Simultaneous saccharification and ethanol fermentation of waste wheat–rye bread at very high solids loading: Effect of enzymatic liquefaction conditions

• Simultaneous saccharification and fermentation of waste bread at high solids.
• Enzymatic liquefaction was modified on the basis of substrate thermal properties.
• Lower liquefaction temperature decreased hydrolysis efficiency.
• The highest ethanol yield obtained for substrate liquefaction at 59 °C.

The aim of this research was to investigate the ethanol fermentation process course and yield from waste wheat–rye bread in the simultaneous saccharification and fermentation (SSF) conditions at high solids loading (300 g kg−1). Moreover the enzymatic liquefaction conditions were modified on the basis of thermal properties of starch and compared to the temperature optimal for α-amylase activity (85 °C). The liquefaction of raw material at modified conditions decreased the hydrolysis efficiency in comparison to hydrolysis at 85 °C. The course and ethanol yield of the SSF process in the optimized conditions of liquefaction was comparable or even higher in comparison to standard conditions. The best results were obtained when starch was liquefied at the final temperature of gelatinization (59 °C) resulting in final ethanol concentration of 128.01 g L−1 yielding 425.04 g kg−1 of dry matter and 95.93% practical yield (416.09 g kg−1 and 93.91% for liquefaction at 85 °C).