Use of Simons’ stain and thermoporometry to track changes in cellulose accessibility after pretreatment and cellulase treatment for poplar and switchgrass

The accessibility of cellulose has been proposed as a key factor in the efficient biological conversion of lignocellulosic biomass to fermentable sugars. In this study, a Simons’ stain (SS) technique along with a differential scanning calorimeter (DSC) based thermoporometry method were used to track changes in cellulose accessibility after pretreatment and cellulase treatment. Dilute acid and autohydrolysis pretreatments were conducted on both poplar and switchgrass at 160 ^oC for 60 min. The cellulose accessibility of these pretreated samples was then characterized by SS and DSC thermoporometry. Results suggested pretreatment significantly increases the accessible surface area (ASA) of substrates so that appreciable amounts of enzyme have access to cellulose and dilute acid pretreatment is much more effective than autohydrolysis. In addition, various substrate factors have been suggested to explain the slowdown in the rate of the incomplete enzymatic hydrolysis of cellulosic materials. In this project, the cellulose accessibility changes for those pretreated poplar and switchgrass during enzymatic hydrolysis were also measured. Samples were taken after different times of hydrolysis, followed by a protease treatment to hydrolyze the remaining cellulases, and then subjected to SS and DSC measurement. The staining results show that the ASA of cellulose increases at the beginning of the hydrolysis, and after reaches its maximum value, start to decrease until the end of hydrolysis. The characterization results obtained here suggested the ASA of the cellulose is an important factor influencing the rate and extent of enzymatic hydrolysis