Immobilized lactose of A. oryzae was used for the hydrolysis of lactose in partially deproteinized whey in a fluidized-bed reactor packed with motionless mixers. The lactase was immobilized on chitosan-coated silica gel particles by means of glutaraldehyde. Both sol. and immobilized lactose followed Michaelis-Menten kinetics with product inhibition by galactose. [on SciFinder (R)]