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Summary To assess the antioxidant properties of fish protein hydrolysate from giant kingfish Caranx ignobilis (Forsskal, 1775), muscle and skin were obtained using various proteases (papain, pepsin, trypsin and α-chymotrypsin), respectively. Antioxidant activities of the resulting hydrolysates were evaluated using 2, 2-diphenyl-1-picrylhydrazyl radical scavenging activity, reducing power and metal chelating activity. Among the hydrolysates, peptic of muscle (37 ± 1.0; 0.290 ± 0.012; 63.30 ± 0.57) and tryptic of skin (36.2 ± 1.0; 0.190 ± 0.110; 63 ± 0.57) hydrolysates, which had the highest free radical scavenging activity, was subjected to purification using Sephadex G-25. The fractionated hydrolysates were superior to the original hydrolysates in the antioxidative activity tested. The active fractions (MF2 and SF2) effectively inhibited lipid peroxidation in linoleic acid emulsion system, and the activity was compared with α-tocopherol. The amino acid profile of MF2 and SF2 showed a high level of essential amino acids, and the most abundant amino acids were in the order His (12.01% and 7.08%), Phe (7.05% and 6.18%) and Lys (6.76% and 4.74%). Conclusively, C. ignobilis muscle and skin hydrolysates could be a promising rich source of natural antioxidants.

Summary In our present investigation, Nemipterus japonicus and Exocoetus volitans backbone protein were hydrolysed by proteases like trypsin and pepsin, respectively. The protein hydrolysates were purified by different chromatographic methods, and the resulted purified peptides were analysed for their amino acid sequences by electrospray ionisation–MS/MS. The analysis of peptides showed sequences as Gly-His-Met-Ser (451.8 Da) and Leu-Glu-Val-Lys-Pro (596.9 Da) for N. japonicus and E. volitans muscle, respectively. The presence of hydrophobic amino acids contributes more to the antioxidant activities of peptides than other amino acids. Moreover, sequence of amino acids in peptides plays an important role in their antioxidant activities.

Summary 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.