Near-infrared Spectroscopy and Aquaphotomics on Chilling Injured Kiwifruit

For most fruits, cool-storage is the primary means by which quality is maintained after harvest. However, prolonged long storage at low temperature can cause the breakdown of tissues, known, for kiwifruit, as low-temperature breakdown or chilling injury (CI). The resulting damage reduces the fruit quality and shelf life, leading to financial losses. Symptoms of kiwifruit CI include granular or corky tissue in the outer pericarp, water-soaked areas in the outer and inner pericarp, and, in advanced stages, external skin discoloration. Currently, the presence of CI in kiwifruit can be detected visually only when the fruit is cut open. A non-destructive method of detecting kiwifruit CI would be beneficial. Near-infrared spectroscopy (NIRS) is a popular and efficient non-destructive method for internal quality evaluation of fruits and vegetables, including aspects such as soluble solids content (SSC), dry matter. A typical NIRS set-up uses a broadband light source to illuminate the sample, and the reflected or transmitted light is measured using a spectrometer. As the water absorption peaks at 1450 and 970 nm in the kiwifruit change with temperature and SSC, the differences between control and CI kiwifruit can be traced by observing changes in the water spectral patterns presented on an aquagram. We investigated aquaphotomics to identify changes in the water structure caused by CI in Actinidia chinensis var. chinensis 'Zesy002' kiwifruit. Water bands were identified for CI kiwifruit juice in the first overtone region and whole intact fruit in the second overtone region of the OH stretch of water. For both juice and intact fruit measurements, CI increased hydrogen-bonded water species. This finding can help in the development of a portable sensor for CI measurement of intact fruit since most of the information about the CI of fruit resides in the region of water bands.