Exopolysaccharides are high molecular weight polymers composed of sugar subunits. Produced exopolysaccharides by lactic acid bacteria (LAB) play a significant role in improvement of organoleptic properties of fermented dairy products such as yogurt. Diversely, the probiotic function of these bacteria and the prebiotic properties of their produced biopolymers promote consumer’s health. For this purpose, a traditional dairy product known as “Kishk” was selected. 143 strains of lactic acid bacteria were isolated from Iranian Kishk in Khorasan Province and cultured in formulated MRS mediums with different sugars such as glucose, fructose, sucrose and, lactose (40 g/L) and incubated in anaerobic conditions at 30 and 37°C for 48 hours. The microscopic features of the isolates were assessed and the production of exopolysaccharide in the culture medium was evaluated by disk and ruthenium red methods. The phenol-sulfuric and weight method were used to quantify exopolysaccharide production. Results showed pH of Kishk samples ranged from 3.60 to 4.08 and the average of total mesophilic count and LAB count of samples were 6.50 and 5.89 log CFU/g, respectively. Analysis of data exhibited 79 out of 143 lactic acid bacteria isolates were exopolysaccharide producer and 70% of them were cocci. The average of maximum and minimum production by weight method were 2.61 g/L and 0.08 g/L, respectively. The average of highest and the lowest amount of exopolysaccharide by phenol sulfuric method were measured 1.87 g/L and 0.06 g/L, respectively. This study indicates the potential of exopolysaccharide production by Iranian native species from dairy products.

Keywords