Abstract: Quality changes of smoked skipjack tuna processing byproduct during enzymatic hydrolysis under optimized conditions (trypsin to flavourzyme activity, 2:1; and total enzyme dosage, 3 000 U/g) were analyzed. The results showed that the degree of hydrolysis (DH) kept increasing during 30 h hydrolysis. Sensory evaluation showed that the hydrolysates had a favorable sensory score within 10 h, and then began to fall sharply. The content of TVB-N increased slowly during the first 10 h and then increased sharply. The nitrogen solubility index kept rising during the first 20 h and then increased slightly. Free amino acid content gradually increased during the entire hydrolysis process, but increased slower from 20 h onwards. Glutamic acid, giving a relatively higher TAV value and umami taste, contributed most to the overall taste of the hydrolysates. Although they continuously decreased as the reaction time extended, phenols and aldehydes made significant contribution to the flavor of the hydrolysates, especially the latter, which had a higher relative odor activity value (ROAV). The results of the present study is useful for the preparation of high-quality smoked skipjack tuna hydrolysate with good flavor, and could also provide a theoretical basis for further development of related seafood seasoning products.

Key words: smoked skipjack tuna, mixed enzyme hydrolysis, sensory evaluation, free amino acid, volatile flavor, quality variation