According to literature, the ability shown by Saccharomyces spp. to
metabolise the hexoses depends on the temperature and the composition
of culture media (sugars level, D-glucose to D-fructose ratio as well as
ethanol concentration) [10,11]. Since the rate of a substrate conversion
depends on the concentration of the microbial population present in
the reaction medium (CFU/L), an high concentration of lyophilized
yeasts was initially added to the reaction medium so that the great
number of microbial cells could ensure a remarkable conversion of
sugars in all the different operating conditions adopted (Table 1). The
analytical points describing the decrease of concentrations of the two
monosaccharides (D-glucose and D-fructose), and the increase of
the production of ethanol and glycerol as a function of fermentation
time when initial concentrations of 300 gL-1 (1666 mmol L-1) were
used, are reported in Figure 1 (Figure 1a=Saccharomyces cerevisiae;
Figure 1b=Saccharomyces bayanus). The kinetic evolution of hexoses
conversion was described by a first order equation and the following
mathematical form introduced, in the plane (t, [H]):