Postharvest ripening-induced modification of cell wall polysaccharide affects plum phenolic bioavailability

The mechanisms by which cell wall polysaccharides regulate phenolic release are essential to human health. Scanning electron microscopy (SEM), surface area and porosimetry analyzer, high-performance liquid chromatography (HPLC), and atomic force microscopy (AFM) indicated that compared to fresh plums, postharvest ripening reduced chain linearity in the homogalacturonan region of pectins and the degree of branching of RG-I; pectin and hemicellulose underwent solubilization and depolymerization by cell wall-degrading enzymes; and the specific surface area of cellulose was reduced by 19.5 %-26.8 %, with aggregation of cellulose occurring. In addition, confocal laser scanning microscopy (CLSM), polyphenol adsorption experiments, and in vitro gastrointestinal digestion experiments showed that the cell wall modifications under postharvest ripening process induced phenolics release and increased the bioaccessibility of plums: compared to the fresh plums, the equilibrium adsorption capacity of the cell wall of late postharvest ripened plums was reduced by 42.6 % (for epicatechin) and 27.4 % (for chlorogenic acid), and the bioaccessibility index of postharvest plum phenolics was increased by 11.2 %-23.9 %. These findings indicate cell wall modification under postharvest ripening process induces phenolic release and improves plum phenolic bioavailability.