Bioethanol production from sugarcane juice by yeast
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Date
2008
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Publisher
CCSHAU
Abstract
Ethanol is an important feed stock for industrial and potable purposes. However,
recently the use of ethanol as fuel purpose is catching up faster world over. It is mostly
produced by fermentation of molasses by Saccharomyces cerevisiae. Molasses has become
expensive due to decontrol and is of poor quality. Sugarcane juice can be cheaper and readily
available alternate substrate for ethanol production. Fourteen yeasts isolates from soil and
sugarcane juice samples collected from various sources (local cane crushers, sugarcane fields
and sugar mills), were picked up from YEPS medium plates following enrichment culture
technique. In the initial screening the isolates RY-1 to RY-14 along with the reference strain
showed high variability in alcohol production from sucrose and sugarcane juice. Ethanol
production was more from sugarcane juice as compared to sucrose. The two isolates (RY-5 and
RY-8) gave more ethanol (7.18 and 8.19%) from sugarcane juice compared to rest of isolates
and were finally selected for subsequent studies along with reference strain (S. cerevisiae
HAU-21). The pre-treatments of sugarcane juice (filtration, sterilization and concentration)
prior to fermentation did not increase the alcohol production significantly except concentrated
juice (9.10, 9.23 and 11.12% by RY-5, RY-8 and HAU-21). The ethanol production from
filtered cane juice was slightly better than sterilized sugarcane juice by all the cultures tested.
An inoculum size of 5% and 18h of yeast growth were optimum for ethanol production at
which the concentration of ethanol was 7.99, 8.86 and 9.75% by RY-5, RY-8 and HAU-21
respectively. Yeast recycling upto two cycles gave increased ethanol concentration by all the
cultures while there was a decline in ethanol production after third recycling. An
incubation temperature of 25±2ºC, pH 5.0 and fermentation period of 24h were optimum for
ethanol production by all the cultures. yeast extract (0.3%), peptone (0.5%) and urea (0.3%)
were found best growth factors and nitrogen source for ethanol production from sugarcane
juice by both of yeast isolates. A concentration of 0.2% MgSO4.7H2O, showed maximum
ethanol production by yeast cultures compared to juice alone. Scaling up of cane juice
fermentation upto 5 l. capacity produced 8.20, 9.64 and 11.51% ethanol by RY5, RY8 and
HAU-21. Isolates RY-5 and RY-8 were identified as Saccharomyces sp on the basis of various
morphological and biochemical characteristics.
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Keywords
Fertilizers, Rice, Yields, Grain, Crops, Nitrogen, Planting, Soil analysis, Nutrients, Concentrates