Stabilization study of tetrameric kluyveromyces lactis β-galactosidase by immobilization on immobead: thermal, physico-chemical, textural and catalytic properties

Abstract

We investigated the immobilization of a tetrameric Kluyveromyces lactis β-galactosidase (EC: 3.2.1.23) (KL-Gal) on Immobead 150 using different support modification strategies. Immobead support was modified using an acid solution of H2SO4:HNO3 (3:1) (Immobead-Ac) or 5 % (v/v) glutaraldehyde (Immobead-Glu). Its unmodified form (Immobead) was also tested. Immobilization yields and efficiencies were evaluated by testing protein loads from 10 to 200 mg.g-1 support. The thermal, physico-chemical, textural and catalytic properties of the supports (modified and unmodified) and their derivatives (Immobead-KL-Gal, Immobead-Ac-KL-Gal and Immobead-Glu-KL-Gal) were analyzed. The highest immobilization yields and efficiencies were achieved with a protein load of 100 mg.g-1 support. Surface and pore areas of the Immobead support were greatly decreased after modification. Michaelis constant of the immobilized β-galactosidase increased in the derivatives. Maximum velocity decreased approximately 2.8 times for Immobead-KL-Gal and Immobead-Glu-KL-Gal, and approximately 1.4 times for Immobead-Ac-KL-Gal. In batch processes, the three derivatives could be reused successfully at least 15 times, maintaining high residual enzymatic activity during the lactose hydrolysis (in both cheese whey and milk). The tetrameric K. lactis β-galactosidase immobilized on Immobead supports via the tested treatments was stabilized and is an alternative tool for lactose hydrolysis in the dairy industry.