In vitro bioactive properties of protein hydrolysates from giant squid (Dosidicus gigas) by Bacillus subtilis

Abstract

The aim of this work was the obtention and characterization of protein hydrolysates from squid muscle frozen stored as an alternative of fermentation substrate. Hydrolysates' antioxidant, antimicrobial and functional properties were obtained by fermentation via Bacillus subtilis ATCC 6633, using Dosidicus gigas mantle, stored for 20 months at -20° C. Culture media with different proportions of collagen: muscle (C0 = 100% muscle, C25 = 75% muscle + 25% collagen, C50 = 50% muscle + 25% collagen, C75 = 25% muscle + 75% collagen, C100 = 100% collagen) of giant squid, were subjected to fermentation, from 0 to 8 hrs. Free radical scavenging activity was determined via the ABTS•+ methodology (maximum value of 3.99±0.02 mg L-ascorbic acid equivalents for 8 h-C25) and DPPH• (maximum value of 750.29±13.57 µg L-ascorbic acid equivalents for 8 hC75). Inhibition zones (between 10 mm and 14.9 mm) were found in hydrolysates, with 8 hrs of fermentation for Gram-negative bacteria. Regarding infrared spectroscopy, after 8 hrs of fermentation, several peaks were detected, which suggest the presence of aromatic rings (1582 cm-1, 856 cm-1 and 756 cm-1), in addition to peaks that suggest the presence of surfactant from B. subtilis (1510 cm-1, 1392 cm-1 and 1198 cm-1). A maximum of 150% (v/v) in the foaming capacity of 2 h-C100 and 87.5% (v/v) of 8 h-C50 was obtained; for foam stability, 77.5% (v/v) with 2 h-C100 and 22.5% (v/v) with 0 h-C0. The maximum value for the emulsifying activity index was 1778.06±30.85 m2/g of protein for 8 h-C0, while the highest index of emulsion stability was 82.04±2.81 mins for 8 h-C25. The protease activity present in the hydrolysates decreased the hardness of the gelatin to 29.6%. Results showed that the use of the giant squid stored for extended periods in freezing conditions impedes its spoiling and harmful effects on the environment, and allows the obtention of hydrolysates with antioxidant, antimicrobial and functional properties, for which the submerged fermentation with B. subtilis ATCC 6633 is suitable for the acquisition of bioactive peptides, which can be considered for their use in the food and pharmaceutical industries.