Physicochemical Characterization of Protein Hydrolysates Produced by Autolysis of Jumbo Squid (Dosidicus gigas) Byproducts

The physicochemical characteristics of protein hydrolysates of jumbo squid (Dosidicus gigas) byproducts (JSBP) produced by endogenous proteases at two different pH values (5.0 and 7.0) were studied using destructive and nondestructive methods. Reaction mixture samples were collected at different interval times during hydrolysis to monitor changes in the level of hydrolysis (DH) using the OPA method, the protein peptide molecular masses (MM), and SDS-PAGE. The DH increased from 3.5 to 11.2 % at pH 5.0 and from 4.8 to 17.5 % at pH 7.0. Both pH treatments exhibited similar degradation patterns with progressive proteolysis and, after 120 min of hydrolysis, yielded hydrolysates that contained MM <45 kDa proteins. It was detected lower hydrophobic amino acid exposure for the protein hydrolysates prepared at pH 5.0 compared with the hydrolysates at pH 7.0. In several wavebands, higher wavenumbers were observed in the FT-IR spectra for the pH 5.0 hydrolysates. Nine different equivalent protons were observed in the NMR spectra for both hydrolysates; these protons might belong to amino acid side chains. SEM showed substantially lower particle size for the JSBPs after hydrolysis at pH 7.0. The hydrolysate zeta potentials were −29.4 mV at pH 7.0 and −10.5 mV at pH 5.0. The pH 5.0 hydrolysates exhibited lower endothermic resistance and hydrophobicity (SoANS) compared with the pH 7.0 hydrolysates. This biophysical characterization enhances the understanding of jumbo squid byproduct hydrolysate physiochemical properties, which will aid in determining the proper use of these hydrolysates.