Table 4.

Kinetic parameters for ethanol production by S. stipitis NRRL Y-7124 under SHF and SSF process after 72 h and 96 h respectively

Parameters	SHF	SSF
Initial sugars (g/L)	19.52	27.95
Ethanol produced (g/L)	3.83	10.31
Cells produced (g/L)	3.57	n.d
Ethanol yield (g/g)	0.289	0.387
Fermentation efficiency (%)	56.80	75.88
Cells yield (g/g)	0.18 g/g	n.d
Ethanol productivity (g/L/h)	0.239	0.214
Cells productivity (g/L/h)	0.0495	n.d

n.d: not detected (Cells production was not detected in SSF). Fermentation was carried up to 72 h in SHF and 96 h in SSF. In SHF, maximum ethanol production (3.83 g/L) was observed after 16 h followed by a gradual downfall in conjunction with regular hike in cell mass production. After 16 hrs of fermentation, 13.32 g/l sugar was consumed. Ethanol yield, productivity and fermentation efficiency was calculated taking 16 hrs into consideration. Maximum cell mass (3.57 g/L) was recorded after 72 h. In SSF, yeast inoculum was added after 24 h of enzymatic saccharification (Pre-hydrolysis) and maximum ethanol production was obtained after 48 h of incubation. In SSF, after 48 hrs of fermentation, 26.6 g/l sugar was consumed by the yeast. Ethanol yield, productivity and fermentation efficiency was calculated taking 48 hrs into consideration. Fermentation efficiency (%) was calculated as the percentage of the maximum theoretical ethanol yield (0.51 g ethanol/g sugar used). The values are mean of three replicates. Standard deviation was within 10%.