Durbha et al.

glucose during fermentation otherwise, contamination problems will occur during

storage of various brewery products. Maximum quantities of ethanol i.e., 8.3% g/v

for R3DPMP and 13% g/v for R3DSC5 were noticed under these experimental

conditions. As the above result suggested that maximum amount of ethanol was

produced with inoculums of 7, 8 and 9×10 8 cells/ml, inoculum densities within this

range were selected for further detailed studies with both the strains. Kazuyoshi et

al., 1993 also observed early accumulation of ethanol with higher inoculum.

Effect of glucose concentration

For R3DPMP, maximum growth of 11.3×10 8 observed with 20% g/v glucose (Fig.

1.). Percentage yield of ethanol at 5, 10, 15, 20 and 25% glucose concentrations

are 86, 93.8, 80.8, 81.2 and 80 respectively. Though the maximum yield was

observed with 10% glucose concentration at 12 hours, 20% glucose concentration

was selected since higher growth and early ethanol production were observed.

At all glucose concentrations, residual glucose reached less than 0.33% which

indicates that glucose was used up completely by this strain.

For R3DSC5, increase in cell number was observed (Fig. 2) at all other percentages

except 5%. Maximum growth of 10×10 8 cells was observed at 10, 15 and 20%

initial glucose concentrations. Yield of ethanol at 5, 10, 15, 20, 25 and 30% of

glucose are 89.9, 97.7, 95.2, 92.3, 97.7 and 91.9 respectively. Although highest

ethanol of 14.1% g/v (17.625 v/v) was produced by 60 hours with 30% glucose

concentration, 25% initial glucose concentration was found to be the best one

because maximum growth (11.8×10 8 ) and ethanol production of 12.5% g/v (15.6%

v/v) were observed for this strain in comparison with lower glucose concentrations

and early accumulation of ethanol than in 30% glucose. At each initial glucose

concentration, almost complete utilization of glucose was observed at the end of

fermentation.

In brewery industry, 18 0 Plato (12g glucose/100ml) is desired to produce ethanol at

low cost (Blieck et al., 2007). In very high gravity (VHG) fermentation, pretreated

mash having glucose concentration in the range of 15–32% g/v is used (Oscar

and Sanchez, 2008). Therefore, R3DPMP strain giving 93.8% yield of ethanol at

10% g/v glucose can be recommended for brewery industry while R3DSC5 strain

that gave consistently a minimum of 90% yield of ethanol (Table 1) from 5-30%

g/v glucose concentration, could be used in both brewery and VHG fermentation.

Moreover, R3DSC5 accumulated 12.5% g/v and 13% g/v of ethanol from 25%

g/v and 30% g/v initial glucose concentrations respectively and these values are

very close to the maximum ethanol of 13.2% g/v reported by Oscar and Sanchez,

2008 during VHG.

So far, high ethanol of 16% g/v was obtained within 3 to 5 days from raw ground

corn with and without sucrose supplementation in the presence of a mutant,

74

Int. J. Bioinformatics and Biological Sci.: v.2 n.1&2, p. 71-83. March & June 2014