ASSESSMENT OF EXOPOLYSACCHARIDES PRODUCING LACTIC ACID BACTERIA ISOLATED FROM NUNU – A LOCALLY FERMENTED MILK IN NIGERIA

Abstract

Exopolysaccharides (EPS) are extracellular polymers made of monomers of carbohydrates, which are important in many biological mechanisms. Several lactic acid bacteria (LAB) can confer desirable properties to specific fermented products when EPSs are produced during dairy fermentation. The present study isolated LAB from a locally fermented milk (Nunu) and screened for EPS production. The LAB strain with the highest EPS production potential was selected for EPS bulk production in a modified EPS Selection Medium (mESM). The effects of pH, temperature, incubation time, and carbon source were performed for optimization studies. The obtained EPS were then analysed for their chemical characteristics like total carbohydrate content (TCHO) and monomer composition. In total, three strains of LAB belonging to the genus Lactobacillus were isolated from the fermented milk (Nunu) sample. The Lactobacillus sp. (Nu3) was the best EPS producer among others. Optimization studies revealed starch as the most appropriate carbon source, with an EPS yield of 4.86 g/100mL. Two days (48 h) of incubation time was confirmed to be optimum for producing a maximum yield of 1.02 g/100 mL. The optimum pH and temperature for EPS production were 7.0 and 30^oC, yielding 1.87 g/100 mL and 1.15 g/100 mL, respectively. A maximum EPS yield of 5.31 g/100 mL was recovered under the optimal conditions. The monomer analysis of the EPS under study revealed glucose and galactose are the main monosaccharide components, with fructose and mannose being the minor. Moreover, the EPS-producing Lactobacillus sp. (Nu3) was found to be an inventive EPS producer, and its EPS material could be utilized as an additive in the food industry.