Lactase Immobilized on Alumina

Abstract

A commercial neutral lactase (kluyveromyces lactis was immobilized on inexpensive alumina activated with tolylene-2,4-diisocyanate. Heat treatment of the alumina at 500 C for 48 h was effective in promoting the tolylene-2,4-diisocyanate reaction with its surface. Lactase immobilized on the tolylene-2, 4-diisocyanate-activated alumina exhibited good activity with minimal enzyme leakage. The treatment of alumina with tolylene-2,4-diisocyanate resulted in an approximate 16-fold increase in catalyst activity compared to simple adsorption on untreated alumina. Maximum lactase activity was bound at pH 7.5 in the immobilization procedure. The “optimum” temperature of the enzyme decreased from 45 C to 40 C upon immobilization. Maximum enzymic activities of both soluble and immobilized lactase were at pH 6.5, but the immobilized lactase exhibited a slightly broader pH profile. The immobilized lactase possessed slightly better storage stability over the soluble enzyme after 68 days at 4 C. Preliminary investigations on long-term hydrolysis of an ultrafiltrate of Cheddar cheese whey in a fluidized bed reactor indicated a 46% decrease in catalyst activity over the first 22 h of reactor operation. Subsequent inactivation over the next 26 h was minimal. © 1980, American Dairy Science Association. All rights reserved.