Prediction of the optimum harvest time of 'Scarlet' apples using DR-UV-Vis and NIR spectroscopy

The identification of the harvest date plays a key role in the agro-food chain as the quality of fruit basically depends on the right harvesting time and appropriate storage conditions during the post-harvest period. Destructive techniques, like some ripening parameters, suffer from several drawbacks that highlight the market need for reliable non-destructive tools to determine ripeness level. This work is focused on the study of ripening of red apples (Scarlet cv), with the aim of better identifying the harvest date, by means of non-destructive analysis, through the characterization of each fruit ripening stage on the trees, and classical methods, using as a reference. UV-Vis analysis was applied in diffuse reflectance (DR) mode to monitor the variations in the chlorophyll content of the skin of red apples during the ripening phase on the trees, since the colour variation in red apples is difficult to observe during ripening, and the ground colour cannot be considered a valid tool to identify ripening. On the other hand, the variation in the chlorophyll content, measured by means of in-situ DR-UV-Vis spectroscopy, is as an reliable indicator of the ripeness stage. The novelty of this work concerns the fact that a backward interval-GA-Partial Least Squares (PLS) model, based both on NIR and UV-Vis data, has been used to predict the optimal harvesting time in a direct way, and to obtain a complete overview of fruit maturation through the comparison with UV-Vis analysis and the calibrations of the ripening parameters.