Non-destructive Measurement of Chlorophyll Concentration of Fruit Skin in Japanese Pear

In order to develop a non-destructive method to measure the chlorophyll concentration of fruit skin in Japanese pear (Pyrus pyrifolia), reflectance of diffused light through the skin of fruit over a cork layer was measured using a portable spectrometer. Reflectance was acquired in the 650–740 nm wavelength range to establish a model to predict chlorophyll a and b concentrations using partial least squares regression. The chlorophyll concentration was precisely predicted by each model (r 2 = 0.962–0.974) in ‘Kosui’, ‘Hosui’, and ‘Akizuki’ in 2016. Chlorophyll concentrations of these three cultivars in 2016 were also estimated with small errors using the prediction model of ‘Kosui’ in 2017. The chlorophyll concentration showed a high correlation with the ground color index (r 2 = 0.937–0.953) in all cultivars. The prediction model was affected by the temperature of fruit. However, the error decreased with the prediction model established based on mixed fruit with various temperatures. The chlorophyll concentration measured in the field exposed to sunshine showed almost the same value as that measured under room conditions. From these results, the chlorophyll concentration could be non-destructively, precisely, and rapidly estimated over a cork layer either in a room or field using the portable spectrometer, and this can be used to confirm the maturity of Japanese pear.