Chemical and structural characterization of hemicellulose from date fruits (Phoenix dactylifera L.)

In this study, we extracted hemicellulose from two date fruit cultivars (soft Barhi and hard Neghal) and investigated their structural, physicochemical, and thermal properties. Alkali solubilized more hemicellulose (45%-47.5%) than DMSO (6%-7%); however, DMSO preserved the feruloyl ester linkages. The monosaccharides constituent of hemicellulose includes xylose (33.1-70.6%), glucose (6.7%-17.2%) uronic acids (5.5%-13.3%), arabinose (3.2%-10.1%), galactose content (4.8%-6.8%), mannose (1.6%-3.6%), and rhamnose (0%-3.1%). The hemicellulose was primarily β-(1 → 4)-linked arabinoxylans with minor glucurono-/galacto-arabinoxylan motifs, together with insoluble glucan and pectic homogalacturonan (HG) and rhamnogalacturonan-I (RG-I). Neghal hemicellulose was structurally simpler, containing relatively less branched arabinoxylan and showing lower peak-molecular weights (27.5-35 kDa), whereas Barhi hemicellulose was enriched in arabinogalactan-protein (AGP) and RG-like features and showed higher peak-molecular weights (29.5-223.9 kDa). These structural differences correlate with a more branched, hydrated and less tightly packed hemicellulose-pectin matrix in Barhi compared with a more dominated arabinoxylan-matrix in Neghal and may contribute to the softer texture of Barhi. Overall, these results provide new insights into the composition and structural diversity of alkali-soluble hemicellulosic polysaccharides in date fruits.