Delayed Luminescence in Monitoring the Postharvest Ripening of Tomato Fruit and Classifying According to Their Maturity Stage at Harvest

Ripening is an irreversible phenomenon involving several physiological, biochemical and organoleptic changes that affect the nutritional value, colour, texture and taste of fruit. Amongst the physical non-destructive technologies, Delayed Luminescence (DL) has been reported able to provide valid information on the functional status of living biological systems, reflecting changes in quality parameters following the occurrence of certain metabolic processes. In this study, we followed up and analysed the variations in the colour and DL signals emitted by tomato fruit as a function of their ripening degree. Four lots of tomato fruit, similar to each other for cultivar and geographical origin, were considered. Tomatoes were harvested at various maturity stages and stored in the dark at room temperature. The changes in DL emission trends were monitored at different times after harvesting for a period of about 20 days and correlated with the a*/b* colour ratio, which is normally used as an indicator of fruit ripeness degree. Results highlighted that the emission intensities, as well as the parameters by fitting DL decay curves, were strongly dependent on harvest maturity, varying significantly even as fruit ripeness progressed after their harvesting. Significant differences were also found between DL signals emitted by field-ripened tomatoes at the beginning of storage and those emitted by postharvest-ripened tomatoes at the end of the storage period. Delayed Luminescence may be used as a fast, reliable and sensitive tool for evaluating, more generally, the sensorial quality of fruit during postharvest storage.