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

Abbreviation

EPS, Exopolysaccharide; WPC, whey protein concentrate; LAB,lactic acid bacteria; GRAS, generally regarded as safe; MRS, Man Rogosa Sharpe;°T , titratable acidity; HPLC, high-performance liquid chromatography; DEAE,diethylaminoethyl.