Abstract
To investigate the physiological and molecular properties relating to cell wall carbohydrate metabolism in fruit, the ultrastructure and polysaccharides compositions of the cell wall, as well as the fruit quality and activities of enzymes relating to fruit softening, were studied for three Hami melon varieties (‘Xizhoumi 17’, ‘Jinhuami 25’, and ‘Chougua’) representing three different storability levels. The results showed that ‘Chougua’ maintained a higher firmness on day 18, with the lowest decay incidence (0%). ‘Chougua’ showed a better storage quality and intact cell wall structure. The molecular weight and monosaccharide composition of cell wall polysaccharides for Hami melons underwent great changes during storage, and the degradation of pectin polysaccharides was obvious, involving the depolymerization of macromolecular polymers accompanied by the production of new macromolecular polymers and composition changes in pectin monosaccharides (glucose, galactose, and arabinose) during the softening process of the Hami melons. Polygalacturonase, pectin methylesterase, xyloglucan endo-transglycosylase/hydrolase, α-arabinofuranosidase, β-galactosidase, and cellulase were associated with fruit softening at different stages of storage. There were similar softening mechanisms in the three Hami melons. This study will provide reference for further study on the fruit softening mechanisms of Hami melons.
Highlights
Fruit softening during postharvest storage is closely related to changes in cell wall structure and composition, and it tends to have great negative influences on fruit appearance, texture, flavor, and aroma [1]
The results indicated that Cell wall material (CWM), water-soluble fraction (WSF), and CF had a great impact on fruit softening
The softening mechanisms of the three landraces were similar from the perspectives of molecular weight and monosaccharide composition in different pectin polysaccharides and cell wall metabolic enzymes
Summary
Fruit softening during postharvest storage is closely related to changes in cell wall structure and composition, and it tends to have great negative influences on fruit appearance, texture, flavor, and aroma [1]. Wei et al (2015) and Chea et al (2019) found that the hemicellulose, pectin, and cellulose in cell wall have obvious changes during fruit ripening, and the synergistic action of cell-wall-modifying enzymes, mainly including polygalacturonase (PG), β-galactosidase (β-GAL), α-arabinofuranosidase (α-ARF), pectin methylesterase (PME), xyloglucan endo-transglycosylase/hydrolase (XTH), and cellulase (Cx), are involved in the process. Hami melon (Cucumis melo L.) is a climacteric fruit which ripens and undergoes senescence rapidly after harvest, with has serious decay loss. It has been favoured by customers for years because of its sweet flesh and abundant nutrition [5]. Few reports explore the internal relationships among cell wall composition, cell-wall-modifying enzymes, and fruit softening of Hami melon
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