A system using in situ NIRS sensors for the detection of product failing to meet quality standards and the prediction of optimal postharvest shelf-life in the case of oranges kept in cold storage

The viability of using near infrared (NIR) spectroscopy was studied as a non-destructive analytical technique with the potential of being applied in situ to establish quality standards and the postharvest shelf-life of oranges kept in cold storage, as well as to detect substandard produce. In specific terms, it was applied to assessing the viability of increasing the period of postharvest storage depending on the quality exhibited by the produce. Initially, the spectral information from 80 oranges stored for up to four weeks in refrigeration chambers was used, this being the maximum postharvest storage time in the citrus industry in the south of Spain, to establish the natural variability in spectra from refrigerated oranges meeting quality standards. The processing of the spectral data was carried out using principal component analysis and the spectral distances between the sets (fruit belonging to weeks 1 to 4 of cold storage) were calculated using n-dimensional statistics such as the Mahalanobis distance. Subsequently, oranges stored for between five and ten weeks were spectrally analysed and their distances from the standard or control population, described above, were calculated. The results were represented in the form of a Shewhart control chart, in which the mean scores and the corresponding control limits serving as warning systems were established. The findings suggest that NIR spectroscopy and the use of spectral distances will enable an innovative quality control system to be developed, based on spectral information that allows the establishment of quality standards in oranges, and the detection of non-standard produce.