Tissue-specific distribution of hemicelluloses in six different sugarcane hybrids as related to cell wall recalcitrance

Abstract

BackgroundGrasses are lignocellulosic materials useful to supply the billion-tons annual requirement for renewable resources that aim to produce transportation fuels and a variety of chemicals. However, the polysaccharides contained in grass cell walls are built in a recalcitrant composite. 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. This complexity usually led to empirically developed pretreatment processes to overcome recalcitrance. A further complication is that efficient pretreatment procedures generally treat the less recalcitrant tissues more than necessary, which results in the generation of undesirable biomass degradation products.ResultsSix different sugarcane hybrids were used as model grasses to evaluate the tissue-specific distribution of hemicelluloses and the role of these components in cell wall recalcitrance. Acetylated glucuronoarabinoxylan (GAX) occurs in all tissues. Mixed-linkage glucan (MLG) was relevant in the innermost regions of the sugarcane internodes (up to 15.4 % w/w), especially in the low-lignin content hybrids. Immunofluorescence microscopy showed that xylans predominated in vascular bundles, whereas MLG occurred mostly in the parenchyma cell walls from the pith region of the hybrids with low-lignin content. 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0513-2) contains supplementary material, which is available to authorized users.

Comparative evaluation of acid and alkaline sulfite pretreatments for enzymatic saccharification of bagasses from three different sugarcane hybrids

“…Both H146 and H89 hybrids presented lower solids yield, but H146 was most susceptible to acid pretreatment, even presenting higher lignin content. Besides the varied compositional characteristics of cultivars, the anatomical structure can influence the pretreatment effectiveness . The highest value for lignin removal was observed for the MB (36.4%), while the lowest was detected for H166 (24%).…”

“…Crystallinity index (CrI) of untreated and pretreated sugarcane bagasse was measured by x‐ray diffraction as described in Costa et al (2016) . The CrI was calculated according to the empirical method developed by Segal et al using the following equation: where I 002 is the maximum intensity of the (002) lattice diffraction and I amorph is the minimum intensity diffraction between the 002 and the 101 peaks.…”

“…Previous studies have shown that the recalcitrance of sugarcane bagasse varies according to the characteristics of different sugarcane varieties (lignin contents, hemicellulose type, and structure) . However, other biomass characteristics such as size and volume of cell wall pores, accessible surface area, and cellulose crystallinity are also relevant factors on the enzymatic hydrolysis of cellulose …”

“…[2][3][4][5][6] However, other biomass characteristics such as size and volume of cell wall pores, accessible surface area, and cellulose crystallinity are also relevant factors on the enzymatic hydrolysis of cellulose. [7][8][9] Various pretreatment methods have been developed to reduce the biomass recalcitrance thus enhancing the accessibility of cellulose. 10 The performance of the pretreatments is also influenced by different sugarcane cultivars since wide variation occurs regarding lignin and hemicellulose contents as well as in the anatomical structure.…”

“…16 Current efforts on sugarcane breeding and genetic engineering have focused on plant characteristics that would result in advantages for certain types of pretreatment technologies. 9,11,16 Most of these pretreatment technologies have focused on the use of autohydrolysis or acid catalyzed processes, requiring new equipment design and test for industrial use in large scale. 3 In contrast, pretreatment processes based on the use of sulfite ions can derive from traditional pulping technologies with robust and tested equipment.…”