Abstract:

Objective: To investigate the optimum parameters for enzymatic hydrolysis of collagen-rich waste liquid from
squid (Dosidicus gigas) tentacle peeling and evaluate the antioxidant activity of its hydrolysate. Methods: The hydrolysis
parameters were optimized using one-factor-at-a-time method and response surface methodology based on 1,1-diphenyl-2-
picrylhydrazyl (DPPH) radical scavenging activity and degree of hydrolysis (DH). The antioxidant activity of hydrolysate
was evaluated by using scavenging rate of 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt radical
(ABTS+·) and hydroxyl radical scavenging and ferric reducing/antioxidant power (FRAP) assays and the molecular weight
distribution was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration
chromatography. Results: The optimal hydrolysis parameters were determined as follows: hydrolysis temperature, 50 ℃;
substrate (protein) content, 3.2%; hydrolysis time, 3.7 h; enzyme dosage, 3 000 U/g; and initial pH, 7.4, resulting in a DH
value of (37.23 ± 0.08) % and a scavenging rate of DPPH radical of (43.61 ± 0.09) %, respectively. The half inhibitory
concentrations for ABTS+· and hydroxyl radical scavenging ability (IC50) of the hydrolysate obtained were 0.37 and
0.41 mg/mL, respectively. Moreover, the product showed a strong reducing capacity. SDS-PAGE analysis showed that most
collagens in the waste liquid were hydrolyzed into small peptides with molecular weight of 1?5 kD as determined by gel
exclusion chromatography. Conclusion: The hydrolysate derived from waste liquid from squid tentacles peeling has strong antioxidant
activity and could be used as a functional seafood condiment and nutritional supplement for further development and utilization.

Key words: waste liquid from squid tentacle peeling, enzymatic hydrolysis, antioxidant activity, degree of hydrolysis, half inhibitory concentration