Occurrence of early softening in papaya due to specific cell wall-related changes

This study aims to find characteristics that might explain the rapid softening disorder in papaya. At the time of harvest, it was observed that papaya with early softening disorder (ESD) and those without the disorder could not be distinguished exclusively on the basis of their skin color and pulp firmness. Fruit with ESD and without ESD were harvested at maturity stage 1 and evaluated for 10 d at 10 °C, according to the softening index (SI) methodology. The symptoms of early softening disorder were clearly observed between 2 d and 8 d of storage, with firmness 71% lower than the initial firmness, presenting atypical behavior for fruit stored under refrigeration. There was no difference between the fruit with and without ESD for soluble solids contents, but titratable acidity and ascorbic acid were significantly different between both stages of fruit that could be associated with the ripening patterns. Furthermore, there were no differences between fruit with ESD and those without ESD in respiratory rate and ethylene production under refrigerated storage, what suggested that the occurrence of disorder was not related to an increase in ethylene post-harvest period. This work provided evidence to discriminate fruit susceptible to suffer from ESD from those not susceptible to this disorder. The cell wall polysaccharide fractions indicated significant differences between fruit with ESD and without ESD at the moment of harvest suggesting modifications in the cellulose-hemicellulose domain. Moreover, the ethylene production did not follow cell wall modification, suggesting that changes in the cell wall structure could have happened during fruit growth. In this way, depending on the intensity of the cell wall modification, the fruit will exhibit the flesh early softening after harvest.