Utilization of cooking juice of young tuna processed into canned tuna as condiments: Effect of enzymatic hydrolysis and membrane treatment

Tuna cooking juice containing approximately 4% solubilized proteins was collected and hydrolyzed by two commercial enzymes, Orientase (O-R) and Protease XIII (A-O). To separate and concentrate the protein hydrolysate, ultrafiltration (UF) and reverse osmosis (RO) were used. Results indicated that the active enzyme A-O displayed greater quantities Vmax/Km than O-R. After 5h of incubation at 50°C with a ratio of substrate: enzyme=25: 1 v/v the degree of protein hydrolysis in tuna cooking juice was approximately 32%, and total free amino acid contents of the cooking juice hydrolysates were 6.80 (O-R) and 8.33 (A-O) mmol/100 mL. After UF via an AF-30-1812-T cartridge equipped with a molecular weight cut-off (MWCO) of 10 kDa, the enzyme active residues in retentate were 20.59 and 19.89%, and the total free and essential amino acids of the permeate were 7.01, 3.75 and 6.77, 3.27 mmol/100 mL for O-R and A-O, respectively. The hydrolysates mainly consisted of peptides less than 2kDa according to gel filtration. Sensory evaluation of concentrated hydrolysates through RO confirmed that aroma, umami taste and overall quality of the hydrolysates were suitable as a condiment.