4. Conclusions
Argentine molasses and grapes were used to isolate 29 ethanolproducing
yeasts, finding three isolates with higher ability to produce
ethanol. One of these isolates showed a homogeneous growth
(A2) meanwhile the other two presented a flocculent growth (A10
and A11) when they were grown in commercial media. It was also
observed that the three isolates presented a percentage of similarity
of 100% with the strain S. cerevisiae. The three strains were
highly sensitive to changes in temperature, finding an optimal
temperature for the production of ethanol at 30 C, and although
they could tolerate up to 300 g/L without decreasing the production
of ethanol, the best results were achieved using 250 g/L of initial
sugar. Higher sugars concentrations (350 g/L) represented a
decrease in ethanol concentration, particularly using the non-
flocculent strain A2, thus concluding that flocculation can act as a
protective mechanism in yeast stress conditions such as with high
concentration of sugars, and consequently the flocculent characteristics
of strains A10 and A11 protected a high osmotic pressure
generated by high sugar concentration. These strains were also able
to grow in molasses medium although the behavior of the non-
flocculent A2 strain was faster, probably because of its dispersed
form facilitates the transfer of nutrients and products. The process
can be successfully scaled up from laboratory scale to 10L bioreactor,
thus demonstrating the feasibility of the S. cerevisiae A2 strain
to be used as a novel strain to produce ethanol.