Exploring the effect of different plant lignin content and composition on ionic liquid pretreatment efficiency and enzymatic saccharification of Eucalyptus globulus L. mutants

There are several approaches being investigated to improve the efficiency of biomass conversion into fermentable sugars, including those that engineer the feedstocks to enhance digestibility. In this study it was evaluated the impact of genotype modifications of three mutants of Eucalyptus globulus L., and of the corresponding wild type on cellulose hydrolyzability before and after ionic liquid (IL) pretreatment. Both untreated and IL-treated samples were chemically characterized and tested for cellulose hydrolizability. Results obtained indicate that genetic modifications altered wood lignin-S/G ratio. This alteration resulted in a different hydrolyzability of cellulose for untreated samples, i.e. high lignin-S/G ratio produced low glucose yield (r= -0.97; P< 0.03; n= 4), but did not affect glucose yield after IL pretreatment. IL pretreated samples had increased glucose yields compared to that of untreated samples due to the modification of microcrystalline cellulose I to mixtures of more hydrolysable cellulose II and amorphous cellulose, and to the partial removal of the steric impediment, or removal of the lignin "sheath" protecting cellulose, to enzymes. The efficiency of the IL pretreatment used in this study does not appear to be affected by the S/G content of the E. globulus.