Structural features of cell-wall polymers of the apple

Abstract

Cell-wall material was isolated from ripe-apple cortical tissues by sequential extraction with aqueous 1.5% sodium dodecyl sulphate and aqueous 90% methyl sulphoxide. The wall material, which contained ∼1% of protein, with proline and hydroxyproline as the preponderant amino acids, was sequentially extracted with water at 80°, oxalate at 80°, m KOH at 1°, and m and 4 m KOH at 20°, to leave a residue of α-cellulose, which was associated with an appreciable amount of arabinose-rich pectic material. The depectinated material was also extracted with 6 m guanidinium thiocyanate at 20° to solubilise preferentially polysaccharides rich in mannose. The hot-water-soluble pectic substances were richer in arabinose compared with the oxalate-soluble ones and were resolved into five fractions by anion-exchange chromatography. The bulk of the hemicelluloses, which were xyloglucans, were solubilised by 4 m KOH. The alkali-soluble hemicellulose polymers were resolved by anion-exchange chromatography into polysaccharides, mainly xyloglucans, arabinoxylan-pectic-xyloglucan, and arabinoxylan-pectic complexes. Small amounts of polysaccharide-protein-polyphenol complexes (where the polysaccharide moieties were arabinoxylans), pectic substances, and xyloglucans were also present. The glycosidic linkages of the above polymers were determined by methylation analysis. The general structural features of the cell-wall polymers are discussed.