Nondestructive Apple Ripening Stage Determination Using the Delta Absorbance Meter at Harvest and after Storage

The delta absorbance (DA) meter is a handheld instrument which noninvasively measures the chlorophyll content in fruits. In the present work, it was used to monitor the ripening process linked to the climacteric phase in apple (Malus×domestica). The results [index of absorbance difference (IAD)] were correlated to quality attributes at harvest and after commercial scale storage at different conditions. Two cultivars (Red Delicious, Golden Delicious) were analyzed in two different seasons, whereas Morgenduft and Gala were analyzed only in the first and second seasons, respectively. In general, a linear reduction of the IAD values was observed in all apple cultivars along with the progression of ripening and ethylene biosynthesis. When ethylene production was inhibited by 1-methylcyclopropene (1-MCP) treatment, the decrease of IAD values was markedly reduced. IAD threshold values for each cultivar were identified, delineating the central phase of the ethylene climacteric rise. Predictive models were built by correlating IAD index to the soluble solids concentration (SSC), titratable acidity (TA), and firmness measured at harvest and after removal from different storage regimes. The best model was developed for SSC prediction on ‘Red Delicious’ apple [ratio performance deviation (RPD) = 1.88] and for firmess evaluation in ‘Golden Delicious’ apple (RPD = 1.84). Moreover, IAD values were consistently associated with the differences in fruit quality as affected by optimal and suboptimal storage conditions. The IAD, due to its acceptable accuracy and speed of assessment, can be a promising tool for assisting in sorting apples before and after storage in warehouses or commercial packing lines. IAD cannot totally replace standard ripening indices, but can effectively supplement data for these parameters.