11-17: The impacts of post-pretreatment strategies on enzyme accessibility and water interactions in alkali pretreated rice straw

Rice straw, a high-abundance lignocellulosic residue from rice production has tremendous potential as a feedstock for biofuel production in California. In this study, we examine the impact of post-alkali pretreatment washing schemes on enzyme saccharification efficiency, particularly focusing on understanding resulting biomass compositional impacts on water interactions with the biomass and enzyme accessibility to the cellulose fraction. Rice straw was pretreated with sodium hydroxide and subsequently washed by two strategies: 1) by extensive washing with DI water to reduce the pH to 5-6; and 2) immediate pH adjustment to pH 5-6 with hydrochloric acid (HCl) before extensive washing with DI water. The two post-pretreatment washing strategies resulted in significant differences in ash and acid-insoluble lignin contents, and saccharification efficiencies. We demonstrate that the differences in saccharification efficiencies are due to differences in the accessibility of the cellulose fraction to the cellulolytic enzymes (as probed with a purified T. reesei Cel7A). We further discuss these results in the context of the mobility of the water associated with the pretreated rice straw processed by the two different strategies (measured by ¹H-Nuclear Magnetic Resonance (NMR)).