Structural elucidation of hemicelluloses from oil-tea camellia fruit shell

Abstract

Oil-tea camellia fruit shell (CFS) is a very abundant waste lignocellulosic resource. The current treatments of CFS, i.e. composting and burning, pose a severe threat on environment. Up to 50 % of the dry mass of CFS is composed of hemicelluloses. However, chemical structures of the hemicelluloses in CFS have not been extensively studied, which limits their high-value utilization. In this study, different types of hemicelluloses were isolated from CFS through alkali fractionation with the assistance of Ba(OH)₂ and H₃BO₃. Xylan, galacto-glucomannan and xyloglucan were found to be the major hemicelluloses in CFS. Through methylation, HSQC and HMBC analyses, we have found that the xylan in CFS is composed of →4)-β-D-Xylp-(1→ and →3,4)-β-D-Xylp-(1→ linked by (1→4)-β glycosidic bond as the main chain; the side chains are α-L-Fucp-(1→, →5)-α-L-Araf-(1→, β-D-Xylp-(1→, α-L-Rhap-(1→ and 4-O-Me-α-D-GlcpA-(1→, connected to the main chain through (1→3) glycosidic bond. The main chain of galacto-glucomannan in CFS consists of →6)-β-D-Glcp-(1→, →4)-β-D-Glcp-(1→, →4,6)-β-D-Glcp-(1→ and →4)-β-D-Manp-(1→; the side chains are β-D-Glcp-(1→, →2)-β-D-Galp-(1→, β-D-Manp-(1→ and →6)-β-D-Galp-(1→ connected to the main chain through (1→6) glycosidic bonds. Moreover, galactose residues are connected by α-L-Fucp-(1→. The main chain of xyloglucan is composed of →4)-β-D-Glcp-(1→, →4,6)-β-D-Glcp-(1→ and →6)-β-D-Glcp-(1→; the side groups, i.e. β-D-Xylp-(1→ and →4)-β-D-Xylp-(1→, are connected to the main chain by (1→6) glycosidic bond; →2)-β-D-Galp-(1→ and α-L-Fucp-(1→ can also connect to →4)-β-D-Xylp-(1→ forming di- or trisaccharide side chains.

Keywords: Glucomannan; Glycosidic bond; Xylan; Xyloglucan.