The role of molecular size in antioxidant activity of peptide fractions from Pacific hake (Merluccius productus) hydrolysates

Identification of bioactive peptide from Oreochromis niloticus skin gelatin

Fish skin, one type of wastes generated from Nile tilapia processing, is still a good source of collagen and gelatin. Bioactive peptides can be obtained from Nile tilapia skin gelatin by trypsin digestion. Trypsin hydrolysate was subsequently purified by gel filtration chromatography. Trypsin A fraction showed the greatest reducing power (5.138 ± 1.060 μM trolox/mg peptide) among all hydrolysate fractions, while trypsin B fraction from gel filtration column was found to exhibit the best radical scavenging and angiotensin-I-converting enzyme (ACE) inhibitory activities 8.16 ± 2.18 μg trolox/mg peptide and 59.32 ± 9.97 % inhibition, respectively. The most active fraction was subjected to MALDI-TOF/TOF MS/MS. After annotation by Mascot sequence matching software (Matrix Science) with Ludwig NR Database, two peptide sequences were identified; GPEGPAGAR (MW 810.87 Da) and GETGPAGPAGAAGPAGPR (MW 1490.61 Da). The docking analysis suggested that the shape of the shorter peptide may be slightly more proper, to fit into the binding cleft of the ACE. However, the binding affinities calculated from the docking showed no significant difference between the two peptides. In good agreement with the in silico data, results from the in vitro ACE inhibitory activity with synthetic peptides also showed no significant difference. Both peptides are thus interesting novel candidates suitable for further development as ACE inhibitory and antioxidant agents from the natural source.

Overview of Antioxidant Peptides Derived from Marine Resources: The Sources, Characteristic, Purification, and Evaluation Methods

Marine organisms are rich sources of structurally diverse bioactive nitrogenous components. In recent years, numerous bioactive peptides have been identified in a range of marine protein resources, such as antioxidant peptides. Many studies have approved that marine antioxidant peptides have a positive effect on human health and the food industry. Antioxidant activity of peptides can be attributed to free radicals scavenging, inhibition of lipid peroxidation, and metal ion chelating. Moreover, it has also been verified that peptide structure and its amino acid sequence can mainly affect its antioxidant properties. The aim of this review is to summarize kinds of antioxidant peptides from various marine resources. Additionally, the relationship between structure and antioxidant activities of peptides is discussed in this paper. Finally, current technologies used in the preparation, purification, and evaluation of marine-derived antioxidant peptides are also reviewed.

Antioxidant activity and functional properties of enzymatic protein hydrolysates from common carp (Cyprinus carpio) roe (egg)

Previously, we have reported the composition, molecular mass distribution and in vivo immunomodulatory effects of common carp roe protein hydrolysates. In the current study, antioxidative activity and functional properties of common carp (Cyprinus carpio) roe (egg) protein hydrolysates, prepared by pepsin, trypsin and Alcalase, were evaluated. The three hydrolysates showed excellent antioxidant activities in a dose dependent manner in various in vitro models such as 2,2 diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2'-azino-bis(3-ethylbenzthiazoline-6)-sulfonic acid (ABTS(+)) radical scavenging activity, ferric reducing antioxidant power (FRAP) and ferrous ion (Fe(2+)) chelating ability. Enzymatic hydrolysis significantly increased protein solubility of the hydrolysates to above 62 % over a wide pH range (2-12). Carp roe hydrolysates exhibited good foaming and emulsification properties. The results suggest that bioactive carp roe protein hydrolysates (CRPHs) with good functional properties could be useful in health food/nutraceutical/pharmaceutical industry for various applications.

Chemical and cellular antioxidative properties of threadfin bream (Nemipterus spp.) surimi byproduct hydrolysates fractionated by ultrafiltration

Protein hydrolysate from frame, bone and skin (FBSH) of threadfin bream was prepared using Virgibacillus sp. SK33 proteinase and fractionated using sequential ultrafiltration membranes with molecular weight cut-offs (MWCO) of 30, 5 and 1 kDa, respectively. Four fractions, namely FBSH-I (>30 kDa), FBSH-II (5-30 kDa), FBSH-III (1-5 kDa), and FBSH-IV (<1 kDa), were obtained. All fractions were rich in Lys, Glu/Gln, Gly, Pro, Ala, Asp/Asn, and Arg. FBSH-III and FBSH-IV showed the highest surface hydrophobicity measured by 8-anilino-1-naphthalenesulfonic acid (ANS) probe (p<0.05). FBSH-III showed the highest antioxidant activity and cytoprotective effects against tert-butyl hydroperoxide (TBHP)-induced cytotoxicity of Caco-2 cells. In addition, FBSH-III inhibited lactate dehydrogenase (LDH) leakage and intracellular reactive species (ROS) production in a dose-dependent manner. FBSH-III retained antioxidant activity and cytoprotective capacity after in vitro simulated gastrointestinal digestion. These results suggested that FBSH-III might potentially be nutraceutical peptides with antioxidative properties.

Influence of enzymatic hydrolysis and enzyme type on the nutritional and antioxidant properties of pumpkin meal hydrolysates

Nutritional and antioxidant properties of pumpkin meal and their hydrolysates prepared by hydrolysis with alcalase, flavourzyme, protamex or neutrase were evaluated. The hydrolysis process significantly increased protein content from 67.07% to 92.22%. All the essential amino acids met the Food and Agriculture Organization of United Nations/World Health Organization (WHO/FAO) suggested requirements for children and adults. The amino acid score (AAS) of meal was increased from 65.59 to 73.00 except for flavourzyme (62.97) and protamex (62.50). The Biological Value (BV) was increased from 53.18 to 83.44 except for protamex (40.97). However hydrolysis decreased the Essential Amino Acid/Total Amino Acid ratio (EAA/TAA) from 32.98% to 29.43%. Protein Efficiency Ratio (PER) was comparable to that of good quality protein (1.5) except for flavourzyme hydrolysate which had PER1 = 0.92, PER2 = 1.03, PER3 = 0.38. The in vitro protein digestibility (IVPD) increased from 71.32% to 77.96%. Antioxidant activity increased in a dose-dependent manner. At 10 mg mL(-1), the hydrolysates had increased 1,1-diphenyl-2-picrylhydrazy (DPPH) radical scavenging activities from 21.89% to 85.27%, the reducing power increased from Abs(700nm) 0.21 to 0.48. Metal (Iron) chelating ability was improved from 30.50% to 80.03% at 1 mg mL(-1). Hydrolysates also showed better capabilities to suppress or delay lipid peroxidation in a linoleic acid model system. Different proteases lead to different Degrees of Hydrolysis (DH), molecular weight (MW) distribution, amino acid composition and sequence, which influenced the nutritional properties and antioxidant activities of the hydrolysates. Alcalase was the most promising protease in production of pumpkin protein hydrolysates with improved nutritional quality, while flavourzyme was best in production of hydrolysates with improved antioxidative activity among various assays. These results showed that hydrolysates from by-products of pumpkin oil-processing might serve as alternative sources of dietary proteins with good nutritional quality, and protection against oxidative damage.

The effect of thermal and ultrasonic treatment on amino acid composition, radical scavenging and reducing potential of hydrolysates obtained from simulated gastrointestinal digestion of cowpea proteins

The effect of thermal and ultrasonic treatment of cowpea proteins (CP) on amino acid composition, radical scavenging and reducing potential of hydrolysates (CPH) obtained from in vitro simulated gastrointestinal digestion of CP was evaluated. Hydrolysis of native and treated CP with gastrointestinal pepsin and pancreatin yielded CPH that displayed antioxidant activities based on oxygen radical scavenging capacity (ORAC), ferric reducing antioxidant power (FRAP) and superoxide radical scavenging activity (SRSA). CPH derived from the treated CP yielded higher ORAC values than CPH from untreated proteins. However, lower significant FRAP and SRSA values were observed for these samples compared to untreated CPH (p < 0.05). Amino acid analysis indicated that CP processing decreased total sulphur-containing amino acids in the hydrolysates, particularly cysteine. The amount of cysteine appeared to be positively related to FRAP and SRSA values of CPH samples, but not ORAC. The results indicated that thermal and ultrasonic processing of CP can reduce the radical scavenging and reducing potential of the enzymatic hydrolysates possibly due to the decreased amounts of cysteine. Since the hydrolysates were generated with gastrointestinal enzymes, it is possible that the resulting compounds are produced to exert some health functions during normal consumption of cowpea.

Purification and identification of antioxidant peptides from enzymatic hydrolysates of Tilapia (Oreochromis niloticus) frame protein

Tilapia frame protein was hydrolyzed by different proteases, including properase E, pepsin, trypsin, flavourzyme, neutrase, gc106 and papain, to obtain antioxidant peptides. The tilapia frame protein hydrolysate (TFPH) obtained by trypsin exhibited the highest degree of hydrolysis and antioxidant activity. Three series of peptides (TFPH1, TFPH 2 and TFPH 3) were obtained by ultrafiltration of TFPH through molecular weight cut-off membranes of 5, 3 and 1 kDa, respectively, and their IC₅₀ values on scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, superoxide anion radical (^•O₂), hydrogen peroxides (H₂O₂) and hydroxyl radical (•OH) activities were determined and compared with glutathione (GSH). The results showed that TFPH1 had the highest antioxidant activity. TFPH1 was further purified using ion exchange chromatography, gel filtration chromatography, and reversed phase high performance liquid chromatography (RP-HPLC). Finally, two antioxidant peptides were identified and the amino acid sequences were identified as Asp-Cys-Gly-Tyr (456.12 Da) and Asn-Tyr-Asp-Glu-Tyr (702.26 Da), respectively. The IC₅₀ values of two peptides on hydroxyl radical scavenging activity were 27.6 and 38.4 μg/mL, respectively.

Preparation and evaluation of antioxidant peptides from ethanol-soluble proteins hydrolysate of Sphyrna lewini muscle

To get high yield of ethanol-soluble proteins (EP) and the antioxidant peptides from Sphyrna lewini muscle, orthogonal experiments (L(9)(3)(4)) were applied to optimize the best extraction conditions and enzyme hydrolysis conditions. The yield of EP reached 5.903±0.053% under the optimum conditions of ethanol concentration 90%, solvent to material ratio 20:1, extraction temperature of 40°C and extraction time of 80min. The antioxidant SEPH (EP hydrolysate of S. lewini muscle) was prepared by using papain under the optimum conditions of enzymolysis time 2h, total enzyme dose 1.2%, enzymolysis temperature 50°C and pH 6, and its DPPH radical scavenging activity reached 21.76±0.42% at the concentration of 10mg/ml. Two peptides (F42-3 and F42-5) were isolated from SEPH by using ultrafiltration, anion-exchange chromatography, gel filtration chromatography and RP-HPLC. The structures of F42-3 and F42-5 were identified as Trp-Asp-Arg and Pro-Tyr-Phe-Asn-Lys with molecular weights of 475.50Da and 667.77Da, respectively. F42-3 and F42-5 exhibited good scavenging activity on hydroxyl radical (EC(50) 0.15mg/ml and 0.24mg/ml), ABTS radical (EC(50) 0.34mg/ml and 0.12mg/ml), and superoxide anion radical (EC(50) 0.09mg/ml and 0.11mg/ml), but moderate DPPH radical (EC(50) 3.63mg/ml and 4.11mg/ml). F42-3 and F42-5 were also effectively against lipid peroxidation in the model system and peroxyl free radical scavenging in β-carotene linoleic acid assay. Their high activities were due to the smaller size and the presence of antioxidative amino acids within the peptide sequences.