Evaluation of Surface Color of Japanese Persimmon Fruits by Light Reflectance

Abstract

In order to improve and mechanize the grading system of Japanese persimmon fruits, which was now relying on manual human sorting, the spectral reflectance of persimmons was measured.
The fundamental data were obtained as follows;
1. For the diameter of 20mm of sample port, the spectral reflectance intensity was not affected by the size of samples.
2. The largest change of the attenuance, i. e. log (1/R), occured at the absorption band of chlorophyll of 680nm.
The attenuance (E_r) at 680nm had a linear regression with the chlorophyll content (Chl.) of persimmons, and the correlation was significant at 1% level. Chl.=0.00652×E_r+0.00246
r=0.73
Therefore, the surface color of the persimmons could be evaluated by measuring the spectral reflectance at the wavelength of 680nm.
3. The spectral reflectance of the persimmons was affected by the peel and flesh of the thickness of 4-5mm below the surface. Furthermore, the attenuance increased rapidly as the thickness of peel and flesh decreased. These indicated that the spectral reflectance mainly depended on the body reflection of the peel and flesh within the thickness of 4mm.
4. The attenuance changed due to the orientation of the cheek of a persimmon. The difference of surface color on the location of a fruit was found not to be negligible. The spectral reflectance should be measured from various orientations of a fruit for the correct evaluation of surface color.
5. With the lapse of time after picking, the attenuance of unripe persimmons decreased near the wavelength of 680nm, but the attenuance of overripe ones increased at the whole wavelength from 550nm to 750nm. The additional measurement was required when the overripe persimmons were graded out from the unripe and the ripe ones because the attenuance showed the different change between the stages before and after full ripening.