Increased Production of Food-Grade D-Tagatose from D-Galactose by Permeabilized and Immobilized Cells of Corynebacterium glutamicum, a GRAS Host, Expressing D-Galactose Isomerase from Geobacillus thermodenitrificans

摘要

The generally recognized as safe microorganism Corynebacterium glutamicum expressing Geobacillus thermodenitrificans D-galactose isomerase (D-GaI) was an efficient host for the production of D-tagatose, a functional sweetener. The D-tagatose production at 500 g/L D-galactose by the host was 1.4-fold higher than that by Escherichia coli expressing D-Gal. The D-tagatose-producing activity of permeabilized C. glutamicum (PCG) cells treated with 1% (w/v) Triton X-100 was 2.1-fold higher than that of untreated cells. Permeabilized and immobilized C. glutamicum (PICG) cells in 3% (w/v) alginate showed a 3.1-fold longer half-life at 50 degrees C and 3.1-fold higher total D-tagatose concentration in repeated batch reactions than PCG cells. PICG cells, which produced 165 g/L D-tagatose after 3 h, with a conversion of 55% (w/w) and a productivity of 55 g/L/h, showed significantly higher D-tagatose productivity than that reported for other cells. Thus, D-tagatose production by PICG cells may be an economical process to produce food-grade D-tagatose.