Background:
The recalcitrance of lignocellulosic materials is a major drawback for their conversion into fermentable sugars. Lignin depletion in new cultivars or transgenic plants has been identified as a way to diminish this recalcitrance. In this context, a sugarcane breeding program has selected sugarcane plants with low lignin content. The chemical composition and agronomic characteristics of eleven experimental hybrids plus two reference samples are reported. The enzymatic digestion of untreated and chemically delignified samples was evaluated to advance the performance of the sugarcane bagasse in cellulosic-ethanol production processes.
Results:
The glucan, hemicellulose, lignin and extractive contents (based on oven dry biomass) of the experimental hybrids and reference samples varied between 38% and 43%, 25% and 32%, 17% and 24% and 1.6% and 7.5%, respectively. The samples with the smallest amounts of lignin did not present the largest amounts of total polysaccharides. Instead, a flexible distribution of the components, including extractives, seems to compensate for the reduction in lignin content. Hydroxycinnamic acids accounted for a significant part of the aromatic compounds in the samples. P-coumaric acid predominated whereas ferulic acid was detected in low amounts. Hydroxycinnamic acids that were ester-linked to the hemicelluloses varied from 2.3% to 3.6% among the samples. The total amounts of hydroxycinnamic acids that include the fraction linked to lignin through ether linkages varied from 5.0% to 9.2% and correlated, to some extent, with the lignin contents. These clones released up to 31% of glucose after 72h of digestion with commercial cellulases. Chemically delignified samples led to cellulose conversion values higher than 80%. Plants with originally less lignin required lower levels of delignification to reach higher efficiencies of cellulose conversion during the enzymatic treatment.
Conclusion:
Some of the experimental sugarcane hybrids presented combined characteristics of high biomass and sucrose productivities with low lignin contents. Glucan conversion to glucose by commercial cellulases increased in the samples with low lignin content. Chemical delignification further increased the cellulose conversion to values higher than 80%. Interestingly, plants with originally less lignin required lower levels of delignification to reach higher efficiencies of cellulose conversion during the enzymatic treatment.Source:
http://www.biotechnologyforbiofuels.com/rss/