Optimization, Characterization and Antioxidant Activity of Fish Protein Hydrolysate from Payangka (Ophieleotris aporos) using Papain and Bromelain

&lt;b&gt;Background and Objective:&lt;/b&gt; Payangka fish (&lt;i&gt;Ophieleotris aporos&lt;/i&gt;), an underutilized endemic species from Lake Tondano, North Sulawesi, Indonesia, represents a potential resource for sustainable food fortification. Despite comprising 35% of the local catch, its biochemical valorization remains unexplored. This study aimed to optimize the enzymatic hydrolysis of Payangka fish muscle protein using papain and bromelain to produce bioactive hydrolysates suitable for functional food applications. &lt;b&gt;Materials and Methods:&lt;/b&gt; Fish protein hydrolysis was performed at 55°C with a solid-to-liquid ratio of 1:4, using varying concentrations of papain and bromelain. The resulting hydrolysates were characterized for degree of hydrolysis (DH), proximate composition, color, amino acid profile and antioxidant activity. Statistical analysis was conducted to assess the effect of enzyme type and concentration on hydrolysis and bioactivity. Differences were considered statistically significant at p<0.05. &lt;b&gt;Results:&lt;/b&gt; Increasing enzyme concentration positively correlated with DH. Papain achieved optimal DH (86.5±0.01% to 93.13±0.01%) within 2 hrs, whereas bromelain reached 71.94±0.01% to 84.01±0.01% after 8 hrs. Papain-derived hydrolysates (2 hrs, 4% enzyme) showed increased protein content (0.52-0.68%) and the highest antioxidant activity (85.76%). Total essential and non-essential amino acids were 74.47 ppm and 86.30 ppm, respectively, with lysine (26.65 ppm), leucine (15.02 ppm) and valine (11.01 ppm) being dominant essential amino acids and glutamic acid (26.34 ppm), aspartic acid (17.53 ppm) and alanine (9.83 ppm) as dominant non-essential amino acids. &lt;b&gt;Conclusion:&lt;/b&gt; Fish protein hydrolysate from Payangka, particularly using 4% papain, demonstrates high bioactivity and favorable amino acid composition, highlighting its potential as a functional ingredient for food fortification. Future research could explore its incorporation into food products and long-term bioactivity.