Abstract
BackgroundWheat straw used for bioethanol production varies in enzymatic digestibility according to chemical structure and composition of cell walls and tissues. In this work, the two biologically different wheat straw organs, leaves and stems, are described together with the effects of hydrothermal pretreatment on chemical composition, tissue structure, enzyme adhesion and digestion. To highlight the importance of inherent cell wall characteristics and the diverse effects of mechanical disruption and biochemical degradation, separate leaves and stems were pretreated on lab-scale and their tissue structures maintained mostly intact for image analysis. Finally, samples were enzymatically hydrolysed to correlate digestibility to chemical composition, removal of polymers, tissue composition and disruption, particle size and enzyme adhesion as a result of pretreatment and wax removal. For comparison, industrially pretreated wheat straw from Inbicon A/S was included in all the experiments.ResultsWithin the same range of pretreatment severities, industrial pretreatment resulted in most hemicellulose and epicuticular wax/cutin removal compared to lab-scale pretreated leaves and stems but also in most re-deposition of lignin on the surface. Tissues were furthermore degraded from tissues into individual cells while lab-scale pretreated samples were structurally almost intact. In both raw leaves and stems, endoglucanase and exoglucanase adhered most to parenchyma cells; after pretreatment, to epidermal cells in all the samples. Despite heavy tissue disruption, industrially pretreated samples were not as susceptible to enzymatic digestion as lab-scale pretreated leaves while lab-scale pretreated stems were the least digestible.ConclusionsDespite preferential enzyme adhesion to epidermal cells after hydrothermal pretreatment, our results suggest that the single most important factor determining wheat straw digestibility is the fraction of parenchyma cells rather than effective tissue disruption.
Highlights
Wheat straw used for bioethanol production varies in enzymatic digestibility according to chemical structure and composition of cell walls and tissues
This phenomenon has been reported in fractionated poplar (Populus tremoloides Michx.) [35] and wheat straw [36] where the amounts of lignin were significantly increased after treatment
Our results showed increased enzyme adhesion to epidermal cells after hydrothermal pretreatment but no increase in conversion yields upon dewaxing; perhaps the fraction of epidermal cells is too small to influence the overall sugar yield
Summary
Wheat straw used for bioethanol production varies in enzymatic digestibility according to chemical structure and composition of cell walls and tissues. The two biologically different wheat straw organs, leaves and stems, are described together with the effects of hydrothermal pretreatment on chemical composition, tissue structure, enzyme adhesion and digestion. Samples were enzymatically hydrolysed to correlate digestibility to chemical composition, removal of polymers, tissue composition and disruption, particle size and enzyme adhesion as a result of pretreatment and wax removal. Vascular bundles consist of xylem (tracheids) and phloem (sieve tube elements) and are supported by sclerenchyma tissue (fibers) in stems. Tracheids and fibers both have thickened and often lignified secondary walls. Dermal tissues and silicates together provide rigidity and protection from degradation by weather conditions, water loss, microbes and insects etc. [14,15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
