[The Effects of Skin Thickness on Optical Transmission Characteristics in Fruits Tissues]

Fruit quality inspection techniques play a very important role in the production and consumption of fruits. In the field of quality non-destructive inspection and grading for fruits, the light-based techniques using optical properties of fruit products were widely used as one of the most practical and the most successful techniques. Quantitative understanding of light interaction with fruits is critical to designing better optical systems for inspection of food quality. In this paper, a fruit model consisted of two layer tissues was developed using Monte Carlo simulations to explore the light transport process and properties in the pome fruits, such as apples and mandarins, which were used as the thin-skinned and thick-skinned fruits respectively. The simulation results obtained are based on the assumption that the light source is a Gaussian beam at the wavelength 808 nm. This paper reports that the effects of skin thickness on light transmission characteristics in fruit tissues, including diffuse reflectance, transmittance, absorptivity, penetration depth etc. The inspection efficiency of flesh tissues was also demonstrated. The results indicated that the transmittance and the penetration depth decreases with the fruit skin increasing. As for the absorbed energy density, the fruit skin tissues have the wider distribution at the radial distance than the fruit flesh tissues. The absorbed energy density always tended to decrease with the inside depth of the fruit tissues increasing, especially decreased more apparently at the radial direction. The diffuse reflectance at the radial distance from 0.2 to 1.2 cm decreased with the decreasing of fruit skin, however it showed the inverse relationship in the radial distance range from 1.2 to 4.0 cm, the diffuse reflectance decreases with the increasing fruit skin. This paper proposed that the interaction between light and fruits skin in transmission or reflective approach, should be considered for developing optical techniques of non-destructive fruit quality inspection. And it provided a theoretical basis for designing more efficient optical detection device, including how to confirm the light source power, size and position of the detector, etc. It has very important significance for fruit quality inspection by optical techniques.