Internal and external quality assessment of mandarins on-tree and at harvest using a portable NIR spectrophotometer

Abstract

Citrus growers are increasingly demanding rapid, cost-effective, green, and non-destructive methods for monitoring changes in physical–chemical quality during on-tree ripening, with a view to establishing the optimum harvest date. This study sought to evaluate the performance of a handheld MEMS-based NIR spectrophotometer, used in conjunction with chemometric techniques, for the prediction of changes not only in major external quality parameters such as weight, size (equatorial and axial diameters) and color (L*, a*, b*, C*, h*, color index), but also in internal physical parameters (firmness, maximum penetration force, pericarp thickness, juice weight, juice content) and chemical properties (soluble solids content, pH, titratable acidity, maturity index) in intact mandarins during the pre-harvest period, as a means of establishing the most suitable harvest date. The models obtained by applying MPLS regression to spectroscopic data yielded promising results for on-tree external quality measurements, particularly for color-related parameters (a*, C* and color index), and for all the internal chemical parameters studied. These results confirm that changes in intact mandarin quality parameters during on-tree ripening can be measured non-invasively using the new generation of portable MEMS-based NIRS sensors, allowing the ripening process to be charted in individual fruits not only in terms of visual appearance, but also in terms of taste- and texture-related features, this being a major step towards the selective harvesting of citrus fruits depending on their final destination.