Low molecular weight dextran production by Leuconostoc mesenteroides strains: Optimization of a new culture medium and the rheological assessments

Abstract

Strains belonging to genus Leuoconostoc mesenteroides are able to produce dextran exo-polysaccharide. In this study, MRS broth and milk permeate were used for growth of three strains (NRRL B-512F, NCIB 8023 and NRRL B-512) of L. mesenteroides and the growth rate, dextran production, and its rheological properties were studied. Evaluation of molecular weight by high-performance size exclusion chromatography system showed that dextran produced in milk permeate had a lower molecular weight (<10000 Dalton) compared to the dextran produced in MRS broth (<40000 Dalton). The viscosity of dextran solution (2%) produced in MRS was 0.005–0.01 Pa.s while in the synthetic medium it was <0.005 Pa.s. Also in our study maximum ratio of growth factor and dextran yield belonged to NRRL B-512F, which was subjected to optimization of fermentation condition for dextran production. For optimization, response surface methodology by using sucrose, milk permeate and yeast extract in 5 levels were used. According to experiments, optimum concentrations for sucrose, milk permeate, and yeast extract were found to be 20, 15, and 15 (g/l), respectively.