ABSTRACTEnzymatic hydrolysis of lactose in cottage cheese whey ultrafiltrate was investigated. Lactase of A. niger was immobilized on an alumina‐silica catalyst support by the linking agent tolylene‐2, 4‐diisocyanate. The resulting immobilized enzyme preparation had an activity of 3 standard international units of lactase per gram at pH 4 and 37 °C. The optimum pH and temperature for hydrolysis of lactose by immobilized lactase were 3.5 and 50°C, respectively. Immobilization of the enzyme resulted in reductions of 1.1 pH units and 15°C in optimum pH and temperature, respectively.The two constants of the simple Michaelis‐Menten rate expression were obtained from Lineweaver‐Burk plots of the initial reaction rate data obtained at 37°C. Estimated values for Vmaxand the apparent Kmwere 7.8 (μmoles/min‐g) and 0.26 (M), respectively.Inhibition by the product galactose was measured by studying the hydrolysis reaction in a batch reactor. The inhibition constant Kiwas estimated from batch reactor data to be 0.005 and 0.053 (M) at 35 and 50°C, respectively.Activation energies of 8.1 and 6.4 (kcal/gmole) were obtained for the immobilized and soluble enzyme reactions, respectively.The behavior of the batch reactor as measured in terms of a plot of conversion versus time was essentially the same for both conventional and deionized w
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