Ethanol fermentation of waste bread using granular starch hydrolyzing enzyme: Effect of raw material pretreatment

The subject of this research project was assessment of direct starch to ethanol conversion process course of waste wheat-rye bread using granular starch hydrolyzing enzyme (GSHE). Several pretreatment methods (enzymatic prehydrolysis, microwave irradiation, sonification) were used to improve the course of fermentation and were compared with separate hydrolysis and fermentation (SHF). Due to high water binding capacity of raw material fermentations were conducted at a substrate loading of 150 g kg−1. Only during enzymatic pretreatment and the SHF process the raw material was preliminary liquefied so its higher concentrations could be applied. The dynamics of fermentation was similar in all studied variants. The fermentation of unpretreated waste bread ended with 80.00% ethanol yield (354.36 g kg−1 of raw material). Pretreatment of raw material improved ethanol yield by ca. 3–8%.