Estimating the distribution of Mixed-Linkage Glucan in sugarcane and its correlation with biomass recalcitrance

Grasses contain abundant mixed-linkage glucan (MLG), a hemicellulosic cell wall polysaccharide with an unbranched beta(1-3)(1-4)-glucan backbone. The deposition of this cell wall component is prevalent in immature tissues, which have low recalcitrance. In order to estimate the distribution of MLG in sugarcane and its correlation with recalcitrance, we examined the composition of sugar cane internodes with varied recalcitrance and lignin content. The hemicellulose composition and MLG content were assessed and the latter was correlated with the efficiency of enzymatic hydrolysis of the samples. Sugarcane internodes from three hybrids were divided into three different stem fractions. Treatment with trifluoroacetic acid (TFA) 15% (v / v) revealed a considerable amount of non-cellulosic glucan in the center of stems (6-11% in pith fractions) that decreases in the rind fraction (1-4%), on the other hand xylan content slightly increases (8-13% in pith; 14% in rinds). A suitable MLG analysis showed that its content is also differentially distributed among different regions. The pith and rind were the fractions with the highest (2-11%) and lowest (0-1%) MLG amount. By enzymatically hydrolyzing these materials without pretreatment it was found that the recalcitrance decreases from center to outer regions (cellulose conversion: 50-86% in piths and 10-38% in rinds, after 72h). Therefore, a correlation could be observed between MLG content and cellulose conversion levels, where high levels of MLG seem to play an important role in promptly hydrolysable biomass materials like sugarcane pith. The differential MLG distribution was also confirmed by immunoblot assays using antibodies against MLG epitopes.