Direct Production of l-Tagatose from l-Psicose by Enterobacter aerogenes 230S

l-Tagatose was produced directly from l-psicose by subjecting the same biomass suspension to microbial reduction followed by oxidation using a newly isolated bacteria Enterobacter aerogenes 230S. After various optimizations, it was observed that cells grown on xylitol have the best conversion potential. Moreover, E. aerogenes 230S converted l-psicose to l-tagatose at a faster rate in the presence of polyols such as glycerol, d-sorbitol, ribitol, l-arabitol, d-mannitol and xylitol. At 5% substrate concentration, the conversion ratio of l-psicose to l-tagatose was above 60% in the presence of glycerol. Identity of crystalline l-tagatose was confirmed by HPLC analysis, 13C-NMR spectra, and optical rotation.