Tholath Emilia Abraham, Kumud Kumari
Flocculation is a useful property of industrial yeast (Saccharomyces) strains in fermentation, brewing, wine making and ethanol and biomass production. Preparation of biocatalyst particles containing yeast, for continuous production of ethanol, has a lot of economic feasibility due to increased microbial hold up, ease of separation of biomass from the fermentation media, possibilities for use in novel fermentation configuration. Recent advances in the design of continuous fermentation systems to shorten the fermentation time call for the use of flocculent strains for maintenance of cell population density. The degree of flocculation is a critical parameter since it severely affects the fermentation rate, time and production cost. It is essential that if high alcohol-yielding strains have to be used for fermentation, artificial flocculation methods have to be adopted. Flocculation by cationic polyelectrolyte (0.1-0.5 mg/mi) in the presence of Calcium ions (0.004-1.0 M/ml) was found to flocculate most of the yeast strains. Operation of a Tower fermentor for the production of ethanol with the flocculated /clustered yeast gave a productivity of 2- 4.5 gm/L/h which was higher than the batch production with the same flocculated yeast. This yeast can be used for various biotransformations as well as desugaring any solutions of importance. The use of artificially flocculated yeast will make the process cost effective. Compared to the gel entraped yeast particles , artificially flocculated cells have high cell density and have efficient conversions.