Development of Hyperspectral Imaging Technique for the Detection of Chilling Injury in Cucumbers; Spectral and Image Analysis

Hyperspectral images of cucumbers were acquired before and during cold storage treatment as well as during subsequent room temperature (RT) storage to explore the potential for the detection of chilling induced damage in whole cucumbers. Region of interest (ROI) spectral features of chilling injured areas, resulting from cold storage treatments at 0 C or 5 C, showed a reduction in reflectance intensity during multi-day post-chilling periods of RT storage. Large spectral differences between good-smooth skins and chilling injured skins occurred in the 700to 850-nm visible/NIR region. A number of data processing methods, including simple spectral band algorithms and principal component analysis (PCA), were attempted to discriminate the ROI spectra of good cucumber skins from those of chilling injured skins. Results revealed that using either a dual-band ratio algorithm (Q811/756) or a PCA model from a narrow spectral region of 733to 848-nm could detect chilling injured skins with a success rate of over 90%. Furthermore, the dual-band algorithm was applied to the analysis of images of cucumbers at different conditions, and the resultant images showed more correct identification of chilling injured spots than PCA method. The results also suggested that chilling injury was relatively difficult to detect at the stage of the first 0 to 2 days of post-chilling RT storage, due to insignificant manifestation of chilling induced symptoms.