Fructan biosynthesis by intra- and extracellular Zymomonas mobilis levansucrase after simultaneous production of ethanol and levan

Abstract

The chemical composition of the Zymomonas mobilis biomass and the culture liquid after ethanol and levan synthesis were studied. The activities of intra- and extracellular levansucrase produced by the Z.mobilis strain 113 "S" under optimum conditions both for levan and fructooligosaccharide (FOS) synthesis were also determined. It was shown that levan production relates to the reduction of the carbohydrate and lipid content in the biomass by increasing the nucleic acid and protein content. The levan producing activity of cellular levansucrase after ethanol and levan synthesis was approximately 30-40% of the total activity in the second fermentation stage. It was established that the cell free culture liquid, containing ethanol, levan, gluconic acid and sucrose (15%) at 25 °C, did not show any additional levan synthesising activity. At optimum FOS synthesis conditions (45 °C and 70% sucrose), the cell-free culture liquid exhibited a high FOS synthesising activity (31% from total carbohydrates), with slightly reduced biomass activity. It was concluded that as a result of the simultaneous ethanol and levan production, the remaining biomass as well as the cell-free culture liquid could be used for FOS production.