Abstract
This work aimed to (i) determine the reliability of a portable Bluetooth colourimeter for fruit colour measurements; (ii) characterise the changes in quantitative skin colour attributes in a nectarine cultivar in response to time from harvest; and (iii) determine the influence of row orientation and training system on nectarine skin colour. The skin colour attributes measured with the colourimeter, namely L*, a* and b*, were calibrated and validated against a reference spectrophotometer. C* and h° were obtained from a* and b*. Skin colour was measured in situ from 42 days before to 6 days after harvest on ‘Majestic Pearl’ nectarines subjected to different row orientations and training systems. Validation models showed high reliability of colour estimations. The trends of colour attributes over time were characterised by cubic regression models, with h° proving to be the best parameter to describe changes of colour over time, with a clear link to the maturation process. No significant effects of row orientation and training system on skin colour were observed at harvest. Overall, the device proved reliable for fruit colour detection. Results of this study highlight the potential of h° as a quantitative index to monitor ripening prior to harvest in ‘Majestic Pearl’ nectarines.
Highlights
The quadratic models had R > 0.9 (Table 1) and were used to calibrate the L*, a* and b* measurements obtained with the colourimeter from the uncalibrated readings (i.e., L*u, a*u and b*u)
The handheld Bluetooth colourimeter used in this study proved accurate and precise for the detection of L*, a* and b* in stone fruit, as demonstrated by the cross-validation results shown in Figure 4 and Table 2 on a comprehensive dataset that included different stone fruit crops
The instrument allows for very rapid measurements and can be used for data collection in situ or post-harvest as it is interfaced via Bluetooth connectivity with a smartphone application that serves as data logger and stores data in the internal memory
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Fruit quality represents an important driver for future increases in value for exported Australian stone fruit. Stone fruit quality is not well defined, and it is strongly affected by the preferences of consumers, who generally demand red fruit with high sugar content. Fruit colour is one of the quality parameters that tends to be stable among different markets
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