Gluco-oligosaccharide and galacto-oligosaccharide production by Rhodotorula minuta IFO879

Three strains of yeast, Sterigmatomyces elviae CBS8119, Rhodotorula minuta IFO879 and Sirobasidium magnum CBS6803, which are known to produce galacto-oligosaccharide (Gal-OS) from lactose, were found to possess strong transglucosylation abilities and to produce gluco-oligosaccharide (Glc-OS) from cellobiose. Among them, R. minuta IFO 879 was selected as the best producer of Glc-OS. Efficient production conditions for Glc-OS from cellobiose and Gal-OS from lactose were investigated. Using toluene-treated resting cells of R. minuta IFO879, the maximal amounts of Glc-OS produced from 200 mg/ml cellobiose and of Gal-OS produced from 200 mg/ml lactose were 70 mg/ml (a yield by weight of 35%) and 76 mg/ml (a yield by weight of 38%), respectively. Since the by-product glucose was found to inhibit oligosaccharide production, it was removed from the reaction mixture by devising a suitable culture method such that the enzymatic reaction was accompanied by cell growth to consume the glucose. Under these conditions, the productivities were markedly improved: 201 mg/ml of Glc-OS was produced from 400 mg/ml cellobiose (a yield by weight of 51%) and 230 mg/ml of Gal-OS from 360 mg/ml of lactose (a yield by weight of 64%). The structures of the major components of Glc-OS and Gal-OS obtained by this method were identified as cellotriose and O-beta-D-galactopyranosyl-(1-->4)-O-beta-D-galacto pyrano syl-(1-->4)-D-glucopyranose (4'-galactosyl-lactose), respectively.