Abstract:
Improving ethanol production from sugar cane molasses by Saccharomyces cerevisiae SKP1 was investigated. Twelve-hour culture of S. cerevisiae SKP1 in BSM medium containing 20 g/l of total sugar from sugar cane molasses was used as starter culture. The range of ethanol production by batch culture was 53.02 g/l to 72.70 g/l. Optimization of batch culture conditions showed the optimum conditions for ethanol production in 5L fermentor are as follows : initial pH, 4.5 ; agitation speed, 100 rpm ; no aeration ; temperature, 35 ํC; initial total sugar concentration, 165 g/l. The highest ethanol concentration produced by S. cerevisiae SKP1 by batch culture was 72.70 g/l or 9.20 %(v/v) at 72 h with maximum dry cell weight (DCW) of 5.47 g/l and residual total sugar 12.11 g/l, Y[subscript p/s] was 0.465 (g.ethanol/g.sugar) and ethanol productivity was 1.01 g.l[superscript 1]h[superscript 1]. It was found that increasing initial total sugar to more than 220 g/l resulted in decreasing ethanol production. Ethanol production in repeated-batch with 2 times molasses feeding at 24 h and 48 h of cultivation in order to maintain total sugar concentration at the same level as initial concentration (165 g/l). It was exhibited that 72.98 g/l of ethanol produced in shorter cultivation time (48h) due to feeding of molasses at 24 h. In comparison with batch cultivation, feeding of molasses showed no significant increasing ethanol production i.e. 80.96 g/l or 10.25 %(v/v) of highest ethanol produced at 120 h. Improving ethanol production in fed-batch culture with molasses feeding at 24 h to keep total sugar concentration in broth as nearly as that of the beginning. The highest ethanol produced was 91.12 g/l or equivalent to 11.53 %(v/v) at 84 h with 5.64 g/l of highest DCW, Y[subscript p/s] was 0.48 (g.ethanol/g.sugar) and ethanol productivity at 1.08 g.l[superscript 1]h[superscript 1]. Fed-batch cultivation with molasses feeding was better when comparing with pure glucose feeding and molasses feeding with biotin. It was shown that ethanol produced in shorter cultivation time at 36 h with pure glucose feeding. But the maximum ethanol concentration was nearly the same at 89.42 g/l at 96 h. Biotin feeding resulted in enhancing cell growth just at the early stage (12-36 h) with maximum ethanol concentration of 89.08 g/l equivalent to 11.28 %(v/v) which almost no difference from that without biotin feeding. In conclusion, ethanol production was improved by fed batch culture with ethanol concentration dramatically increased from 52.03g/l (6.71%v/v)up to 91.12 g/l which was equivalent to 11.53%(v/v)