Stability of levan produced by Zymomonas mobilis

The stability of levan produced by Zymomonas mobilis 113 “S” was investigated during storage of culture liquid at different pH and temperatures. Levan was not degraded if stored in a culture liquid for 120 h at 30 or 25 °C, but at 55 or 60 °C the degree of degradation was inversely proportional to pH. Cell biomass and levan sediment components did not cause the degradation of levan. The influence of organic acids (lactic-, acetic-, and gluconic) and HCl as levan hydrolyzing agents at pH 3.7, temperature 30 °C or 55 °C was investigated in a model solution. The hydrolytic effect was similar in the case of organic acids-ensuring more fructose formation, while HCl ensured higher amounts of fructo-oligosaccharides (FOS) and/or low molecular weight levan. Consequently, acid hydrolysis acts as a main levan degrading factor during storage in a culture liquid.