Improvement of thermal,microwave and ultrasonication pretreatment on the production of antioxidant peptides from sweet potato protein via in vitro gastrointestinal digestion

Effects of thermal (boiling, steaming and autoclaving), microwave and ultrasonication pretreatments on the production of sweet potato protein hydrolysates (SPPH) through in vitro gastrointestinal digestion (GID) were investigated. All pretreatments significantly increased the degree of hydrolysis (DH), antioxidant activities and molecular weight (MW) <3 kDa peptide fractions contents of SPPH in the order of autoclaving > microwave, steaming > boiling > ultrasonication (P < 0.05). Correlation analysis between peptides content and antioxidant activity suggested that antioxidant activity of SPPH mainly attributed to MW <3 kDa peptides. Diverse peptides ranged from 487.24 to 1477.74 Da with 7–13 amino acids were identified in the MW <3 kDa peptides fraction with autoclaving pretreatment and matched sporamins A, A precursor and B sequences from LC–QTOF–MS/MS analysis. Conformational structures of nine peptides were predicted with well-known antioxidant amino acids. There is a high potential for SPPH used as a functional supplement in food system.     

Grass carp peptides hydrolysed by the combination of Alcalase and Neutrase: Angiotensin‐I converting enzyme (ACE) inhibitory activity,antioxidant activities and physicochemical profiles

In this study, grass carp peptides were prepared by enzymatic hydrolysis of grass carp protein using the combination of Alcalase and Neutrase, and angiotensin‐I converting enzyme (ACE) inhibitory activity in vitro, antihypertensive activity in vivo, antioxidant activities, and physicochemical properties of peptides achieved from grass carp protein were characterised after ultrafiltration and desalted processes using mixed ion exchange resins. The purified peptides exhibited strong ACE inhibitory activity (IC₅₀ = 105 μg mL^?1), antihypertensive activity with the maximal drop for systolic blood pressure (SBP) of 43 mmHg at a dosage of 100 mg per kg body weight in spontaneously hypertensive rat (SHR), and antioxidant activities indicated by thiobarbituric acid‐reactive substance values in a liposome‐oxidising system, radical‐scavenging activity and chelation of metal ions (Fe²⁺). The molecular weight of peptides was <1000 Da. Compared to grass carp protein, the peptides separated from enzymatic hydrolysates possessed similar amino acid compositions, but contained higher concentrations of essential amino acids. Moreover, the peptides exhibited excellent solubility at a wide range of pH values from 2 to 10, and lower apparent viscosity than the protein. The peptides separated from enzymatic hydrolysates might be used as a promising ingredient in antihypertensive functional foods and nutraceuticals.     

Purification and characterisation of antioxidant and nitric oxide inhibitory peptides from Tilapia (Oreochromis niloticus) protein hydrolysate

Nitric oxide (NO)‐inhibitory and antioxidative activities of tilapia hydrolysates were prepared using ultrasound pretreatment at 70 W for 30 and 45 min, respectively, followed by Flavourzyme hydrolysis for 1 h. Both hydrolysates were fractionated using size exclusion chromatography on Sephadex G‐25 column and purified by RP‐HPLC. The amino acid sequence of the most potent and purified fractions was determined using LC/MS/MS. The antioxidant peptide (KAFAVIDQDKSGFIEEDELKLFLQNFSAGARAGDSDGDGKIGVDEFAALVK, MW: 6334.49 KDa) and NO‐inhibitory peptide (AFAVIDQDKSGFIEEDELKLFLQNFSAGARAGDSDGDGKIGVDEFAALVK, MW: 6309.49 Da) produced no cytotoxicity in RAW264.7 macrophage cell lines at the concentration of 100 mg mL^?1. The purified peptides at the concentration 100 μg mL^?1 possessed antioxidative and NO‐inhibitory activities 83.0 ± 1.1% and 40.9 ± 0.2%, respectively, which were about 100 times those of their counterpart crude hydrolysates.     

Isolation,purification and characterisation of angiotensin I‐converting enzyme–inhibitory peptides derived from catfish (Clarias batrachus) muscle protein thermolysin hydrolysates

The angiotensin I‐converting enzyme (ACE)‐inhibitory activities of catfish (Clarias batrachus) muscle protein hydrolysates were investigated. Thermolytic digests of C. batrachus sarcoplasmic and myofibrillar proteins exhibited inhibitory activity towards ACE and were purified with the aim of ultrafiltration, gel filtration and reversed‐phase high‐performance liquid chromatography (RP‐HPLC). The amino acid sequences of hydrolysates with the highest ACE‐inhibitory activities were determined using electrospray quadrupole time‐of‐flight tandem mass spectrometry (ESI‐TOFQ MS/MS). The sequences of GPPP (IC₅₀ = 0.86 μm ) and IEKPP (IC₅₀ = 1.2 μm ) corresponding to the fragments 986–989 and 441–445 of myosin‐I heavy chain were identified for the sarcoplasmic and myofibrillar protein hydrolysates, respectively. Peptide GPPP exhibited a mixed‐type inhibition whereas peptide IEKPP could only bind to the active sites of ACE. The results demonstrate that hydrolysates of C. batrachus muscle proteins obtained by thermolysin may contain bioactive peptides.     

Changes in bioactive compounds and their relationship to antioxidant activity in white sufu during manufacturing

In this article, samples of white sufu were collected at different manufacture stages and their content of water‐soluble protein (WSP) and amino nitrogen (AN); the distribution of peptides in WSP and isoflavones, as well as the antioxidant activities, was analysed. Results indicated that the peptides with molecular weight of 500–1000 Da increased 13.09 times from 0.11 to 1.44 g 100 g^?1 dry matter (DM) during the whole manufacturing, while isoflavone glucosides were almost entirely converted to aglycones after ripening for 15 days. Ferric reducing power (FRAP) and 2,2′‐azinobis‐3‐ethylbenzothiazoline‐6‐sulphonic acid radical scavenging activity (ABTS RSA) were significantly increased by 2.80‐ and 1.60‐fold, respectively. Correlation analysis suggested that ABTS RSA was significantly related to WSP (especially for the 500–1000 Da peptides; P < 0.01) and the content of aglycones (P < 0.05), while FRAP was only correlated to WSP (P < 0.05). It is concluded the peptides were the most important components contributing to the antioxidant activities of sufu.     

Evaluation of bioactive properties of peptide isolated from Exocoetus volitans backbone

The aim of this study was to evaluate antioxidant, antiproliferative and antimicrobial properties of flying fish (Exocoetus volitans) backbone hydrolysed by three different enzymes namely papain, pepsin and trypsin. The in vitro antioxidant potencies of hydrolysates and purified peptides against 1, 1‐diphenyl‐2‐picrylhydrazyl, superoxide and hydroxyl radicals were evaluated by electron spin resonance spectroscopy. The peptic protein hydrolysate showed maximum free radical scavenging potential and lipid peroxidation inhibition and was further purified by DEAE XK 26/20 anion exchange chromatography followed by G‐25 gel permeation chromatography. The amino acid composition of potent purified fraction was determined by HPLC, contains essential and nonessential amino acids with glutamic acid (24.10%), lysine (23.62%), glycine (12.05%) and threonine (10.41%) as the dominant amino acids. The potent purified fraction was tested for cell cytotoxicity on Vero and Hep G₂ cell lines. It was found that fraction IIIb did not show any cytotoxic effect for Vero cell lines and exerted a significant antiproliferative effect on Hep G₂ cell lines.     

Influence of the degree of hydrolysis (DH) on antioxidant properties and radical-scavenging activities of peanut peptides prepared from fermented peanut meal

To study the influence of degree of hydrolysis (DH) on antioxidant properties of peanut peptides, the peanut meal was fermented by Bacillus subtilis. The fermentation time was 48, 72, and 96 h, respectively, to prepare peanut peptides at different degree of hydrolysis. The peanut peptides (11.18, 16.20, and 21.41% of DH, respectively) were extracted from fermentation liquid. The antioxidant properties of these peanut peptides were evaluated based on DPPH^· radical (1,1-Diphenyl-2-picrylhydrazyl radical) scavenging activity, superoxide anion-scavenging activity, reducing power, metal-chelating activity, and inhibition of linoleic acid autooxidation. Peanut peptides (21.41% of DH) at 1 mg/mL exhibited 80.86 and 29.35% of scavenging concentration percent on DPPH^· and superoxide anion radical, respectively. In addition, the reducing power of peanut peptides was 0.368 at 2 mg/mL, and they possessed 76.32% of Fe²⁺-chelation ability at 2 mg/mL and 63.75% of inhibition of linoleic acid autooxidation at 0.8 mg/mL. The antioxidant activities of the peanut peptides (21.41% of DH) were stronger compared with others (11.18 and 16.20% of DH), and this indicated the antioxidant activities of peanut peptides increased with increasing DH (p < 0.05). To know much about the peanut peptides, they were subjected to amino acid analysis and determination of molecular weight distribution. Some acidic amino acids and essential amino acids were found, and the average molecular weight distributions were concentrated in <1,400 Da (86.96%). Combined with the results of the amino acid profiles, the peanut peptides were believed to have high nutritive value besides antioxidant activities.     

Purification,characterization, and in vitro digestion of novel antioxidant peptides from chicken blood hemoglobin

The study aimed to purify and characterize antioxidant peptides from chicken blood hemoglobin hydrolysate. The fraction M₂ (< 3 KDa) with the strongest antioxidant activity was isolated by ultrafiltration, and its DPPH (1,1-diphenyl-2-picryl-hydrazyl radical) free radical scavenging rate, ABTS [2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulphonate)] free radical scavenging rate, and iron ion chelation activity were 82.91%, 77.49%, and 80.99%, respectively. After in vitro digestion, the antioxidant capacity of chicken blood hydrolysate was significantly higher than that before digestion (p < 0.05). M₂ exhibited the strongest antioxidant activity after stomach digestion, with a DPPH radical scavenging rate and iron ion chelating power of 82.91% and 79.61%, respectively. Component A was purified from M₂ by Sephadex G-25 gel chromatography. The peptide sequences were identified by LC-MS/MS from fraction A, and four peptides, AEDKKLIQ (944.54 Da), APAPAAK (625.36 Da), LSDLHAHKL (1033.57 Da), and LSNLHAYNL (1044.54 Da) were synthesized using the solid-phase peptide method, among which APAPAAK was a novel antioxidant peptide. Molecular docking was used to simulate the binding of these four peptides to the key active site of Keap1 via hydrogen bonding. This study suggests that chicken blood may provide a new natural source of antioxidant peptides.     

Antioxidant peptides obtained from goose egg white proteins by enzymatic hydrolysis

In this study, antioxidant peptides from goose egg white proteins produced using various enzymes were purified and characterised. Two peptides were named as p14 and p16, showing the highest scavenging activity of 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical and the highest metal ion chelating activity, respectively. The sequences of p14 and p16 were identified to be STMMEERRMKVY (1560.72 Da) and DVFRELRVQ (1161.62 Da), respectively. The sequence of p14 has a similarity of 75% to ovalbumin from Meleagris gallopavo and the sequence of p16 has a similarity of 67% to ovalbumin from Taeniopygia guttata. IC₅₀ values of p14 and p16 were determined, and results showed that DPPH radical scavenging activity was 81.6 and 205.5 μm , 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonicacid)(ABTS) radical scavenging was 88.4 and 153.8 μm , hydroxyl radical scavenging was 85.5 and 116.3 μm and metal ion chelating was 170.6 and 117.9 μm , respectively. The two identified peptides from goose egg white hydrolysates act as potent natural antioxidant agents.     

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.     

Isolation and identification of antioxidative peptides from rice endosperm protein enzymatic hydrolysate by consecutive chromatography and MALDI-TOF/TOF MS/MS

The defatted rice endosperm protein (REP) was, respectively, digested by five different protease treatments (Alcalase, Chymotrypsin, Neutrase, Papain and Flavorase), and Neutrase appears to be the most desirable for producing high quality antioxidant peptides from REP. Specially, the DPPH and hydroxyl radical scavenging activities of NHREP were higher than its superoxide radical scavenging activity, and the percentage inhibition of autooxidation of NHREP (80.09%) was similar to that of α-tocopherol (86.59%) on day 5. Furthermore, NHREP was purified consecutively, and the antioxidant peptides were identified to be Phe-Arg-Asp-Glu-His-Lys-Lys (FRDEHKK, 959.5 Da) and Lys-His-Asp-Arg-Gly-Asp-Glu-Phe (1002.5 Da) by MALDI-TOF/TOF MS/MS. Lastly, FRDEHKK was chemically synthesised. It significantly inhibited lipid peroxidation in an linoleic acid emulsion system more effectively than α-tocopherol, and enhanced the viability of t-BHP induced cytotoxicity up to 74.38% (for MRC-5) and 78.39% (for RAW264.7) at 80 μg/ml. Conclusively, it was feasible to produce natural antioxidants from REP.     

Evaluation of Antioxidant Activities of Zein Protein Fractions

Zein protein was extracted from the by‐product corn gluten meal. The obtained zein protein was 1st hydrolyzed by 4 different proteases. The antioxidant activities of the hydrolysates or peptides were evaluated by free radical scavenging activity, metal ion chelating activity, and lipid peroxidation inhibitory capacity. Among hydrolysates produced, alkaline protease hydrolysates exhibited the highest antioxidant activity. A regression model was established by uniform design to optimize the alkaline protease hydrolysis conditions. The hydrolysates with molecular weight < 3 kDa obtained from ultrafiltration showed the highest antioxidant activities in all relevant assays. The hydrolysates with molecular weight <3 kDa were subsequently purified by gel filtration chromatography, and fraction F3 exhibited the highest antioxidant activities. Two peptides were identified from fraction F3 using LC‐ESI‐Q‐TOF MS/MS as Pro‐Phe (263.13 Da) and Leu‐Pro‐Phe (375.46 Da). These peptides exhibited good free radical scavenging activity and lipid peroxidation inhibitory effect. The results clearly indicated that zein protein fractions are good sources for the development of natural antioxidants for the food industry.     

Purification and identification of antioxidant peptides from corn gluten meal

Corn gluten meal was hydrolyzed by alkaline protease and Flavourzyme to obtain the antioxidant peptides. The antioxidant activities of the hydrolysates or peptides were evaluated by free radical scavenging capacity (1,1-diphenyl-2-picrylhydrazyl/2,2-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt/hydroxyl radical/superoxide radical anion), metal ion (Fe²⁺/Cu²⁺) chelating activity and lipid peroxidation inhibitory capacity. The hydrolysates were separated by ultrafiltration, and those with molecular weight <10 kDa exhibited highest antioxidant activity in all relevant assays. The hydrolysates were subsequently purified by gel filtration chromatography, and fraction F3 showed the highest antioxidant activity. Three peptides were identified from fraction F3 using LC–ESI–Q–TOF MS/MS as Leu-Pro-Phe (375.46 Da), Leu-Leu-Pro-Phe (488.64 Da) and Phe-Leu-Pro-Phe (522.64 Da). These peptides exhibited good free radical scavenging activity and lipid peroxidation inhibitory effect. Thus, corn gluten meal may be used as a potential source of antioxidant peptides for food and nutraceutical applications.     

Antioxidant and anti‐acetylcholinesterase activities of anchovy (Coilia mystus) protein hydrolysates and their memory‐improving effects on scopolamine‐induced amnesia mice

Anchovy protein hydrolysates (APHs) were prepared through hydrolysis for 2, 4 or 8 h (APH‐2, APH‐4 and APH‐8, respectively). The chemical analyses, in vitro assessments [antioxidant activity and acetylcholinesterase (AchE) inhibitory activity] and in vivo mice tests were evaluated. Results revealed that APH‐8 exhibited the strongest reducing power and AchE inhibitory capacity (IC₅₀ = 159.76 ± 0.03 mg mL^?1), which may be due to its specific amino acid composition and newly formed peptides. In addition, AchE inhibitory kinetics of amino acids suggested that lysine was featured of both competitive and noncompetitive inhibitors. Furthermore, the results of in vivo study showed that all APHs exhibited memory‐improving action on scopolamine‐induced amnesia mice especially, APH‐8, indicating that anchovy protein is a potential source for health‐promoting peptides.     

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.     

Transglutaminase cross-linking effect on sensory characteristics and antioxidant activities of Maillard reaction products from soybean protein hydrolysates

To improve the yield of Maillard peptides, a microbial transglutaminase (MTGase) was used to increase the content of 1000–5000 Da peptides in soybean protein hydrolysates by using a cross-linking reaction. The sensory characteristics and antioxidant activities of corresponding Maillard Reaction Products (MSPC) was then evaluated. After cross-linking treatment the content of 1000–5000 Da peptides in protein hydrolysates and the yield of Maillard peptides increased by 21.19% and 8.71%, respectively, which contributed to the improved mouthfulness of MSPC. The bitter amino acids were significantly decreased and the umami acids were markedly increased in MSPC. Volatile compounds identified by GC–MS analysis showed that the content of the important meaty flavour compounds (such as 2-methyl-3-furanthiol, bis(2-methyl-3-furyl)disulfide) of MSPC were dramatically higher than that of MRPs from uncross-linking peptides. Combined with sensory evalution, it was confirmed that MTGase cross-linking improved the flavour Characteristics and did not affect the antioxidant activity of MSPC.     

Fractionation and purification of antioxidant peptides from abalone viscera by a combination of Sephadex G-15 and Toyopearl HW-40F chromatography

Abalone viscera, a protein-rich by-products from the abalone processing industry, are normally discarded as wastes. In the present study, four different proteases were used to hydrolyse abalone viscera to prepare high-activity antioxidant peptides, and their hydrolysis effects were compared. Although the hydrolytic abilities of papain and trypsin were inferior to the alcalase and neutrase, their use resulted in significantly (P < 0.05) higher scavenging activities for DPPH. The hydrolysates mainly consisted of peptides with a molecular weight <3 kDa, and the fractionation was achieved using a combination of Sephadex G-15 and Toyopearl HW-40F gel filtration chromatography, which overcomes the disadvantages of traditional membrane separation technology in fractionating peptides with relatively similar molecular weight distribution. The DPPH scavenging activities of the components containing peptides <1 kDa (fractions E) were significantly (P < 0.01) higher than those containing peptides >1 kDa. The different fractions E were further purified by reversed-phase high-performance liquid chromatography, and a total of 16 target peptides, containing 4-8 amino acids, enriched in hydrophobic amino acids and C-terminal Arg, with molecular weights ranging from 500 to 850 Da, were identified.     

Antioxidant activities of the rice endosperm protein hydrolysate: identification of the active peptide

The defatted rice endosperm protein (REP) was digested using five different proteases (Alcalase, Chymotrypsin, Neutrase, Papain, and Flavorase) to produce the antioxidative peptide. The degree of hydrolysis of REP by Neutrase (20.00%) was slightly lower than that of Chymotrypsin, but higher than those of other enzymes. The Neutrase hydrolysate from rice endosperm protein (NHREP) took on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity similar to α-tocopherol. Also, the reaction condition of Neutrase hydrolysis was moderate (pH of 7.0 and temperature of 37 °C). Therefore, Neutrase was chosen to be the optimum enzyme for producing the antioxidative peptide from REP. In succession, the antioxidant activities of NHREP were further evaluated. The median effective concentration (EC₅₀) value of NHREP for hydroxyl radical scavenging activity was 2.0 mg/mL, while its superoxide radical scavenging activity did not surpassed 50% even at 6 mg/mL. The percentage inhibition of autooxidation in linoleic acid system by NHREP was 82.09%, similar to that of α-tocopherol (86.59%) on day 5 at the same concentration. NHREP displayed 89.15% chelating effect on ferrous ion at a concentration of 1000 μg/mL, and a high correlation was also observed between the reducing power and antioxidant activity of NHREP (r ² = 0.99678). Consequently, NHREP was purified and identified, and the sequence determination by MALDI-TOF/TOF MS/MS revealed that the active constituent contained eight amino acids in its sequence (Lys-His-Asn-Arg-Gly-Asp-Glu-Phe), with the molecular mass of 1002.5217 Da. After sequence interpretation and database searching, the MS/MS spectrum was matched to glutelin protein f (460–465).     

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.     

Stability of antioxidant peptides from duck meat after post‐mortem ageing

The stability of antioxidant peptides from aged duck meat during processing and simulated gastrointestinal digestion was investigated. The antioxidant peptides preserved a high stability in the presence of diverse NaCl or upon various time heating. The antioxidant activities were strengthened by the addition of 4–8% glucose or by heating at 100 °C, whereas they were lost under alkaline conditions. During in vitro digestion, the antioxidant activities increased with pepsin treatment but then decreased following trypsin digestion. Pepsin hydrolysed peptides into short fragments and results in the increased exposure of internal hydrophobic amino acids. With further treatment by trypsin, peptides can be hydrolysed completely and more free amino acids were released, leading to the decline in surface hydrophobicity. These variations might be responsible for the change in antioxidant activity during in vitro digestion. The antioxidant peptides from aged duck with high stability can be used as functional food ingredients to improve human health.