Tissue-specific distribution of lignin and hemicelluloses in sugarcane hybrids presenting varied recalcitrance

Grasses are lignocellulosic materials useful to supply the billion-tons annual requirement for renewable resources that aims to produce transportation fuels and a variety of chemicals. However, deconstruction of these cell walls is still a challenge for the energy-efficient and economically viable transformation of lignocellulosic materials. The varied tissue-specific distribution of cell wall components adds complexity to the origins of cell wall recalcitrance in grasses. In this work, sugarcane hybrids were evaluated regarding the tissue-specific distribution of macromolecular components. Lignin predominated in fiber and vessel cell walls, whereas in parenchyma cells the main aromatic components were hydroxycinnamic acids. In addition to cellulose, acetylated glucuronoarabinoxylan (GAX) predominates in all tissues. Mixed-linkage glucan (MLG) was relevant in the parenchyma cell walls of the innermost regions of the sugarcane internodes (up to 15.4 % w/w), especially in the low-lignin content hybrids. Evaluation of the digestibility of sugarcane polysaccharides by commercial enzymes indicated that the cell wall recalcitrance varied considerably along the internode regions and in the sugarcane hybrids. Pith regions of the hybrids with high MLG and low lignin contents reached up to 85% cellulose conversion after 72 h of hydrolysis, without any pretreatment. The collective characteristics of the internode regions were related to the varied recalcitrance found in the samples. Components such as lignin and GAX were critical for the increased recalcitrance, but low cellulose crystallinity index, high MLG contents and highly substituted GAX contributed to the generation of a less recalcitrant material.