The β-galactosidase immobilization protocol determines its performance as catalysts in the kinetically controlled synthesis of lactulose

In this paper, 3 different biocatalysts of beta-galactosidase from Kluyveromyces lactis have been prepared by immobilization in chitosan activated with glutaraldehyde (Chi_Glu_Gal), glyoxyl agarose (Aga_Gly_Gal) and agarose coated with polyethylenimine (Aga_PEI_Gal). These biocatalysts have been used to catalyze the synthesis of lactulose from lactose and fructose. Aga-PEI-Gal only produces lactulose at 50 degrees C, and not at 25 or 37 degrees C, Aga_Gly_Gal was unable to produce lactulose at any of the assayed temperatures while Chi_Glu_Gal produced lactulose at all assayed temperatures, although a lower yield was obtained at 25 or 37 degrees C. The pre-incubation of this biocatalyst at 50 degrees C permitted to obtain similar yields at 25 or 37 degrees C than at 50 degrees C. The use of milk whey instead of pure lactose and fructose produced an improvement in the yields using Aga_PEI_Gal and a decrease using Chi_Glu_Gal. The operational stability also depends on the reaction medium and of biocatalyst. This study reveals how enzyme immobilization may greatly alter the performance of beta-galactosidase in a kinetically controlled manner, and how medium composition influences this performance due to the kinetic properties of beta-galactosidase. (C) 2021 Elsevier B.V. All rights reserved.