Does total antioxidant capacity play a central role in postharvest deterioration of ‘Sweetheart’ sweet cherry fruit?

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'Sweetheart' cherries (Prunus avium L.) have sweet flavour, bright red colour and a distinctive heart shape which contributes to their wide commercial acceptance. They display also comparatively high firmness and long shelf-life potential. Enzyme-catalysed disassembly of cell walls has been generally targeted as the main factor accounting for ripening-related changes in fruit firmness and overall texture, but the biochemical mechanisms involved in this process appear to include additional factors such as oxidative scission of cell wall polysaccharides. In this study, 'Sweetheart' fruit were hand-collected at commercial maturity, and kept at 0 oC for 15 or 30 days plus 3 days at 20 oC to mimic their retail period. Firmness, weight loss and juiciness, together with the incidence of decay and stem browning, were chosen as indicators of commercial quality of fruit. Cell wall materials were extracted and fractionated, related enzyme activities were assessed, and ascorbic acid content as well as radical scavenging activity (RSA) were also determined. Fruit displaying higher RSA showed higher values for firmness and lower weight loss, decay and stem browning incidence. Higher firmness levels were associated to higher RSA and to yields of the cell wall fractions enriched in convalently-bound pectins and hemicelluloses. β-galactosidase, pectinmethylesterase and endo-1,4-β-D-glucanase activities correlated inversely to firmness, while pectate lyase activity appeared to be relevant for solubilisation of cell wall materials and was inversely related to ascorbic acid content.