Antioxidant Activity of Protein Hydrolysate from Fermented Kuniran Fish (Upeneus sulphureus) with the Addition of Pineapple Extract

Abstract

Kuniran fish (Upeneus sulphureus) is a low-economic-value species often found as bycatch but rich in protein, making it a potential raw material for protein hydrolysates. Spontaneous fermentation of fish protein can be accelerated by adding protease-rich sources such as pineapple juice, whose bromelain enzymes hydrolyze peptide bonds into simpler compounds. Protein hydrolysates from fermentation may contain bioactive peptides with antioxidant activity. This study aimed to determine the optimal pineapple juice concentration to enhance the antioxidant potential of kuniran fish protein hydrolysates. The experiment was conducted from April to July 2025 using a factorial Completely Randomized Design with two factors: pineapple juice concentration (0%, 10%, 15%) and fermentation time (0, 24, 48, 72 hours). Parameters observed included yield, protein content, pH, antioxidant activity (DPPH), and degree of hydrolysis. Results showed that 15% pineapple juice for 24 hours produced the highest yield (77.31%), while the lowest pH (4.32) was observed at 15% pineapple juice for 72 hours. Protein content decreased after 24 hours due to bromelain activity but remained relatively high (45.88%–48.85%). The best antioxidant activity (IC50 5.59 mg/mL) was obtained from 10% pineapple juice at 48 hours. The degree of hydrolysis ranged from 48.32% to 50.89%. These findings indicate that fermentation with pineapple juice effectively produces protein hydrolysates with antioxidant potential, and 10% pineapple juice at 48 hours is recommended as the optimal condition.