Wheat Pretreatment Factors Affecting Fermentable Monosaccharide Yields for Bioethanol Production

Researchers from the Department of Chemical and Biochemical Engineering, Technical University of Denmark, investigated the interactive effects of pretreatment pH, temperature and reaction time on the subsequent monosaccharide yields (glucose, xylose) of mildly pretreated wheat straw. In the production of biofuel ethanol from lignocellulosic biomass, such as wheat straw, the material undergoes three processing stages: (1) pretreatment to remove the tight lignin wrapping in the biomass; pretreatment liberates/exposes the carbohydrate molecules within the biomass, (2) enzymatic treatment (also called "enzymatic saccharification") to break-down the carbohydrate molecules into component monosaccharides (mainly glucose and xlose), and (3) fermentation of the component monsaccharides to ethanol.

Pretreatment has been identified as a crucial process among these three processes, because it determines how much of the carbohydrates are available for enzymatic saccharification and fermentation. Pretreatment methods include additions of acid, alkali and oxidizing agents, in combination with heat. The pH, temperature, and reaction time usually determine the performance of a particular pretreatment in terms of the subsequent monoscaccharide yields.

The Danish researchers conducted statistical experimental designs in order to investigate the interplay of pH, temperature and time during wheat straw pretreatment. They found that at temperatures below 140 degrees Celsius and a reaction time of about 10 minutes, alkaline pretreatment pH was better in preparing for enzymatic release of both xylose and glucose than acid pretreatment pH.

Acid pretreatment was found to cause the solubilization of the hemicellulose fraction of the biomass, and liberates the 5-carbon monoscaccharides (xylose) into the liquid fraction; this reduces the available carbohydrates for ethanol processing in the pretreated solid biomass.

The full study is published in the free access journal, Biotechnology for Biofuels (URL above).