Evaluation of physicochemical preservation techniques for the storage of sugar beet molasses followed by bioethanol production

Abstract

For many biorefinery processes, the development of effective preservation techniques is essential to avoid any sugar loss between crop-harvesting and fermentation. In this work, five physicochemical techniques (acidification, ozonation, addition of sodium hydrosulfite, sodium sulfate and oil layer) were investigated for the preservation of sugar beet molasses diluted at low (150 g/L) and high (300 g/L) concentration of initial sugars. After 30 days, sugars and metabolites profiles were quantified to determine the optimal preservation technique capable of limiting the biological contamination while preserving as much fermentable sugars as possible. Although none of the strategies was efficient to prevent the microbial contamination at 150 g/L, some approaches allowed preserving more than 90% of fermentable sugars at 300 g/L of initial sugars. Furthermore, the use of 2 g/L of sodium hydrosulfite or acidifying the media to pH 3 allowed the conservation of nearly 100% of the fermentable sugars. Fermentation assays performed after storage indicated that acidification, sodium hydrosulfite and ozonation did not alter the fermentation performances, as the production of ethanol reached 102 g/L after 6 days of incubation. Therefore, the use of sodium hydrosulfite or acidification were considered as relevant strategies for maintaining fermentable sugars in liquid feedstock for bioethanol production.