Abstract
BackgroundIn view of the natural resistance of hemicelluloses in lignocellulosic biomass on bioconversion of cellulose into fermentable sugars, alkali extraction is considered as an effective method for gradually fractionating hemicelluloses and increasing the bioconversion efficiency of cellulose. In the present study, sequential alkaline extractions were performed on the delignified ryegrass material to achieve high bioconversion efficiency of cellulose and comprehensively investigated the structural features of hemicellulosic fractions for further applications.ResultsSequential alkaline extractions removed hemicelluloses from cellulose-rich substrates and degraded part of amorphous cellulose, reducing yields of cellulose-rich substrates from 73.0 to 27.7% and increasing crystallinity indexes from 31.7 to 41.0%. Alkaline extraction enhanced bioconversion of cellulose by removal of hemicelluloses and swelling of cellulose, increasing of enzymatic hydrolysis from 72.3 to 95.3%. In addition, alkaline extraction gradually fractionated hemicelluloses into six fractions, containing arabinoxylans as the main polysaccharides and part of β-glucans. Simultaneously, increasing of alkaline concentration degraded hemicellulosic polysaccharides, which resulted in a decreasing their molecular weights from 67,510 to 50,720 g/mol.ConclusionsThe present study demonstrated that the sequential alkaline extraction conditions had significant effects on the enzymatic hydrolysis efficiency of cellulose and the investigation of the physicochemical properties of hemicellulose. Overall, the investigation the enzymatic hydrolysis efficiency of cellulose-rich substrates and the structural features of hemicelluloses from ryegrass will provide useful information for the efficient utilization of cellulose and hemicelluloses in biorefineries.
Highlights
In view of the natural resistance of hemicelluloses in lignocellulosic biomass on bioconversion of cellulose into fermentable sugars, alkali extraction is considered as an effective method for gradually fractionating hemicelluloses and increasing the bioconversion efficiency of cellulose
The hemicelluloses in the plant cell wall have an inhibitory effect on the enzymatic hydrolysis of cellulose, since this component covers the cellulose microfibers and further forms a physical barrier to prevent the entry of enzymes [8]
This result was consistent with the chemical compositions of hemicellulosic fractions obtained from sequential alkaline extractions
Summary
In view of the natural resistance of hemicelluloses in lignocellulosic biomass on bioconversion of cellulose into fermentable sugars, alkali extraction is considered as an effective method for gradually fractionating hemicelluloses and increasing the bioconversion efficiency of cellulose. Pretreatment of lignocelluloses is the process which removes hemicelluloses and lignin, reduces cellulose crystallinity, and increases accessibility of material for enzymes [6, 7]. Hydrogen and covalent bonds (such as ester and ether bonds) are broken, resulting in alteration of lignin structure and disruption of crosslinks between hemicelluloses and other components [12]. The cleavage of these linkages facilitates dissociation of entire cell wall of lignocelluloses and solubilization of hemicelluloses and lignin, improving accessibility of lignocellulose. Hemicelluloses can be recovered by alkaline treatment for further utilization
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