3. Results and discussion
3.1. Isolation and selection of thermotolerant yeast strains
Of various techniques to obtain yeasts capable of growing
and producing ethanol at high temperature, Banat et al.
(1998) stated that isolation from nature was the most successful
technique. Therefore, in this work soil samples from
natural habitat associated with sugar cane were enriched in
sugar cane juice supplemented with 4% (w/v) ethanol and
incubated at 35 C. A total of 72 yeast strains were
obtained. Among these, 37 strains grew satisfactorily even
at 45 C while 18 strains grew only up to 40 C. All of the
strains were then subjected to further screening at various
high temperature levels. Though Banat et al. (1992) used
higher temperatures (45–50 C) for enrichment isolation
and obtained several thermophilic yeast strains capable of
growth at 52 C and ethanol production at 45–50 C, a
lower temperature, 35 C, was used in this study. In order
to obtain yeast strains that tolerated both high temperature
and ethanol, 4% (w/v) ethanol was added to the medium,
for t