| The efficiency of cellulose hydrolysis under straight saccharification and simultaneous saccharification and fermentation (SSF) conditions was evaluated using three lignocellulosic materials (switchgrass, cornstover, and poplar), which had been pretreated with dilute sulfuric acid under conditions which optimized xylose concentrations in the prehydrolysate liquid. Yields of glucose, cellobiose and ethanol obtained from the pretreated feedstocks were measured over 168 hrs. The final theoretical conversions of cellulose from pretreated switchgrass, cornstover, and poplar in straight saccharification were 85-100% (average 94%), 84-100% (average 96%), and 75-100% (average 87%), respectively, while in SSF the conversions were 84-90% (average 87%), 91-96% (average 90%), 72-82% (average 76%), respectively. The conversion rates of poplar in straight saccharification and SSF were significantly lower than those of switchgrass and cornstover. The effects of reaction parameters such as enzyme activity, cellulose availability, and yeast cell viability on the extent of hydrolysis in straight saccharification and SSF were also studied. Results indicate that the lower glucose or ethanol yields associated with some of the poplar were due to the recalcitrant nature of its cellulose.; To compare accurately the efficiencies between straight saccharification and SSF, a direct method for determining the cellulose content of the feedstocks residues resulting from SSF experiments has been developed and evaluated. The method improves on classical cellulose assays by incorporating a yeast lysing enzyme to remove yeast glucans from the feedstocks residue prior to acid hydrolysis and subsequent quantification of cellulose derived glucose. A freeze-drying step was identified as necessary to render the SSF yeast cells susceptible to enzyme lysis. The method was applied to the analysis of the cellulose and yeast-glucan content of SSF residues from the three pretreated feedstocks. Cellulose assays employing the lysing enzyme preparation demonstrated relative errors up to 7.2% when yeast-associated glucan were not removed prior to analysis of SSF residues. Enzymatic lysis of SSF yeast cells may be viewed as a general preparatory procedure to be used prior to the subsequent chemical and physical analysis of SSF residues. |
