BIOCONVERSION OF D-GALACTOSE INTO D-TAGATOSE

D-Tagatose has potential food uses as a humectant and/or non-calorific sweetener. A variety of different microbial strains were tested for ability to produce D-tagatose from D-galactose. As a result, we have found that D-tagatose can be produced from D-galactose by the lactic acid bacterium Lactobacillus gayonii. Surprisingly, this bioconversion of a D-hexose sugar is probably carried out by an L-pentose isomerase (L-arabinose-ketol-isomerase) enzyme activity of the cells. Thus this enzyme reacts with the D-hexose isomer of its normal L-pentose substrate. Commercially available D-glucose (xylose)-ketol-isomerases did not carry out this bioconversion. Options for the optimization of this bioconversion are proposed.