Characterization of cell wall components of wheat bran following hydrothermal pretreatment and fractionation

Abstract

BackgroundPretreatments are a prerequisite for enzymatic hydrolysis of biomass and production of ethanol. They are considered to open up the plant cell wall structure by altering, moving or solubilizing lignin and hydrolyzing a proportion of hemicellulosic moieties. However, there is little information concerning pretreatment-induced changes on wheat bran cell wall polymers and indeed on changes in cell wall phenolic esters in bran or other lignocellulosic biomass. Here, we evaluate polymeric changes (chemical and physical) as a result of selected hydrothermal pretreatment conditions on destarched wheat bran using controlled polymer extraction methods. Quantification of cell wall components together with soluble oligosaccharides, the insoluble residues and ease of extractability and fractionation of biomass residues were conducted.ResultsPretreatment solubilized selected arabinoxylans and associated cross-linking ferulic and diferulic acids with a concomitant increase in lignin and cellulosic glucose. The remaining insoluble arabinoxylans were more readily extractable in alkali and showed considerable depolymerization. The degree of arabinose substitution was less in xylans released by higher concentrations of alkali. The recalcitrant biomass which remained after pretreatment and alkali extraction contained mostly cellulosic glucose and Klason lignin. Pretreatment generated small but insignificant amounts of yeast-inhibiting compounds such as furfural and hydroxymethyl furfural.As such, simultaneous saccharification and fermentation of the hydrothermally pretreated bran resulted in increased ethanol yields compared to that of the control (97.5% compared to 63% theoretical).ConclusionHydrothermal pretreatment of destarched wheat bran resulted in degradation and depolymerization of the hemicellulosic arabinoxylans together with some breakdown of cellulosic glucose. This was accompanied by a significant reduction in the cross-linking phenolic acids such as ferulic and diferulic acids. The results suggest that hydrothermal pretreatment enhances enzymatic digestibility of the cellulose not only by depolymerization and solubilization of the hemicelluloses but by breakdown of interpolymeric phenolic cross-links between the remaining insoluble polymers. This allows easier access of hydrolytic enzymes by opening or loosening of the cell wall thus resulting in enhanced saccharification of cellulose and subsequent fermentation to ethanol. The reduction in cinnamic acids by selected breeding or biotechnological approaches could provide a useful basis for improved saccharification and fractionation of wheat bran polysaccharides.

Dietary Fiber Extraction from Defatted Corn Hull by Hot-Compressed Water

“…Cellulose is a polymer of glucose, however, unlike starch, the specifi c structure of cellulose favors the ordering of the polymer chains into tightly packed, highly crystalline structures, which are water-insoluble and difficult to de-polymerize [Gáspár et al, 2007]. The other carbohydrate component in corn fi ber is mostly hemicellulose, which is a well-branched polymer of xylose substituted with galactose, mannose, arabinose, and glucose [Peng et al, 2012;Merali et al, 2015]. The content of water-soluble hemicelluloses in corn fi ber was important to estimate the effect of corn fi ber supplementation on the inhibition of harmful metabolite production in the gut, because harmful enzyme activities and metabolites were decreased by both corn fi ber and hemicelluloses supplementation [Sugawara et al, 1989;1990, 1991a.…”

Processing, Valorization and Application of Bio-Waste Derived Compounds from Potato, Tomato, Olive and Cereals: A Review

“…Recently, steam explosion-assisted extraction was found to be particularly effective in phenolic acid extraction, with a recovery yield gradually increasing with residence time and temperature [309]. The increase of ferulic and diferulic acids release from destarched bran has been in particular associated to the degradation and depolymerisation of the hemicellulosic arabinoxylans, along with some breakdown of cellulosic glucose [310]. Thermal pretreatment is often adopted because of the simplicity of the required equipment and the absence of corrosive and hard to recycle chemicals [311].…”

Bacterial Xylanase in Pseudomonas boreopolis LUQ1 is Highly Induced by Xylose

“…There are at least two main reasons for this. One is that wheat bran has lower lignin content and 18% protein, thus serving both as a carbon and a nitrogen source [17]. The other reason is that wheat bran is easily degraded and releases low mass saccharides to induce the microorganism to produce more xylanase.…”