Fermentative production of microbial levan
Microbial production of exopolysaccharides is mostly carried out using submerged fermentation techniques (Han, 1990). Cultural conditions required for both the growth of microorganism and the production of polysaccharide is unique for each and every microbe and for the polymer too. Environmental conditions such as pH, temperature, aeration and agitation must be established and optimized for each organism for increased yields. The production of levan can also be done in vitro using the enzyme levansucrase with medium containing sucrose as energy source ( Abdel-Fattah et al., 2005). Practically the yield of observed microbial levan is less than 58% of the theoretical yield (Rhee et al., 2005).
Different production strategies employ different organisms and organism specific production conditions for better and enhanced yield. Concentration of carbon, nitrogen source and other minor nutrients play an important role in the growth of the microorganism and as well as the production of microbial levan. A comprehensive list of different production strategies is given in Table 1. The microbial production as well as recovery of levan is schemed in Fig. 3.