EFFICIENT BIOTRANSFORMATION OF D-GALACTOSE TO D-TAGATOSE BY ACIDOTHERMUS CELLULOLYTICS ATCC 43068

Abstract

ABSTRACT An efficient method for biotransformation of D-galactose to D-tagatose was achieved by a whole-cell L-arabinose isomerase reaction of Acidothermus cellulolytics ATCC 43068 for the first time. It was observed that the strain grew well on the most carbon sources, whereas cells grown on cellobiose demonstrated the highest conversion capability. In addition, effect of reaction parameters such as pH, temperature and substrate concentration on the conversion of the isomerization was investigated. The optimum conversion ratio of D-galactose to D-tagatose reached 50.9% at pH 7.5, 75C when the substrate concentration was 50 mM. D-tagatose was separated to the purity of 95% by Ca2+cation exchange resin with a recovery of 83% and the identity of D-tagatose was confirmed by high-performance liquid chromatography analysis and 13C-Nuclear Magnetic Resonance spectra. Acidothermus cellulolytics ATCC 43068 will be a good candidate of L-AI origin for D-tagatose production on a mass scale. PRACTICAL APPLICATIONS D-tagatose, as one of the rare sugars, has been found to be natural and safe low-calorie sweetener in food products and is classified as a generally recognized as safe substance in the United States. It has attracted a great deal of attention in recent years as a low calorie sugar-substituting sweetener, an intermediate for synthesis of optically active compounds, and as an additive in detergent, cosmetic, and pharmaceutical formulations. L-arabinose isomerase (L-AI, EC 5.3.1.4), catalyzing the isomerization of D-galactose to and D-tagatose, is regarded as the most feasible catalyst for D-tagatose biotransformation. Isomerization at high temperature (≥60C) increases the reaction rate and allows a shift in the equilibrium toward D-tagatose, which is desirable for industrial use. In this article, a thermophile bacterium capable of producing L-arabinose isomerase was screened for the biotransformation of D-tagatose from D-galactose, which will be a good candidate of L-AI origin for industrial applications.