0.5 g L1. In the SHF variant of experiment yeast did consume half
of the available sugars in the fermentation feed after 24 h of the
process and almost all available sugars after subsequent days.
HPLC analysis of carbohydrates in media during the fermentation
also shown that almost all available glucose was utilized by yeast
by the second day of the process (Table 1). The content of maltotriose
throughout the fermentation was below 1 g L1 regardless
from the experimental variant. The dextrins were not completely
hydrolyzed and eventually utilized by yeast by the end of fermentation,
however its concentration decreased between the
24th and 48th hour and did not significantly change by the end
of the process. The changes in dissolved solids in the fermentation
media were similar to changes in the concentration of reducing
sugars in particular variants of experiment (Fig. 1b). The nondissolved
solids content after the first day of fermentation was
similar in all studied variants of experiment (ca. 30 g kg1) and
it did not significantly change by the end of the process
(Fig. 1c). The changes in ethanol formation during fermentation
tests were shown in Fig. 2a. It was observed that within the first
24 h of fermentation of enzymatically pretreated waste bread
with GSHE and separate hydrolysis and fermentation variant,
yeast produced the highest amount of ethanol (ca. 43.5 g L1).
Lower concentration of ethanol (ca. 38.8 g L1) was found after
the same time in unpretreated and sonificated waste bread samples,
while the lowest amount of alcohol (ca. 32.6 g L1) was
determined in media with subsequently microwave irradiated
waste bread. The production of ethanol by yeast in studied fermentation
tests lasted by the second day of the process and did
not significantly change by the third day.