Repeated-batch production of galactooligosaccharides from lactose at high concentration by using alginate-immobilized cells of Sporobolomyces singularis YIT 10047

We investigated the production of galactooligosaccharides (GOS) from lactose by alginate-immobilized cells of Sporobolomyces singularis YIT 10047 (IM-SS). beta-Galactosidase activity was stable at 30 to 50 degrees C but decreased dramatically between 50 and 60 degrees C and disappeared at 70 degrees C in acetate buffer. The enzyme activity remaining was no more than 20% of that of unheated samples after incubation in distilled water at 55 degrees C, whereas its value was about 60% at the same temperature under buffered condition. However, activity was maintained more than 80% with 10% to 50% (w/w) lactose after incubation at 55 degrees C without buffer. In a single-batch reaction, GOS yield was 41.0% with free cells and 40.4% with IM-SS. We attempted a repeated-batch reaction using IM-SS with 600 g L-1 lactose. IM-SS produced GOS stably for 20 batches (22 h/batch, 440 h in total) at 55 degrees C and pH 5.0 or 6.0. IM-SS produced GOS at 242 g L-1, at a rate of 8.72 g L-1 h(-1). Both GOS yield and production rate were higher than those in published experiments on GOS production using immobilized biocatalysts. The repeated-batch reaction with IM-SS would be an ideal system for GOS production because of its stability and high productivity.