Studies on Protease from the Digestive Tract of Tiger Shrimp: Production of fish protein concentrate through plastein reaction

抄録

A protease from the digestive tract of tiger shrimp has been partially purified by means of organic solvent extraction and ammonium sulphate fractionation. The enzyme was capable to produce a protein-like material, called plastein, obtained from plastein reaction with substrate (hydrolysate) from autolyzed product of tiger shrimp digestive tract. The plastein and hydrolysate had relatively high protein content and also a respective amino acid composition. The amino acid compositions of protein hydrolysate were aspartic acid (13.3%), glutamic acid (13.8%), glycine (10.9%), histidine (14.0%), tyrosine (10.6%), methionine (4.5%), isoleucine (4.7%), phenylalanine (22.5%), and lysine (15.8%). The amino acid compositions of plastein products of native enzyme were glutamic acid (3.2%), serine (6.5%), glycine (10.0%), histidine (8.2%), methionine (17.8%), isoleucine (11.2%), phenylalanine (14.9%), and lysine (14.9%). The amino acid compositions of plastein products of immobilized enzyme were aspartic acid (14.1%), glutamic acid (12.4%), histidine (6.9%), tyrosine (8.4%), methionine (8.3%), leucine (10.5%), glycine (13.5%), and lysine (25.7%). The content of phenylalanine, an amino acid considered as the cause of a bitter taste of peptide (protein), decreased through plastein reaction from 22.5% for protein hydrolysate to 14.9% for plastein product of native enzyme. Moreover, the phenylalanine content of plastein product of immobilized enzyme became extremely low (undetected). In general, the products have a potential nutritional value. It may be used for nutritional supplements in various formulated food/feed products.