Cell wall structural changes in wheat straw pretreated for bioethanol production

TLDR

Pretreatment is essential for enzymatic hydrolysis and bioethanol production, and recent work shows that a mild, hydrothermal process without added chemicals is sufficient and effective for wheat straw. The study aims to characterize how hydrothermal pretreatment alters wheat straw cell‑wall components to explain its improved digestibility. Microscopic (AFM, SEM) and spectroscopic (ATR‑FTIR) analyses were used to examine cellulose, lignin, hemicellulose, and wax distribution, revealing lignin re‑localization without cellulose fibril degradation. Pretreatment removes wax and partially removes hemicellulose, relocalizes lignin, and increases cellulose accessibility, thereby enhancing digestibility without disrupting the cell wall.

Abstract

Pretreatment is an essential step in the enzymatic hydrolysis of biomass and subsequent production of bioethanol. Recent results indicate that only a mild pretreatment is necessary in an industrial, economically feasible system. The Integrated Biomass Utilisation System hydrothermal pretreatment process has previously been shown to be effective in preparing wheat straw for these processes without the application of additional chemicals. In the current work, the effect of the pretreatment on the straw cell-wall matrix and its components are characterised microscopically (atomic force microscopy and scanning electron microscopy) and spectroscopically (attenuated total reflectance Fourier transform infrared spectroscopy) in order to understand this increase in digestibility.The hydrothermal pretreatment does not degrade the fibrillar structure of cellulose but causes profound lignin re-localisation. Results from the current work indicate that wax has been removed and hemicellulose has been partially removed. Similar changes were found in wheat straw pretreated by steam explosion.Results indicate that hydrothermal pretreatment increases the digestibility by increasing the accessibility of the cellulose through a re-localisation of lignin and a partial removal of hemicellulose, rather than by disruption of the cell wall.