Effects of ripening stage and cultivar on physicochemical properties and pectin nanostructures of jujubes

Two Chinese jujube (Zizyphus jujuba) cultivars (‘Huanghua’ and ‘Zhanhua’) at unripe and ripe stages were investigated. During ripening, the weight, pH, hardness, and chewiness of both cultivars decreased while titratable acidity, total soluble solid content, and pectin contents increased. More than 75% pectins of the fruits were water-soluble pectin (WSP). Pectins shared the common major compositions of Gal, Rha and GalUA. For both cultivars, most of the chain widths were between 47 and 70 nm for unripe while less than 40 nm for ripe jujubes. Compared to unripe fruits, all pectins of ripe fruits had less percentage of wide and long pectin chains. All the pectin contents of cultivar ‘Huanghua’ changed to a degree greater than that of cultivar ‘Zhanhua’ during ripening. Changes of pectin nanostructure and neutral sugar composition might be responsible for the major physicochemical properties of jujubes.