Enhancement of Antioxidant Capacities of Salmon Viscera Waste as an Animal Feed Additive: Effects of Continuous Process With Acid/Alkali Swelling, Enzymatic Hydrolysis, and Glycation

Salmon viscera, a protein-rich by-product of salmon processing, offers significant potential as a valuable ingredient in companion animal feed. This study aimed to enhance the antioxidant capacities of salmon viscera hydrolysates through a systematic process involving acid/alkali swelling, enzymatic hydrolysis, and glycation. The viscera were washed and swollen with distilled water (pH 5.75), acid (pH 3.18), or alkali solution (pH 8.17), followed by hydrolysis using Alcalase at 55 °C for 1 h. Glycation was subsequently performed with 1 % (w/v) D-glucose, 1 % D-xylose, or a combination of 0.5 % D-glucose and 0.5 % D-xylose at 95 °C for 1 h. The acid swelling (39.16 %) and alkali swelling (39.27 %) resulted in a significantly higher degree of hydrolysis than the control (38.16 %) and increased the release of free amino acids from 419.7 mg.100 mL-1 (control) to 512.8 mg.100 mL-1 (acid treatment) and 533.3 mg.100 mL-1 (alkali treatment), respectively (P < 0.05). Notably, alkali swelling combined with glycation, particularly with xylose, significantly enhanced the antioxidant activities of the hydrolysates. However, certain combinations of swelling and glycation resulted in diminished antioxidant activity, potentially due to the variability in glycation progress. These findings suggest that optimised combinations of acid/alkali swelling and glycation, particularly using alkali swelling and xylose, can effectively enhance the antioxidant properties of salmon viscera hydrolysates, making them promising additives for companion animal feed.