^?1 and that to hydroxyl radical was 65.18% at the concentration of 1.0 mg mL^?1. Moreover, it also showed strong antioxidant activity both in linoleic acid (LA) system and in chicken products. The molecular weight distribution of tea dregs hydrolysates was determined by nanofiltration tubular membrane, and the protein hydrolysates with molecular weight above 8000 Da had more effective antioxidant activity. The radical‐scavenging activities to DPPH and hydroxyl radical were 85.72% at 0.1 mg mL^?1 and 71.52% at 1.0 mg mL^?1, respectively. These findings suggest that the enzymatic hydrolysate of tea dregs protein probably possesses the specific peptides/amino acids which could stabilise or terminate the radicals through donating hydrogen. In addition, the hydrolysate could form a physical barrier around the fat droplets.     

金带细鲹鱼肉蛋白酶解物水解度与其抗氧化性和功能特性间的相互关系

采用胰蛋白酶水解金带细鲹鱼肉蛋白制备不同水解度(10.8%、14.9%、19.0%和21.7%)的酶解产物,研究水解度与酶解产物抗氧化性和功能特性的关系。抗氧化性分析表明,低水解度处理显著增大了酶解物清除羟基自由基的能力、清除DPPH自由基的能力和螯合亚铁离子的能力(p<0.05),而高水解度处理则增强了酶解产物的金属还原力(p<0.05)。功能特性结果表明:随着水解度的增大,酶解产物的溶解度逐渐增大,而乳化活性和乳化稳定性逐渐降低,起泡性和泡沫稳定性也降低。同时,随着p H的增加,酶解物的溶解性和乳化稳定性呈先下降后上升的趋势,而起泡性和泡沫稳定性则随着p H的增加而降低。上述分析表明,适当的酶解处理对改善金带细鲹鱼肉蛋白的功能特性及抗氧化活性具有一定的作用。      

Compositions and antioxidant properties of protein hydrolysates from the skins of four carp species

Compositions and antioxidant properties of protein hydrolysates prepared from four carp skins: black carp, grass carp, silver carp and bighead carp, using pepsin, with a degree of hydrolysis (DH) of 6–15%, were investigated. The yield of freeze‐dried hydrolysates was in the range of 54–62 g/100 g (dry skin). The content of protein and ash in four freeze‐dried hydrolysates was 72–81% and 8–17%, respectively. All hydrolysates contained high amount of hydrophobic amino acid residues (389–480 residues/1000 residues). Meanwhile, their antioxidant properties were evaluated by in vitro assays. The results revealed that all hydrolysates possessed potent antioxidant activities and showed dose dependency as the activity increased with sample concentration, capable of scavenging 72–88% of DPPH and 61–69% of hydroxyl radicals, respectively, at the highest tested concentration. The hydrolysates exhibited high reducing power and β‐carotene–linoleic acid oxidation inhibition. Among the four hydrolysates, the hydrolysate derived from bighead carp skin was superior to others in terms of yield, DH and antioxidant activities.     

Physicochemical and antioxidant properties of buckwheat (Fagopyrum esculentum Moench) protein hydrolysates

The enzymatic hydrolysis of common buckwheat (Fagopyrum esculentum Moench) protein isolate (BPI) by Alcalase and some physiochemical and antioxidant properties of the resulting hydrolysates were characterised. The hydrolysis resulted in remarkable decrease in the globulins or protein aggregates and concomitant increase in peptide fragments. The surface hydrophobicity of the hydrolysates decreased with increasing degree of hydrolysis (DH) and reached a minimum at DH 15%, but increased at further hydrolysis, whereas their amino acid compositions were unchanged. The polyphenol content of the hydrolysates gradually decreased with DH increasing from 0% to 15%, while it on the contrary increased upon further hydrolysis. The hydrolysates exhibited excellent antioxidant activities, including DPPH radical scavenging ability, reducing power and ability to inhibit linoleic acid peroxidation. The antioxidant activities of these hydrolysates were closely related to their polyphenol contents. The results indicated that polyphenol-rich buckwheat proteins are unique protein materials for the production of the hydrolysates with good nutritional and antioxidant properties.