초록
Inositol is known to initiate positive effects on yeast fermentation performance, cell growth and tolerance against environmental stresses, especially high ethanol concentration. The precise mechanisms by which inositol improves such parameters are yet to be elucidated. The present study was performed to investigate the effect of inositol supplementation on growth, fermentation performance and plasma membrane fluidity during normal gravity fermentation. Yeast cells were grown in a chemically defined fermentation medium with 15% (w/v) glucose, lacking inositol and with 0.1 or 0.4g/L inositol supplementation. Cell density, cell viability, glucose consumption and ethanol production were monitored for 96hours. Plasma membrane fluidity was monitored at 24hours fermentation, representing the respiro-fermentative growth phase, by measuring generalized polarization (GP) of laurdan. The effect of ethanol on membrane fluidity also monitored by measuring GP after exposing cell to 18% (v/v) ethanol. The results of the present experiment indicated that although inositol supplementation did not seem to improve fermentation performance as assessed by glucose consumption and ethanol production, it did improve cell growth leading to higher cell densities. While inositol-supplemented cells had higher growth rates and cell density, they had significantly lower viability, thus the viable cell counts were similar with and without supplementation. There is also evidence that inositol supplementation leads to increased membrane fluidity with significantly lower GP values for yeast cells grown in the inositol supplemented media. However when exposed to high ethanol concentrations, inositol-supplemented yeasts showed a greater GP decrease than those grown without inositol. Thus, interestingly, the non- supplemented yeasts with lower baseline membrane fluidity seemed to better withstand the fluidizing effects of ethanol. We are in the process of confirming the viability of ethanol-treated cells as well as furthering the investigations on inositol effects on stress tolerance and other physiological parameters.