Growth and exopolysaccharide production by <i>Lactobacillus fermentum</i> F6 in skim milk

Abstract

Growth and exopolysaccharide (EPS) production by Lactobacillus fermentum F6 isolated from traditional dairy products in Inner Mongolia of China were studied when the strain was grown in 10% (w/v) reconstituted skim milk under different culture conditions. The results showed that culturing of L. fermentum F6 at a temperature (37°C) and pH (6.5) optimal for growth was also favorable for EPS production. Supplementation in 10% (w/v) skim milk with different carbon sources (glucose, lactose, galactose and fructose) increased EPS production; glucose being more effective than other sugars. Supplementation with whey protein concentrate (WPC) at 0.5% (w/v) resulted in about two-fold increase in EPS production. A maximum of 44.49 mg/l of EPS was produced by L. fermentum F6 in the skim milk medium supplemented with 2% (w/v) glucose and 0.5% (w/v) WPC at 37°C and at initial pH 6.5. Monosaccharide analysis showed that the EPS of L. fermentum F6 was composed of glucose and galactose in a molar ratio of 4:3. The molecular mass of the EPS was determined to be 3.54 × 106 Da. A 1% (w/v) aqueous solution of the EPS showed relatively high viscosity, indicating the potential of this EPS to be used as a viscosifying agent in food products.

Key words: Lactic acid bacteria, Lactobacillus fermentum, exopolysaccharides.