Optimization of fermentation parameters

Aspergillus awamori var. kawachi, which was found to produce high amount of

raw starch-digestive amylase (Shinsaku et al., 1982), more than 16% g/v ethanol

during sake fermentation by sake yeasts (Hiroshi et al., 2005) and highest final

ethanol concentration of 17.04% g/v was obtained in 5 days using S. cerevisiae

1200 strain in the presence of fungal mycelium, A. niger 817, and intermittent

addition of 64 g of sucrose. While in the absence of fungus it produced only

14.24% g/v ethanol in 6 days with 55 g of sucrose added intermittently and 16.32%

and 16.8% g/v ethanol were obtained from chicory and dahlia inulin, respectively

within 3 days using the above 5 day culture as source of inulinase (Kazuyoshi et

al., 1993). These reports further support our view that R3DSC5 strain can also

be considered as a high ethanol producing strain. In addition, it accumulates

maximum ethanol within two days which is earlier than those mentioned in the

above reports and hence can further reduce the cost of ethanol production. It may

produce more ethanol in analytical/large-scale fomenters where parameters can be

more efficiently controlled compared to shake flask.

Effect of initial pH

Growth pattern was found to be similar at all initial pH values for both the strains.

However, for R3DPMP strain growth is slightly less at initial pH 3 in comparison

with other pH and ethanol production pattern is similar at initial pH 5, 7 and 9

whereas ethanol production at pH 3 is slightly less. For R3DSC5 strain, maximum

growth was reached 24 hours earlier at initial pH 5 and 7 in comparison with other

pH and eventually ethanol production pattern was also similar at initial pH 5 and 7

with slightly higher and lower ethanol levels at initial pH 5 and 3 respectively.

Effect of temperature

For R3DPMP strain, maximum growth was observed at 30°C at 24 hours whereas

increase in growth was not observed at 45°C which indicates this strain cannot

grow at this temperature (Fig. 3). Moreover, in another experiment, growth was

not observed when this strain was subjected to heat treatment at 45°C for 48 hours

and the temperature was later brought back to 30°C. Rate of glucose utilization

is almost three times less at 40°C in comparison with 30 and 35°C. For R3DSC5

strain, maximum growth was observed at 35°C at 24 hours whereas increase in

growth was not observed at 40 and 45°C (Fig. 4). Active bubbling was also not

observed at 45°C during fermentation when compared with other temperatures. It

indicates that this strain cannot grow at 45°C temperature. However, in another

experiment, growth was observed within 9 hours at 30°C after subjecting this strain

to heat treatment at 45°C for 48 hours. This indicates that this strain is superior

to R3DPMP strain with respect to temperature tolerance. Ethanol production was

found to be similar at 30 and 35°C temperatures whereas ethanol accumulation

was about 3% less at 40°C in comparison to those at 30 and 35°C temperatures.

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

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