Studies on the enzymatic hydrolysis of dogfish (Squalus acanthias) muscle protein

Response surface methodology (RSM) was used to study the combined effects of pH, temperature and enzyme - substrate ratio (E/S) on the degree of hydrolysis (DH) of dogfish muscle protein. The effects of the factor variables which affect hydrolysis were described using a three-level Box-Behnken factorial design giving a mathematical model equation that showed the influence of each variable and their interactions. The optimization of the enzymatic process was performed with the RSM statistical technique having the recovery of soluble nitrogen (NR) from the original substrate as the process response. The optimum values for enzyme / substrate ratio, temperature and pH were found to be 3.7 % (w/w), 55.3 °C, and 8.3, respectively, resulting in a maximum NR of 77.68 %. The coefficient of determination (R²ad) was greater than 95 % at the 0.1 % probability level, and a lack-of-fit test revealed a non-significant value for the NR model equation, indicating that the regression equation was adequate for predicting the nitrogen recovery under any combination of values of the variables. The shark protein hydrolysate produced under these conditions contained a high crude protein concentration (> 85 %, dry weight basis), and its high nutritional value was indicated by the presence of all essential amino acids, and by high protein efficiency ratio (PER) values. The functional, physical and rheological properties of the optimized spray dried protein hydrolysate was compared to the protein hydrolysate obtained by autolytic degradation, and a control, freeze dried muscle. The Alcalase®-assisted hydrolysis, in general, improved functional properties such as solubility and dispersibility, indicating that enzymatic hydrolysis under the experimental conditions described in this study can produce a new source protein ingredient with superior protein functionality. Physical and rheological product characteristics were also subjected to significant changes. The off-white protein hydrolysate had a low viscosity in aqueous dispersions even at high protein concentration