Enhancement of ethanol production by promoting surface contact between starch granules and arming yeast in direct ethanol fermentation.

The specific ethanol production rate of raw starch by arming yeast cells displaying alpha-amylase and glucoamylase increased significantly when the cells and starch granules settled together. The specific ethanol production rate also increased when the size distribution of starch granules was almost same as that of the yeast cells. These results indicate that the surface contact between starch granules and yeast cells is important for increasing the apparent specific activity of alpha-amylase, which was the rate-limiting factor of the direct fermentation.

Effect of flocculation on performance of arming yeast in direct ethanol fermentation.

In the direct ethanol fermentation of raw starch by arming yeast with alpha-amylase and glucoamylase, it is preferable to use a flocculent yeast because it can be recovered without centrifugation. Three types of arming yeast system, I (nonflocculent), II (mildly flocculent), and III (heavily flocculent), were constructed and their fermentation performances were compared. With an increase in the degree of flocculation, specific ethanol production rate for soluble starch decreased (0.

Evaluation of performance of different surface-engineered yeast strains for direct ethanol production from raw starch.

Four types of cell-surface-engineered yeast Saccharomyces cerevisiae displaying glucoamylase, namely, systems A, B, C, and D, were constructed to evaluate their performance in direct ethanol fermentation from raw corn starch. Systems A and B were glucoamylase-displaying nonflocculent yeast (YF237) types that secrete alpha-amylase into the culture medium and codisplay alpha-amylase on the cell surface, respectively. Systems C and D were flocculent yeast counterparts (YF207) for systems A and B, respectively.