FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY




Utilization of waste bread for bioethanol production


The objective of the research study was to assess the technological usefulness of highly mouldcontaminated waste wheat-rye bread as a raw material in the production of bioethanol. The research material was a waste wheat rye-bread (returned by shops after the expiration of its shelf life) showing superficial mould contamination spots. Waste bread fermentation media were produced using a mashing procedure based on an energy-saving pressure-less starch release method. The obtained mashes containing 28 (I), 32 (II), and 36 (III) [% (w/w)] of the raw material were inoculated with Saccharomyces cerevisiae Ethanol Red yeast and fermented using a periodic method. Determined were the dynamics of fermentation, carbohydrate profiles of the mashes (by a HPLC method), and changes in the concentration rate of substrates and in the quantity of metabolites (ethanol, glycerol, succinic acid, and ethanoic acid) produced during the fermentation process. The physiological condition of yeast cells was evaluated prior to and after the fermentation using a microscopic technique. On the basis of the results obtained, the yield parameters of the ethanol fermentation process were computed and the technological usefulness of the raw material studied was assessed. It was found that the fermentation process of mashes lasted 68 h regardless of the quantity of raw material therein. The mashes containing 32 % of raw material showed the best process dynamics. The initial concentration rate of sugars (glucose, maltose, and maltotriose) was higher in the mashes with a higher content of raw material. During the fermentation, the yeast utilized almost all of the carbohydrates available. In the fermentation liquids, typical fermentation by-products were found (glycerol, succinic acid, and acetic acid). The highest concentration rate of glycerol (14.56 g/l) was determined in the sample containing 36 % of raw material (III). The concentration rate of ethanol produced by the yeast in the media studied was 60.7 g/l (I), 72.7 g/l (II), and 83.1 g/l (III). The highest process yield (ca. 70 %) was obtained while fermenting mashes containing 32 and 36 % of raw material. After the fermentation completed, the yeasts used were characterized by a higher content of inactive cells compared to the initial biomass. Based on the results obtained, it was concluded that the optimal content of wheat-rye bread in the mash was 32 %.


wheat-rye bread, mash, fermentation, bioethanol