Optical Properties of Fruits to serve the Automatic Selection in the Packinghouse line (2)

Light Reflectance of Satsuma Orange

Abstract

Grading of citrus fruits was done by manual sorting based on the external appearance and color. Due to this manual labor within the grading line of citrus, it became quite impossible to increase the sorting rate of fruits together with sortillg efficiency.
From this point of view, it becomes meaningful that an automatic color sorting facility should be planned and manufactured.
Optical reflectance properties of Satsuma Orange, Citrus Unshiu Marc., were investigated to serve the automatic grading in the packing house line.
The results obtained were as follows:
1. Reflectance for distinguishing the degree of peel color should be best measured at near the wavelength of 680nm.
2. The color grade or HUE of Satsuma Orange was found to be directly proportional to the logarithm of chlorophyll content.
Reflectance out put or criterion I₁ due to the measuring wavelength at 680nm was proportional to log (chl.)≡X,
I₁=-0.33X+0.29(-1.4≤X≤0.9)
3. The criterion I₁ was also found to be proportional to the illuminated area on the glass sphere filled with milk solution.
I₁=0.023A(A≤30cm²)
4. To eliminate the effect of size variation and apparatus sensitivity, measurements of reflectance were made in regard to couple of wavelength.
One wavelength must be sensitive to chlorophyll content, another must be insensitive to it. This new color criterion I₂ was expressed as
I₂(λ₁λ₂)=C(λ₁)R(λ₁)A/C(λ₂)R(λ₂A)=KR(λ₁)/R(λ₂)
The measuring and reference wavelengths of one possible conbination was 680nm and 740nm, respectively.
The regression equation is:
I₂=-0.43X+0.38, r=0.97
5. The effect of peel treatments, in the packing house line, on the value of criterion I₂ was almost negligible.
6. Graphical representation of correlation coefficients of the possible combinations of reflectance intensity ratio (I₂) with the chlorophyll content as in fig. (8), is shown in fig. (10).