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Sweet sorghum is an attractive feedstock for ethanol production. The juice extracted from the fresh stem is composed of sucrose, glucose, and fructose and can therefore be readily fermented to alcohol. The solid fraction left behind, the so-called bagasse, is a lignocellulosic residue which can also be processed to ethanol. The objective of our work was to test sweet sorghum, the whole crop, as a potential raw material of ethanol production, i.e., both the extracted sugar juice and the residual bagasse were tested. The juice was investigated at different harvesting dates for sugar content. Fermentability of juices extracted from the stem with and without leaves was compared. Sweet sorghum bagasse was steam-pretreated using various pretreatment conditions (temperatures and residence times). Efficiency of pretreatments was characterized by the degree of cellulose hydrolysis of the whole pretreated slurry and the separated fiber fraction. Two settings of the studied conditions (190 degrees C, 10 min and 200 degrees C, 5 min) were found to be efficient to reach conversion of 85-90%.

Conversion of lignocellulosic substrates is limited by several factors, in terms of both the enzymes and the substrates. Better understanding of the hydrolysis mechanisms and the factors determining their performance is crucial for commercial lignocelluloses-based processes. Enzymes produced on various carbon sources (Solka Floc 200, lactose and steam-pre-treated corn stover) by Trichoderma reesei Rut C30 were characterised by their enzyme profile and hydrolytic performance. The results showed that there was a clear correlation between the secreted amount of xylanase and mannanase enzymes and that their production was induced by the presence of xylan in the carbon source. Co-secretion of alpha-arabinosidase and alpha-galactosidase was also observed. Secretion of beta-glucosidase was found to be clearly dependent on the composition of the carbon source, and in the case of lactose, 2-fold higher specific activity was observed compared to Solka Floc and steam-pre-treated corn stover. Hydrolysis experiments showed a clear connection between glucan and xylan conversion and highlighted the importance of beta-glucosidase and xylanase activities. When hydrolysis was performed using additional purified beta-glucosidase and xylanase, the addition of beta-glucosidase was found to significantly improve both the xylan and glucan conversion.

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a b s t r a c tEnzymatic hydrolysis of lignocellulosic substrates is one of the limiting steps in second generation bioethanol production. The effects of addition of poly(ethylene glycol) 4000 (PEG) on the efficiency and adsorption of cellulase components during the 72-h hydrolysis of steam-pretreated spruce were investigated. It was found that addition of PEG increased the amount of the enzyme components in the hydrolysis supernatant to varying degrees. As an effect of PEG addition the concentration of free proteins increased by 36% and the free overall cellulolytic activity (FPA) in the liquid fraction by 51%. After 72-h hydrolysis with PEG 48-68% higher activities towards 4-methylumbelliferyl-saccharide substrates were recovered. The results suggest that the effect of PEG is based on the decrease of non-productive enzyme binding. The structure of the hydrolysis residues was studied by 31 P NMR.