Epidermal wax damage on Hami melon (Cucumis melo L.) caused by postharvest commercialization induced fruit physiological softening and degradation of pectin polysaccharide nanostructure

Abstract

Postharvest commercial-induced epidermal wax damage (EWD) caused rapid softening in Hami melon, impacting market value. EWD on the physicochemical and texture peculiarity, ultrastructure, cell wall materials (pectin, hemicellulose, and cellulose), molecular weight (Mw) and nanostructure of pectin in Hami melon (‘Jinhuami 25’, ‘Xizhoumi 17’ and ‘Chougua’) were explored. EWD resulted in physicochemical changes, including decreased SSC/TA and textural properties, increased weight loss and water-soluble pectin, and alterations in cell wall regulating enzymes. Enlargement of intercellular space was observed in EWD group by TEM. Mw demonstrated the depolymerization and degradation of pectin. AFM analysis indicated EWD induces the depolymerization of pectin polysaccharide main and side chains at nanoscale, characterized with higher frequency of shorter chain length and narrower chain widths in pectic molecules versus CK group. The extended shelf-life of ‘Chougua’ in EWD group attributed to the maintenance of cell wall integrity, coupled with high polymerization state and branching degree of pectin molecules. Fundamental width units of Hami melon pectin chains were measured at 11.7, 15.6, 17.6, 19.5, and 29.3 nm. The study introduces the molecular chain width degradation model of Hami melon pectin, shedding light on the quality evolution and the mechanism of softening in Hami melon induced by EWD.