Abstract: The enzymatic hydrolysis of oysters with Protamex was optimized using one-factor-at-a-time and orthogonal array design methods. The independent variables were hydrolysis time, enzyme dosage and temperature, and the response was degree of hydrolysis. The solubility characteristics of oyster hydrolysates were evaluated by nitrogen solubility index (NSI), trichloroacetic acid-nitrogen solubility index (TCA-NSI), and the amino acid score (AAS), chemical score (CS) and essential amino acid index (EAAI) were measured for nutritional quality evaluation. The optimal hydrolysis parameters were determined as follows: enzyme dosage, 30 AU/kg; temperature, 55 ℃; and time, 4 h, yielding a degree of hydrolysis of up to 27.28%. The obtained hydrolysate contained 18 amino acids, being high in umami amino acids, with Glu being the most abundant and essential amino acids accounting for 39.5% of the total amino acids, suggesting high nutritional value. At pH 4.0–7.0, the NSI of the hydrolsate was over 83%, and TCA-NSI was as high as 88.64% indicating good solubility.

Key words: oyster, Protamex, degree of hydrolysis, nitrogen solubility index, nutritional evaluation