ORIGINAL PAPER Characterization of dextran produced from Leuconostoc citreum S5 strain isolated from Korean fermented vegetable Min-Jung Son Æ Eun-Kyung Jang Æ Oh-Sik Kwon Æ Ji-Hyun Seo Æ In-Jung Kim Æ In-Seon Lee Æ Seung-Chun Park Æ Sam-Pin Lee Received: 28 September 2006 / Revised: 9 January 2007 / Accepted: 22 January 2007 / Published online: 13 February 2007 Ó Springer-Verlag 2007 Abstract 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 con- centration, food ingredients and fermentation time. In particular, the addition of skim milk and potato pow- der 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 pseudo- plastic 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 com- plete, showing only some fructose as a by-product. Low-molecular weight dextran (1,100 kDa) was only produced regardless of sucrose concentration. Keywords Leuconostoc citreum  Dextran  Consistency  Skim milk  Potato powder Abbreviations LAB Lactic acid bacterium BPB Bromophenol blue RAPD Random amplified polymorphic DNA PCR Polymerase chain reaction Introduction Dextrans are defined as homopolysaccharides of glu- cose that has a(1–6) glycosidic linkage in their major chains [1]. Most microbial polysaccharides are secreted after the synthesis of inside cells, but dextrans are produced from sucrose extracellularly by secreted enzymes commonly referred to as glucansucrases or dextransucrases [2]. J.-H. Seo  I.-S. Lee  S.-P. Lee (&) Department of Food Science and Technology, Keimyung University, Daegu 704-701, South Korea e-mail: splee@kmu.ac.kr M.-J. Son  E.-K. Jang Traditional Microorganism Resources Center, Keimyung University, Daegu 704-701, South Korea O.-S. Kwon Department of Microbiology, Keimyung University, Daegu 704-701, South Korea I.-J. Kim Faculty of Biotechnology, College of Applied Life Sciences, Jeju 690-756, South Korea S.-C. Park College of Veterinary Medicine, Kyungpook National University, Daegu 702-701, South Korea 123 Eur Food Res Technol (2008) 226:697–706 DOI 10.1007/s00217-007-0579-y