The lowest concentration
of ethyl alcohol was found in unpretreated samples
(51.58 g L1), different methods of raw material pretreatment
and the SHF process resulted in higher amount of ethanol by
the end of fermentation (ca. 55–58 g L1). The concentration of
fermentation by-products, glycerol and lactic acid were shown
in Fig. 2b and c respectively. Within the first 24 h of fermentation
yeast did produce ca. 90% of total glycerol in all studied variants
of experiment, however less glycerol was formed in media with
unpretreated and microwaved waste bread than in the case of
other studied methods. The final glycerol concentration was similar
in all studied fermentation media (ca. 6.0–6.5 g L1). The lactic
acid content in fermentation media was similar in all studied
variants of experiment throughout the process (ca. 1 g L1) without
major changes.