Effect of Degree of Hydrolysis on Biochemical Properties and Biological Activities (antioxidant and Antihypertensive) of Protein Hydrolysates from Pacific Thread Herring (ophistonema Libertate) Stickwater

High amounts of rich-protein liquid wastes are produced during seafood processing. The effluent called stickwater resulting from the processing of Pacific thread herring (Ophistonema libertate) into fishmeal, was evaluated as protein source to produce bioactive protein hydrolysates by using Alcalase as enzyme source. The effect of degree of hydrolysis on biochemical properties (proximate analysis, molecular weight, and amino acid composition) and antioxidant and antihypertensive activities of stickwater protein hydrolysates obtained with Alcalase was determined. Degree of hydrolysis (DH) of samples (5%, 10%, 15% and 20%) influences its biochemical and bioactive properties. The maximum ABTS and FRAP activity values (P < 0.05) were exhibited by hydrolysates at 15% DH (EC50 = 2.8 mg/mL and TEAC = 1.16 ± 0.03 mM TE/mg, respectively). Whereas the highest DPPH scavenging activity (P < 0.05) was found for hydrolysates at 5 % and 10 % of DH (EC50 = 34.7 mg/mL and 37 mg/mL respectively). Furthermore, enzymatic hydrolysis enhanced angiotensin converting enzyme (ACE)-inhibitory activity, being those at 5 and 10% of DH, which exhibited lower IC50 values (P < 0.05) compared to non-hydrolyzed stickwater. Peptide distribution of protein hydrolysates at < 1.35 kDa was in a range of 47–62% of total peptides and the presence of amino acids related to antioxidant activity such as His, Lys, Met, Tau, Tyr and Trp was detected in stickwater and protein hydrolysates. The production of protein hydrolysates from Pacific thread herring stickwater, represents an alternative to obtain added-value products with potential antioxidant and antihypertensive activity.