3. Results and discussion
3.1. Effect of pretreatment method on physico-chemical properties of
fermentation media
The initial concentration of reducing sugars and dissolved solids
in the fermentation media was the highest in samples after separate
hydrolysis and fermentation (SHF) pretreatment (Fig. 1a and
b respectively). Enzymatic pretreatment using Ceremix 6X MG
preparation resulted in preliminary hydrolysis and liquefaction of
waste bread giving initial content of sugars and dissolved solids
of ca. 25 and 30 g L1 respectively. Other pretreatment methods
applied (microwave and ultrasonic) did not affected initial concentration
of sugars and dissolved solids at the beginning of the fermentation
in comparison to unpretreated variant. The microwave
and ultrasonic pretreatment did not influenced the content of
non-dissolved solids (ca. 131 g kg1 of media) in comparison to
samples without pretreatment (Fig. 1c). Preliminary hydrolysis of
waste bread with Ceremix 6X MG caused reduction in non-dissolved
particles by ca. 80 g kg1 in comparison to control, microwaved
and sonificated samples, while samples after separate
two-stage hydrolysis with a-amylase, glucoamylase and protease
(SHF) contained the lowest amount of non-dissolved solids among
others (ca. 30 g kg1).
Earlier studies shown that different pretreatment methods influence
on the initial properties of fermentation media in the GSHE
aided fermentations. Balcerek and Pielech-Przybylska [22] studied
the effect of thermal prehydrolysis (at 56–57 C) of triticale starch
with a-amylase and non-starch polysaccharide degrading enzyme
on the course of fermentation with GSHE. The initial content of
reducing sugars in pretreated media was much higher in comparison
to samples without prehydrolysis (ca. 11 and 4 g 100 mL1
respectively). Shavanas et al. [21] came to similar conclusion while
studying the effect of preliminary liquefaction of cassava starch
prior to fermentation with GSHE. Similar results were achieved in
present study in samples subjected to enzymatic pretreatment
where the polysaccharides present in the raw material were preliminary
hydrolyzed by the complex of enzymes in Ceremix 6X MG
preparation (amylases, proteases, cellulases and others). The advantage
of using this preparation was previously confirmed in the process
of separate hydrolysis and fermentation of waste bread at high
solids loading [12]. Moreover the content of non-dissolved solids
was much lower in enzymatically pretreated waste bread slurries