Improvement of lactuluse synthesis through optimization of reaction conditions with immobilized beta-galactosidase

Abstract

Kluyveromyces lactis beta-galactosidase was immobilized on silica gels using a covalent bonding method. To improve lactulose synthesis using immobilized beta-galactosidase, the optimal reaction conditions, such as lactose and fructose concentrations, pH and ionic strength of the buffer, loading amount of the enzyme and temperature, were determined. Lactulose synthesis using the immobilized beta-galactosidase was markedly improved after optimization of the reaction conditions. When the lactulose synthesis was carried out at 47 degrees C using 40% (w/v) lactose, 20% (w/v) fructose and immobilized beta-galactosidase of 12 U/ml in 50 mM sodium phosphate buffer at pH 7.5, the lactulose concentration and specific productivity were 15.80 g/l and 1.32 mg/U.h, respectively. In addition, when the immobilized beta-galactosidase was reused for lactulose synthesis, its catalytic activity retained 60.5% after 10 reuses.