Variation in the molecular mass of exopolysaccharides during the time course of extended fermentations of skimmed milk by lactic acid bacteria

The weight average molecular mass (M-w) of the exopolysaccharide (EPS) secreted by Lactobacillus acidophilus 5e2 when grown on skimmed milk supplemented by glucose was monitored during extended fermentation times. During the exponential growth phase, the increase in M-w closely followed the increase in yield of EPS. Under the fermentation conditions applied in this study, few if any new polysaccharide chains were formed during this growth phase despite a twenty five-fold increase in the cell count: almost the entire increase in yield can be accounted for by an increase in chain length. These results suggest that synthesis of new EPS chains is switched off during the exponential and stationary phase of fermentation. The increase in yield observed in this period is a consequence of the bacteria's ability to extend existing chains right up to the mid-stationary phase. These results raise questions about the factors that control EPS production and chain length. (C) 2009 Elsevier Ltd. All rights reserved.