11-06: Varied recalcitrance in sugar cane hybrids with contrasting lignin contents

Lignin depletion in new cultivars or transgenic plants has been identified as a way to diminish the recalcitrance of lignocellulosic materials. In eleven sugarcane hybrids and two reference samples described here, the glucan, hemicellulose, lignin and extractive contents varied between 38-43%, 25-32%, 17-24% and 2-8%, respectively. The total amounts of hydroxycinnamic acids that include the ester-linked and the ether-linked fractions coupled to lignin varied from 5 to 9% and correlated, to some extent, with the lignin contents. Cellular UV-microspectrophotometric analyses of selected samples showed that vessels presented the most lignified cell walls, followed by fibers and parenchyma. The pith region, rich in parenchyma cells, was characterized by a very low recalcitrance. Enzymatic digestion of the whole untreated sugarcane bagasse originating from the plants with high lignin contents was limited to 20% of cellulose conversion in 72h of hydrolysis. Such conversion increased to 31% in the hybrid with the lowest lignin content. Selective delignification of the samples further increased the cellulose conversion to values higher than 80%. Plants with originally less lignin required less delignification to reach higher efficiencies of cellulose conversion. In alkaline-sulfite pretreated materials, the removal of approximately 50% of lignin and 30% of hemicellulose improved the cellulose hydrolysis to 85% after 96h of reaction. At a shorter hydrolysis time of 24h, 50% of the cellulose was hydrolyzed, efficiency that was increased to 64% in a hybrid with lower lignin content. Compiled data suggest possible benefits of using samples with low lignin contents during biomass processing