Abstract
Sugar beet pulp, a byproduct of sugar beet processing, can be used as a feedstock in second-generation ethanol production. The objective of this study was to investigate the effects of pretreatment, of the dosage of cellulase and hemicellulase enzyme preparations used, and of aeration on the release of fermentable sugars and ethanol yield during simultaneous saccharification and fermentation (SSF) of sugar beet pulp-based worts. Pressure-thermal pretreatment was applied to sugar beet pulp suspended in 2% w/w sulphuric acid solution at a ratio providing 12% dry matter. Enzymatic hydrolysis was conducted using Viscozyme and Ultraflo Max (Novozymes) enzyme preparations (0.015–0.02 mL/g dry matter). Two yeast strains were used for fermentation: Ethanol Red (S. cerevisiae) (1 g/L) and Pichia stipitis (0.5 g/L), applied sequentially. The results show that efficient simultaneous saccharification and fermentation of sugar beet pulp was achieved. A 6 h interval for enzymatic activation between the application of enzyme preparations and inoculation with Ethanol Red further improved the fermentation performance, with the highest ethanol concentration reaching 26.9 ± 1.2 g/L and 86.5 ± 2.1% fermentation efficiency relative to the theoretical yield.
Highlights
Sugar beet is grown and processed in all countries of the European Union and plays an important role in sustaining jobs and local economies in many rural areas
Efficient hydrolysis and fermentation depend on the type of pretreatment, the conditions of enzymatic hydrolysis, and the microorganisms used for the fermentation of released hexose and pentose sugars
Earlier research had demonstrated that conducting separate enzymatic hydrolysis of sugar beet pulp at elevated temperatures for 48 hours increased the cost of the process and the risk of microbial infection, thereby lowering fermentation performance
Summary
Sugar beet is grown and processed in all countries of the European Union (with the exception of Luxembourg) and plays an important role in sustaining jobs and local economies in many rural areas. Byproducts from the processing of sugar beet include beet leaves and sugar beet pulp. One ton of sugar beet yields on average 160 kg of sugar, 500 kg of wet pulp, and 38 kg of molasses. The exhausted beet material, which remains after diffusion with hot water to draw the sugar from the beets, is called pulp. It is usually pressed and/or dried for animal feed [2]. Annual production of beet pulp in the EU amounts to around 8 million tons of pressed and 5.5 million tons of dried product [1]
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