Indian mackerel (Rastrelliger kanagurta), a species of Scombridae family, has a high content of dark muscle resulting in difficulties in making high-quality surimi from it. However, Indian mackerel muscle could be used for the production of value-added products such as protein hydrolysate. Enzymatic hydrolysis could be applied to improve and upgrade the functional and nutritional properties of fish proteins. Trypsin (EC 3.4.21.4) is a serine proteinase that specifically hydrolyzes peptide chains at the carboxyl side of arginine and lysine residues. It plays a key role in the food industry, e.g. in the production of protein hydrolysates, meat flavorants and culture media. This enzyme has been isolated from the viscera of various fish such as Unicorn leatherjacket (Aluterus monoceros) used for fillet production in Thailand, especially for export as frozen fillets. As a consequence, large amounts of viscera have been produced as by-products and are an important source for isolation of proteolytic enzymes, especially trypsin. In this study trypsin from unicorn leatherjacket pyloric caeca was used for production of protein hydrolysate with antioxidative activity from Indian mackerel muscle. Trypsin was purified by ammonium sulfate precipitation and soybean trypsin inhibitor (SBTI)–Sepharose 4B affinity chromatography from the pyloric caeca of unicorn leatherjacket and hydrolysate from Indian mackerel muscle with different degrees of hydrolysis (20, 30 and 40% DH) was prepared using the purified trypsin and antioxidative activities (DPPH: 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activity; ABTS: 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical-scavenging activity; FRAP: ferric-reducing antioxidant power and ferrous-chelating activity) of the hydrolysate were determined. The results showed antioxidative activities of the hydrolysate from Indian mackerel muscle increased with increasing DH up to 40% (P <0.05) (Figure 1 ).
