Effect of the shear rate on pullulan production from beet molasses by Aureobasidium pullulans in an airlift reactor

The effect of the shear rate on pullulan production from beet molasses by A ureobasidium pullulans P56 in an airlift reactor was investigated. A maximu m polysaccharide concentration (18.5 g/L), biomass dry weight (14.0 g/L), p olysaccharide yield (38.5%), and sugar utilization (96%) was achieved at a shear rate of 42 s(-1). A. pullulans grown on beet molasses produced a mixt ure of pullulan and other polysaccharides. The highest value of pullulan pr oportion (30% of total polysaccharide) was obtained at a low shear rate (42 s(-1)). The apparent viscosity of the fermentation broth increased as the shear rate increased up to 42 s(-1) and then decreased. On the other hand, the dissolved oxygen concentration and the volumetric mass transfer coeffic ient increased with the increase of the shear rate from 21 to 84 s(-1). The external addition of L-glutamic acid, olive oil, and Tween-80 improved sig nificantly the production of crude polysaccharide (27.0 g/L), but the pullu lan content of the polysaccharide was low (20%).