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Improved analysis of arabinoxylan-bound hydroxycinnamate conjugates in grass cell walls
Biotechnology for Biofuels ( IF 6.3 ) Pub Date : 2020-12-10 , DOI: 10.1186/s13068-020-01841-6
Alexis Eugene , Catherine Lapierre , John Ralph

Arabinoxylan in grass cell walls is acylated to varying extents by ferulate and p-coumarate at the 5-hydroxy position of arabinosyl residues branching off the xylan backbone. Some of these hydroxycinnamate units may then become involved in cell wall radical coupling reactions, resulting in ether and other linkages amongst themselves or to monolignols or oligolignols, thereby crosslinking arabinoxylan chains with each other and/or with lignin polymers. This crosslinking is assumed to increase the strength of the cell wall, and impedes the utilization of grass biomass in natural and industrial processes. A method for quantifying the degree of acylation in various grass tissues is, therefore, essential. We sought to reduce the incidence of hydroxycinnamate ester hydrolysis in our recently introduced method by utilizing more anhydrous conditions. The improved methanolysis method minimizes the undesirable ester-cleavage of arabinose from ferulate and p-coumarate esters, and from diferulate dehydrodimers, and produces more methanolysis vs. hydrolysis of xylan-arabinosides, improving the yields of the desired feruloylated and p-coumaroylated methyl arabinosides and their diferulate analogs. Free ferulate and p-coumarate produced by ester-cleavage were reduced by 78% and 68%, respectively, and 21% and 39% more feruloyl and p-coumaroyl methyl arabinosides were detected in the more anhydrous method. The new protocol resulted in an estimated 56% less combined diferulate isomers in which only one acylated arabinosyl unit remained, and 170% more combined diferulate isomers conjugated to two arabinosyl units. Overall, the new protocol for mild acidolysis of grass cell walls is both recovering more ferulate- and p-coumarate-arabinose conjugates from the arabinoxylan and cleaving less of them down to free ferulic acid, p-coumaric acid, and dehydrodiferulates with just one arabinosyl ester. This cleaner method, especially when coupled with the orthogonal method for measuring monolignol hydroxycinnamate conjugates that have been incorporated into lignin, provides an enhanced tool to measure the extent of crosslinking in grass arabinoxylan chains, assisting in identification of useful grasses for biomass applications.

中文翻译:

改善草细胞壁中结合阿拉伯木聚糖的羟基肉桂酸酯共轭物的分析

通过在木聚糖主链上分支的阿拉伯糖基残基的5-羟基位置上的阿魏酸酯和对香豆酸酯,草细胞壁中的阿拉伯木聚糖被不同程度地酰化。这些羟基肉桂酸酯单元中的一些然后可能参与细胞壁自由基偶联反应,从而在它们之间或与单木质醇或寡聚醇之间产生醚和其他键,从而使阿拉伯木聚糖链彼此和/或与木质素聚合物交联。假定这种交联增加了细胞壁的强度,并阻碍了自然和工业过程中草类生物质的利用。因此,用于定量各种草组织中的酰化程度的方法是必不可少的。我们试图通过利用更多的无水条件来减少我们最近引入的方法中羟基肉桂酸酯水解的发生率。改进的甲醇分解方法将阿魏糖从阿魏酸酯和对香豆酸酯和二价脱氢二聚体的不希望有的酯裂解减至最小,与木聚糖-阿拉伯糖苷的水解相比,产生了更多的甲醇分解作用,从而提高了所需阿魏酸酯化和对香豆酸酯化的阿拉伯阿拉伯糖苷的收率。及其分散的类似物。通过酯裂解产生的游离阿魏酸酯和对香豆酸酯分别减少了78%和68%,而在更无水的方法中,检测到的阿魏酸酯和对香豆酰甲基阿拉伯糖苷分别多了21%和39%。新方案导致其中仅保留一个酰化的阿拉伯糖基单元的组合的二羟基异构体的估计减少了56%,并且与两个阿拉伯糖基单元结合的组合的二羟基异构体的组合的估计多了170%。总体,轻度酸解草细胞壁的新方案是从阿拉伯木聚糖中回收更多的阿魏酸和对香豆酸酯-对-阿拉伯糖缀合物,然后将其中的更少裂解成游离的阿魏酸,对香豆酸,并仅用一种阿拉伯糖基酯进行脱水脱氢。这种更清洁的方法,尤其是与正交测量方法结合使用时,该方法用于测量已掺入木质素的单木香醇羟基肉桂酸酯共轭物,提供了一种增强的工具来测量草木聚糖链中的交联程度,有助于鉴定可用于生物质应用的草。
更新日期:2020-12-11
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