Levan production with a flocculent strain of<i>zymomonas mobilis</i>

Abstract

Abstract Levan is a fructose polymer with potential importance as fructose source or thickening agent in food technology in case that it could be produced in a simple and cheap process. Levan concentrations of up to 42.5 g/L and a yield from fructose of 032 g/g were obtained with a new flocculent mutant of Zymomonas mobilis. A sucrose concentration of 250 g/L, pH‐values around 5.0 and temperatures of 27 to 30 °C were optimal. Higher pH‐values and high starting concentrations of levan caused hydrolysis of the polymer by the bacterium itself. However, adding levan up to 1.5 g/L led to nearly 40 % increase of the levan synthesis. Sorbitol also increased levan formation due to a decrease of sucrose and levan hydrolysis. Presumably by induction of the levansucrase, fructose addition caused a higher levan yield too. In continuous operation, a levan productivity of 16 g/L.h and an ethanol productivity of 26.3 g/L.h resulted. That was 5 to 12 times, respectively the productivity of batch processes. These results are interpreted as very promising.