KINETIC MODELING OF THE ENZYMATIC HYDROLYSIS OF PROTEINS OF VISCERAS FROM RED TILAPIA (Oreochromis sp.): EFFECT OF SUBSTRATE AND ENZYME CONCENTRATION

Background: The Growth of world Aquaculturehas generated important environmental impacts as discard residues that are important sources of protein which have been used to manufacture low-value products, such as animal food, fish flour and fertilizers. Objectives: To evaluate the effect of enzyme and substrate concentration on the degree of hydrolysis (DH) of proteins in the red tilapia (Oreochromis sp.) viscera (RTV). Methods: The commercial Alcalase 2.4 L enzyme was used at different concentrations to hydrolyse the proteins in RTV at 53.5 °C and a pH of 9.5 in a 1 L magnetically stirred, jacketed, glass batch reactor connected to an automatic titrator. Each experiment was conducted over 6 h in which every consumed volume of base was recorded every 5 min to determine the corresponding DH at each point. Results: The results indicated that increasing the enzyme concentration produced an increase in the DH and in the reaction rate, while increasing the substrate concentration produced a decrease in both parameters. For this reason, a mathematical model was adjusted for the inhibition of substrate from the exponential kinetic Equation d(DH)/dt = aEXP[-b(DH)] to explain the behavior of the DH as a function of substrate concentration in this hydrolytic process. The parameters a and b were estimated from a nonlinear regression. Based on these results, the reaction constants were determined as Ks=456.75 g L-1, K2=1.2191 min-1, Kd=0.2224 min-1, KM =1.8963and K3 = 0.1173 L g-1 min-1, which allowed the generation of a strong correlation between the predicted and experimental values at the different evaluated operating conditions. This correlation was supported by a low average relative error (ARE) of 3.26%. Conclusion: Under evaluated experimental conditions, the kinetics of the hydrolysis reaction followed a substrate inhibition mechanism, which was adjusted through a typical exponential Equation that involves two parameters (a and b) associated with the kinetic constants (Ks, K2, and Kd).