Use of Plastein Reaction in Recovering Protein from Fish Waste

A high quality proteinaceous product is recoverable in 35% yield from fish waste by a process of peptic hydrolysis followed by a pepsin-catalyzed recombination of soluble peptides to form plastein. Hydrolysis is at pH 2.0 and 37 C for 6 hr. Soluble peptides are then separated from insoluble residue, adjusted to pH 4.5, concentrated at 45 C to 30% protein solids, and incubated for 24 hr at 37 C with additional pepsin. The insoluble plastein formed during incubation is filtered, washed, and dried. In a pilot experiment with fillet waste from Petrale sole (Eopsetta jordani), the yield was 35% of total original protein. Proximate composition of the product was: protein, 96.1%; moisture, 2.9%; ash, 0.5%; and lipid, 0.0%. The plastein contained a higher proportion of essential amino acids than did a hydrolysate of the whole waste, all except tryptophan exceeding FAO reference standards.