We found that fructose causes a dramatic decrease in the
tolerance level and survival rate of all the yeasts tested, Saccharomyces
and non-Saccharomyces, a finding that to our knowledge has
not been reported before, as usually tolerance/resistance determinations
in the literature are carried out using solely glucose as
the carbon source. Accordingly, there is a high risk of overestimation
of ethanol tolerance of a given strain when tested in the
laboratory using only glucose, when it is intended for performing
fermentation in fructose-rich substrates. The methodology and
analysis procedure proposed here for stress tolerance quantification
applied to several genera of yeasts is proposed for screening
and selection of those strains with a high performance on
fermentation processes, but also could be used as a tool for isolation
of those variants/segregants of a yeast/bacteria population with a
more resistant phenotype, allowing a direct calculation of the ratio
of this subpopulation from the original sample.