Tuning the molar mass and substitution pattern of complex xylans from corn fibre using subcritical water extraction,Green Chemistry

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Tuning the molar mass and substitution pattern of complex xylans from corn fibre using subcritical water extraction
Green Chemistry ( IF 9.3 ) Pub Date : 2020-11-02 , DOI: 10.1039/d0gc02897e
Reskandi C. Rudjito _{1,

2,

3,

4,

5} , Amparo Jiménez-Quero _{1,

2,

3,

4,

5} , Mahmoud Hamzaoui _{6,

7,

8,

9} , Stéphane Kohnen _{6,

7,

8,

9} , Francisco Vilaplana _{1,

2,

3,

4,

5}

Affiliation

Glucuronoarabinoxylan (GAX) is a structurally complex hemicellulose abundant in the cell wall of corn kernels that constitutes a valuable target for its valorisation from corn processing side streams. However, the crosslinked and recalcitrant nature of corn cell walls hinders its fractionation through mild green processes. In this study, we propose the extraction of GAX using subcritical water, where temperature, pH and time have been optimised to tune the extraction performance (yields and purity of the GAX) and the molecular structure of the extracted GAX (molar mass distribution, substitution pattern and presence of covalently bound phenolic moieties). Higher temperatures under unbuffered conditions caused a prominent drop in pH and autohydrolysis, resulting in a decrease of the molar mass (∼10⁴ Da) and the cleavage of arabinose substitutions. Mitigating the pH drop using mild buffered neutral and alkaline conditions provided higher molar masses of the extracted GAX (∼10⁵ Da), protecting as well the labile arabinose substitutions and resulting in a higher abundance of more complex glycan side chains. Subcritical water extraction preserved the phenolic acid moieties (mainly ferulic acid) covalently bound to polymeric GAX. Several forms of ferulic acid dehydrodimers (di-FA) were detected and identified by liquid chromatography–tandem mass spectrometry (HPLC-LC-MS²) and these di-FAs were particularly enriched in the mild alkaline extracts. We demonstrate that solely by carefully adjusting the operational parameters during subcritical water extraction we can tune the molar mass and complex substitutions of GAX, i.e. the degree and pattern of monomeric and oligomeric glycan side chains and ester-linked phenolic acid substitutions, without the use of additional catalysts. This molecular control over the production of corn GAX can invaluably benefit subsequent development of agroindustry-based biorefineries towards their conversion into novel bio-based materials for food and biomedical applications.

中文翻译：

亚临界水萃取法调节玉米纤维中复杂木聚糖的摩尔质量和取代模式

葡糖醛酸阿拉伯糖基木聚糖（GAX）是一种结构复杂的半纤维素，富含于玉米粒的细胞壁中，构成从玉米加工侧流进行增值的重要靶标。但是，玉米细胞壁的交联和顽固性阻碍了其通过温和的绿色过程进行分级分离。在这项研究中，我们提出了使用亚临界水萃取GAX的方法，其中对温度，pH和时间进行了优化，以调节萃取性能（GAX的产率和纯度）和萃取的GAX的分子结构（摩尔质量分布，取代度）模式和共价结合的酚部分的存在）。在无缓冲条件下较高的温度导致pH值明显下降和自水解，导致摩尔质量降低（〜10 ⁴Da）和阿拉伯糖取代的裂解。使用缓和的中性和碱性缓冲溶液缓解pH下降，可提供更高摩尔质量的提取GAX（〜10 ⁵ Da），并保护不稳定的阿拉伯糖取代基，并产生更多的更复杂的聚糖侧链。亚临界水萃取保留了与聚合GAX共价结合的酚酸部分（主要是阿魏酸）。通过液相色谱-串联质谱法（HPLC-LC-MS ²）检测和鉴定了几种形式的阿魏酸脱氢二聚体（di-FA）），并且这些di-FA尤其富含温和的碱性提取物。我们证明，仅通过在亚临界水萃取过程中仔细调整操作参数，就可以调节GAX的摩尔质量和复杂取代基，即单体和低聚聚糖侧链的程度和模式以及酯连接的酚酸取代基，而无需使用其他催化剂。对玉米GAX生产的这种分子控制可以极大地有利于随后的基于农用生物精炼厂的发展，使其转化为用于食品和生物医学应用的新型生物基材料。

更新日期：2020-11-05

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