MODELING OF PROTEIN HYDROLYSIS KINETIC USING AN ALKALINE PROTEASE FROM BACILLUS LICHENIFORMIS

M. FUENTES; C. THOMPSON; M. MUSSATI; P.A. AGUIRRE; N. SCENNA

RIo de Janeiro

Congreso; 2nd Mercosur Congress on Chemical Engineering. 4th Mercosur Congress on Process Systems Engineering; 2005

UFRJ

Many industrial and agricultural wastewaters contain appreciable amounts of proteins. Under anaerobic conditions proteins are first hydrolyzed and degraded by proteolytic enzymes into peptides and individual amino acids. The peptides and amino acids are then acidified into volatile fatty acids (VFA), hydrogen, ammonium, and reduced sulfur. The VFA are further converted by acetogens into acetate and H2/CO2, both of which are lastly converted to methane by methanogens. The aim of this work is to investigate  the kinetics of protein hydrolysis for its further application in modeling of anaerobic degradation of complex substrates. A bacterial alkaline serine protease (EC 3.4.21.14, Sigma) from Bacillus Licheniformis, an anaerobic microorganism, is used. Gelatin, which is usually found in meat wastes; albumin, in whey effluents; and soy proteins, were chosen as characteristic molecules to represent the proteins commonly found in waste effluents. A glass stirred tank (batch) reactor (1.5L) was used as experimental device. The Michaelis-Menten type model and a model considering a zero-order hydrolysis with respect to the substrate and a second-order enzymatic denaturalization are investigated to approximate the experimental data obtained by the pH-stat method. By combining the pH-stat and pH drop methods, a hydrolysis conversion of 24% and 15% higher than the experimental values was predicted for gelatin and soy, respectively. The influence of the temperature on the kinetic parameters in the range of 25°C to 50°C was assessed at pH 8. The non-competitive inhibition  by VFA was measured during hydrolysis of gelatin. An increase in the acetic acid concentration increases the inhibitory effects.