Biomass enzymatic saccharification is determined by the non-KOH-extractable wall polymer features that predominately affect cellulose crystallinity in corn

Corn is a major food crop with enormous biomass residues for biofuel production. Due to cell wall recalcitrance, it becomes essential to identify the key factors of lignocellulose on biomass saccharification. In this study, we examined total 40 corn accessions that displayed a diverse cell wall composition. Correlation analysis showed that cellulose and lignin levels negatively affected biomass digestibility after NaOH pretreatments at p < 0.05 & 0.01, but hemicelluloses did not show any significant impact on hexoses yields. Comparative analysis of five standard pairs of corn samples indicated that cellulose and lignin should not be the major factors on biomass saccharification after pretreatments with NaOH and H2SO4 at three concentrations. Notably, despite that the non-KOH-extractable residues covered 12%-23% hemicelluloses and lignin of total biomass, their wall polymer features exhibited the predominant effects on biomass enzymatic hydrolysis including Ara substitution degree of xylan (reverse Xyl/Ara) and S/G ratio of lignin. Furthermore, the non-KOH-extractable polymer features could significantly affect lignocellulose crystallinity at p < 0.05, leading to a high biomass digestibility. Hence, this study could suggest an optimal approach for genetic modification of plant cell walls in bioenergy corn.

玉米是一类主要粮食作物，其副产物包含巨量生物质残渣，可用于生物燃料生产。受细胞壁抗降解性（cell wall recalcitrance）制约，亟需明确木质纤维素（lignocellulose）在生物质糖化（biomass saccharification）过程中的关键调控因子。本研究共考察了40份具有多样细胞壁组成的玉米种质资源（corn accessions）。相关性分析结果显示，经氢氧化钠（NaOH）预处理后，纤维素与木质素含量对生物质可糖化性具有显著负向影响（p < 0.05及p < 0.01），但半纤维素对己糖产率无显著作用。对5组标准玉米对照样品的比较分析表明，在三种浓度梯度的氢氧化钠与硫酸（H₂SO₄）预处理后，纤维素与木质素并非影响生物质糖化的核心因子。值得注意的是，尽管不溶于氢氧化钾（KOH）的残渣占总生物质中半纤维素与木质素组分的12%~23%，但其细胞壁聚合物的结构特征对生物质酶解水解具有主导调控作用，包括木聚糖的阿拉伯糖（Ara）取代度（以反向木糖/阿拉伯糖比值，Xyl/Ara，表征）以及木质素的S/G比值（syringyl/guaiacyl）。此外，不溶于KOH的聚合物结构特征可显著影响木质纤维素结晶度（p < 0.05），进而提升生物质酶解糖化效率。综上，本研究可为能源玉米的植物细胞壁遗传改良提供最优策略参考。