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We have studied the enzymatic hydrolysis of whey proteins at pH 8 and50 degrees C with two proteases of bacterial origin, MKC Protease 660 L, and one of animal origin, PEM 2500 S. Our results show that a greater degree of hydrolysis is achieved under the same experimental conditions with the bacterial proteases than with the animal one. In our interpretation of the results we propose a mechanism in which the hydrolytic reaction is a zero-order one for the substrate, and the enzyme denaturalizes simultaneously via a second-order kinetic process due to free enzyme attacking enzyme bound to the substrate. Our results also indicate that there is an irreversible serine-protease inhibitor in whey proteins. (c) 1994 John Wiley & Sons, Inc.

The effects of temperature (25–40°C), H2SO4 concentration (31–70% (w/v)) and the acid/substrate relationship (1–5 cm3 of H2SO4 per g−1 of cellulose) on the solubilization rate of microcrystalline cellulose and on the glucose production rate have been analysed. The solubilization process was by determining reducing groups present in solution. For acid/substrate relationships of more than 1 cm3 g−1 and H2SO4 concentrations of greater than 62% (w/v), the acid promoted the total solubilization of the cellulose in the form of chains with a low degree of polymerization within 4 h. The solubilization demonstrated zero‐order kinetics in which the specific rate and time of total solubilization are a function of the variables in operation. Glucose was produced according to a mechanism of two consecutive first‐order pseudo‐homogeneous reactions. The values of the kinetic constants k1 and k2 have been correlated with temperature, the H2SO4 concentration and the acid/substrate relationship.

We study the enzymatic hydrolysis of lactose by a commercial enzyme from a selected strain of Kluyveromyces fragilis. The variables analyzed were: temperature (25-40 • C), enzyme concentration (0.1-3.0 g l −1 ), lactose concentration (0.0278-0.208 M), and initial galactose concentration (0.0347 M). On the basis of the data analyzed, both published and in the present work, we propose a Michaelis-Menten kinetic model with inhibition by the product (galactose), which reveals that the substrate (lactose) and the product (galactose) present similar affinity for the active site of the enzyme.