KINETICS OF STARCH HYDROLYSIS WITH BACILLUS AMYLOLIQUEFACIENS-ALPHA-AMYLASE UNDER HIGH HYDROSTATIC-PRESSURE

Kinetic studies on the isothermal pressure inactivation of Bacillus am yloliquefaciens alpha-amylase (BAA) in Tris/HCl buffer and in 15.% (w/ v) starch solution were performed at 25 degrees C. The reaction rate o f hydrolysis was studied at 25 degrees C under high pressure condition s. The inactivation kinetics and the pressure dependence of the hydrol ysis reaction could be described with a first-order kinetic model. The activation volume of the enzyme inactivation reaction in 0.05M Tris/H Cl buffer pH 7.2 was calculated as -28.4+/-12.2cm(3)/mole and in 1.5% (w/v) starch solution pH 7.2 the activation volume was -13.8+/-2.1cm(3 )/mole. The difference of the activation volumes obtained confirm the protective effect of the substrate against pressure inactivation. The hydrolysis of starch was found to be retarded with increasing pressure and the resulting activation volume of the hydrolysis was +22.7+/-1.9 cm(3)/mole. In preliminary studies the inactivation kinetics in buffer solution was found to strongly depend on the initial enzyme concentra tion. A high pressure pretreatment of the substrate resulted in no cha nges in the digestibility of the substrate.