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 5 h 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 2 kDa 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.
