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 in Saccharomyces cerevisiae is present in two pools as cell wall bound and intracellular glycogen. The content of the cell wall bound glycogen was found to be almost three times higher than the intracellular glycogen. The content varied with the sugar concentration in the medium and an optimum value of 22.11 mg glycogen/g yeast was observed for the cell wall bound glycogen, while it was 7 mg/g yeast for the intracellular glycogen at a 12% medium sugar content. The two pools also varied with fermentation time reaching an optimal value at 36 h of fermentation. The cell wall bound glycogen was reduced by 85% during the first three hours after pitching, when sugar uptake was minimal and started to accumulate when almost 50% of the medium sugar was utilized. It was the cell wall bound glycogen that correlated with fermentation performance. Cells grown in 8% sugar content and rich in cell wall bound glycogen, when pitched into a 1% sugar medium showed an enhancement in ethanol content by 21%. The depletion of glycogen also affected fermentation performance.