Application of NAD-dependent polyol dehydrogenases for enzymatic mannitol/sorbitol production with coenzyme regeneration.

D-Mannitol and D-sorbitol were produced enzymatically from D-fructose using NAD-dependent polyol dehydrogenases. For the production of D-mannitol the Leuconostoc mesenteroides mannitol dehydrogenase could be used. Gluconobacter oxydans cell extract contained however both mannitol and sorbitol dehydrogenase. When this cell extract was used, the reduction of D-fructose resulted in a mixture of D-sorbitol and D-mannitol. To determine the optimal bioconversion conditions the polyol dehydrogenases were characterized towards pH- and temperature-optimum and -stability. As a compromise between enzyme activity and stability, the bioconversion reactions were performed at pH 6.5 and 25 degrees C. Since the polyol dehydrogenases are NADH-dependent, an efficient coenzyme regeneration was needed. Regeneration of NADH was accomplished by formate dehydrogenase-mediated oxidation of formate into CO2.

A new xylanase from Penicillium griseofulvum.

A new xylanase (pgxynA) from Penicillium griseofulvum A160 has been isolated and characterised using a screening method based on the ability to digest a complex substrate. The enzyme belongs to the hydrolase family 11 or G and shows an optimum pH of 5.0 and an optimum temperature of 50 degrees C. The xylanase breaks down the xylan to very small oligosaccharides. The corresponding gene (PGXYNA) was cloned and expressed in Aspergillus oryzae. A second xylanase gene with 66% identity to PGXYNA has also been isolated from P. griseofulvum A160. The recombinant pgxynA xylanase has been tested in some industrial applications. In bread making, hard rolls volume increased significantly using this enzyme. In wheat flour processing, the enzyme improved the separation of gluten from starch. In poultry, the addition of the A160 xylanase to a wheat-based diet led to an higher body weight as well as to a better feed conversion ratio.