Characterization of dextran produced from Leuconostoc citreum S5 strain isolated from Korean fermented vegetable

The production of dextran was optimized by a novel Leuconostoc citreum, which was isolated from Korean traditional fermented vegetable, Dongchimi. This strain was identified as Leuconostoc citreum S5 by a physiological analysis, API-kit analysis, 16-rDNA sequencing and RAPD-PCR. The type and production of dextrans were greatly affected by the sucrose concentration, food ingredients and fermentation time. In particular, the addition of skim milk and potato powder greatly increased the consistency of the culture broth after fermentation for 12 h at 30 °C, resulting in the maximum values after 72 h. The culture broth with the highest consistency, was obtained from the defined medium containing 20% sucrose, 1.5% skim milk and 0.5% potato powder, and it showed typical pseudoplastic behavior with a pH of 4.07, 1.12% titratable acidity, 472.5 Pa of the elasticity modulus (G′) and 85.0 Pa of viscosity modulus (G″). In addition, total dextran is composed of soluble dextran (33.2 g/L) and insoluble dextran (29.8 g/L). The conversion yield of sucrose was decreased by an increase, in the sucrose concentration in a defined medium, remaining sucrose and some of glucose and fructose. High-molecular weight dextran (2,000 kDa), as a minor fraction, was produced by increasing the sucrose. With the addition of food ingredients such as skim milk and potato powder, however, the conversion of sucrose is complete, showing only some fructose as a by-product. Low-molecular weight dextran (1,100 kDa) was only produced regardless of sucrose concentration.