ACE-inhibitory and antioxidant potential of gelatine hydrolysates from hybrid grouper bones as affected by hydrolysis duration

Aim: The fish filleting industry often generates substantial quantities of by-products such as fish bones, heads, scales, and viscera, which are frequently discarded or repurposed for low-value applications. Hydrolysate derived from fish processing wastes have demonstrated various beneficial bioactivities such as ACE-inhibitory, antioxidant, and antidiabetic activities, underscoring their potential as high value functional ingredients or foods. The potency of hydrolysate is determined by peptide composition, which is modulated by the degree of hydrolysis. This study aims to investigate the impact of hydrolysis duration on the ACE-inhibitory and antioxidant capacities of gelatine hydrolysate from hybrid grouper bones. Methods: Gelatine extracted from hybrid grouper fish heads and bones underwent hydrolysis with 1% Alcalase for varying duration (1 h, 2 h, 4 h, 6 h, 24 h, 48 h). The molecular distribution of the hydrolysates was monitored using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) electrophoresis. ACE-inhibitory and antioxidant capacities (hydroxyl radical scavenging, reducing power, metal chelating activities) of the resultant hydrolysates from different hydrolysis durations were evaluated. Results: SDS-PAGE analysis revealed that Alcalase hydrolysis of bones gelatine yielded peptides of lower molecular weight. A moderate negative correlation (r = –0.703) (p < 0.01) was reported between the degree of hydrolysis and ACE-inhibitory activity, suggesting that excessive hydrolysis diminishes ACE-inhibitory capacity. Conversely, antioxidant activity of the gelatine hydrolysates was unaffected by hydrolysis extent, as indicated by weak correlations. Conclusions: These findings indicate that optimising hydrolysis duration maximises the bioactivities of gelatine hydrolysate from hybrid grouper bones.