Optical Properties of Fruits and Vegetables to Serve the Automatic Selection within the Packing House Line (4)

Delayed Light Emission as a Means of Automatic Selection of Tomatos

Abstract

The factors which affect the intensity of delayed light emission (DLE) of tomato were investigated for the purpose of developing an automatic sorting mechanics, and the following results were obtained;
1. The relation between dark period and DLE intensity was investigated (Fig. 2). General working conditions, based on this result, were established as
Dark period for dark recovery of DLE; above 10 minutes, Decay period; above 0.7 seconds.
2. DLE intensity of tomato was saturated by the excitation of 5500lx for 3 to 6 seconds having the dark period of 10 minutes (Fig. 3).
3. Exciting illuminance needed for the DLE saturation of tomato increased inversely with the decrease of decay period. For the decay period of 1 second the illuminance for the saturation was 2750lx (Fig. 4).
4. The DLE intensity was directly proportional to the excitation area on tomato (Fig. 5).
5. Maximum DLE intensity of tomato was obtained at the flesh temperature of 13 to 17°C (Fig. 6)
6. The relation between the chlorophyll content and the DLE intensity was almost linear (Fig. 7).
7. Color sorting accuracy of tomato was investigated by means of DLE (Table. 2). The green tomatoes were sorted with high accuracy whereas that of the red tomatoes did not follow.
Separation of green tomato from breaker is of much importance from the point of practical application (breaker has a small white or pink star at the blossom end and may be ripened several days later).
8. The relation between the thickness of tomato flesh and the DLE intensity was investigated. Green ripe tomato emitted high delayed light from the flesh of 6mm thick, which was the same level with that of a whole or a half tomato. In case of red ripe tomato which contained a little amount of chlorophyll, a trace of DLE was observed which was not supposed to be influential on sorting accuracy (Fig. 8).
9. The DLE spectrum of intact tomato had a peak at the wavelength of 695nm and a bulge on the longer side, and agreed well with the fluorescence spectrum of chlorophyll.
Photomultiplier having a high sensitivity around the wavelength of 695nm is recommended as a DLE detector.