Galacto-oligosaccharide production using a recycling cell culture of Sterigmatomyces elviae CBS8119

Addition of small amounts of Fe²⁺, Zn²⁺, Cu²⁺ and thiamine-HCl to the culture medium was required for promoting the galacto-oligosaccharide (Gal-OS)-producing activity of Sterigmatomyces elviae CBS8119, when the concentration of yeast extract in the medium was lowered to 0·1 g l^?1. Galacto-oligosaccharide production using a recycling cell culture was performed in a medium containing 360 mg ml^?1 of lactose supplemented with optimal concentrations of Fe²⁺ (1·5 mg l^?1 of FeSO₄.7H₂O), Zn²⁺ (15 mg l^?1 of ZnSO₄.7H₂O), Cu²⁺ (0·5 mg l^?1 of CuSO₄.5H₂O) and thiamine-HCl (1 mg l^?1 ) . Galacto-oligosaccharide production was maintained at high levels during six cycles of production, with the amount of Gal-OS produced in each cycle being more than 216 mg ml^?1 (weight yield of more than 60%).