USE OF IMMOBILIZED LACTASE IN PROCESSING CHEESE WHEY ULTRAFILTRATE

Enzymatic 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 V_max and the apparent K_m were 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 K_i was 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 whey ultrafiltrate.