Application of tris(hydroxymethyl)phosphine as a coupling agent for β-galactosidase immobilized on chitosan to produce galactooligosaccharides

beta-Galactosidase was immobilized on chitosan using tris(hydroxymethyl)phosphine (THP) as a coupling agent to produce galactooligosaccharides (GOS) from lactose. Both the THP-immobilized and the free enzymes were maximally achieved at pH 5.0 and the optimal temperature was 55 degrees C. The residual activities for the THP-immobilized enzyme and the free enzyme were 75 and 25%, respectively, after being incubated in 0.1 mol dm(-3) sodium acetate buffer (pH 5.0) at 55 degrees C for 13 days. The formation of GOS was catalyzed by free and THP-immobilized beta-galactosidase from lactose. The yield of GOS produced by the free enzyme from the lactose solution (36%, w/v) at 55 degrees C was 43% on a dry weight basis, which was similar to the 41% GOS yield produced by the THP-immobilized enzyme system. (c) 2005 Society of Chemical Industry.