Abstract
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.
Highlights
About 87 percent of the 179 million metric tons of fish produced in 2018 was used for direct human consumption, a share that has increased in recent decades
Peptide distribution of protein hydrolysates at < 1.35 kDa was in a range of 47 to 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 monitoring of the degree of hydrolysis over time showed an initially high hydrolysis rate, reaching Degree of hydrolysis (DH) values of 5% and 10% within three minutes (0.45 and 2.6 minutes, respectively; Fig. 1).This was followed by a decreased hydrolysis rate, reaching 15% DH at 35.7 minutes and 20% DH at 223 minutes. This decelerated hydrolysis rate over time to reach a stationary phase has been related to the substrate depletion in the enzyme mixture and the potentially adverse effect of reaction products, which might saturate the active site of the enzyme and inhibit its catalytic mechanisms [26,27]
Summary
About 87 percent (over 156 million metric tons) of the 179 million metric tons of fish produced in 2018 was used for direct human consumption, a share that has increased in recent decades. Most of the remaining 13 percent (about 22 million metric tons) was used to produce fishmeal and fish oil. Considerable amounts of solid and liquid (effluents) wastes and byproducts are produced during seafood processing (e.g., trimming, eviscerating, peeling, or shelling) [1]. Industrial fishery effluents are generated during operations such as washing, thawing, and cooking, but during fishmeal production [2]. Fishmeal processing comprises several steps, such as mincing, cooking, pressing, and drying of whole fish. After raw materials are cooked and pressed, solid (press cake) and liquid (press liquor) phases are obtained. The press liquor is centrifuged to remove oil, generating an effluent named "stickwater". Stickwater accounts for approximately 60% of processed fish weight, and protein is one of its major components (5–9%) [3,4]
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