Optimization of ethanol production through addition of substratum and protein-lipid additives was studied. Oilseed meal extract was used as protein lipid supplement, while rice husk was used as substratum. The effect of oil seed meal extract and rice husk was observed at varying concentration of medium sugar from 8% to 20%. Of the three oil seed meal extracts used, viz. groundnut, safflower, and sunflower, safflower was found to be most efficient. The use of oilseed meal extract at 4% was found to enhance ethanol production by almost 50% and enhanced sugar tolerance from 8% to 16%. A further increase of almost 48% ethanol was observed on addition of 2 g of rice husk per 100 ml of medium. An increase in cell mass with better sugar attenuation was observed. Further optimization was sought through use of sugarcane juice as the sugar source. While 8.9% ethanol yield with 75% sugar attenuation was observed at 20% sucrose concentration, it was found to increase to 12% (v/v) with almost complete utilization of medium sugar when sugarcane juice was used. Cell weight was also observed to increase by 26%.
Glycogen is an important storage reserve in yeast. In Saccharomyces cerevisiae glycogen is present in two pools, an intracellular soluble pool and a cell wall bound, insoluble extra-cellular pool. The present method uses a 20% KOH treatment to separate the two pools, which are then estimated using amyloglucosidase. The amount of soluble glycogen was found to be 6.5 mg/g of wet weight of yeast while that of cell wall bound glycogen was found to be almost three times that of the soluble, viz., 18 mg/g of wet weight of yeast. The data is compared with two earlier commonly used methods of yeast carbohydrate fractionation, which reported glycogen in totality. Reviewing these methods in the light of finding two pools of glycogen revealed that both the methods can be demonstrated to yield soluble glycogen in the range of 6-9 mg/g of yeast and 18-21 mg/g of wet weight of yeast of cell wall bound glycogen.
Novel additives that act as substratum for attachment of the yeast cells, increased ethanol production in Saccharomyces cerevisiae. The addition of 2 g rice husk, straw, wood shavings, plastic pieces or silica gel to 100 ml medium enhanced ethanol production by 30-40 (v/v). Six distillery strains showed an average enhancement of 34 from 4.1 (v/v) in control to 5.5 (v/v) on addition of rice husk. The cell wall bound glycogen increased by 40-50 mg g (-1) dry yeast while intracellular glycogen decreased by 10-12 mg g(-1) dry yeast in cells grown in presence of substratum.
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