Kinetic modeling of the enzymatic hydrolysis of proteins of visceras from red tilapia (Oreochromis sp.): effect of substrate and enzyme concentration

Abstract

Background:  The Growth of world Aquaculture has 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 = a*EXP[-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 K s =456.75 g L -1 , K 2 =1.2191 min -1 , K d =0.2224 min -1 , K M =1.8963and K 3 = 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, K 2 , and K d ).