Alliinase (alkylsulphenate lyase, EC 4.4. 1.4), which catalyses the production of allicin, was immobilized in alginate microparticles. Addition of pyridoxal 5'-phosphate to the microparticles enhanced alliinase activity. Encapsulated alliinase were significantly higher (30 and 22%, respectively) than those of non-encapsulated alliinase at 60 degrees C and at pH 2. Therefore, microencapsulation of alliinase with alginate can offer an effective way of sustaining enzyme activity during oral administration and passage through the stomach.