Knowledge of the optical properties of apple tissues such as skin and flesh is essential to better understand the light-tissue interaction process and to apply optical methods for apple quality inspection. This work aimed at estimating the anisotropy factor of thin skin and flesh samples extracted from three apple cultivars. The scattering-angular light distribution in each tissue sample was measured at four wavelengths (λ=633, 763, 784, and 852 nm), by means of a goniometer setup. Based on the recorded angular intensity I(θ,λ), the effective anisotropy factor g_eff of each tissue type was first estimated using the mean statistics applied to the random variable cos θ. Next, the measured data were fitted with three predefined and modified phase functions-Henyey-Greenstein (p_MHG), Gegenbauer kernel (p_MGK), and Mie (p_Mie)-in order to retrieve the corresponding anisotropy factors g_MHG, g_MGK, and g_MMie. Typically, the anisotropy factors of skin and flesh amount to 0.6-0.8 in the above-mentioned wavelength range.

This paper reports on the quantification of light transport in apple models using Monte Carlo simulations. To this end, apple was modeled as a two-layer spherical model including skin and flesh bulk tissues. The optical properties of both tissue types used to generate Monte Carlo data were collected from the literature, and selected to cover a range of values related to three apple varieties. Two different imaging-tissue setups were simulated in order to show the role of the skin on steady-state backscattering images, spatially-resolved reflectance profiles, and assessment of flesh optical properties using an inverse nonlinear least squares fitting algorithm. Simulation results suggest that apple skin cannot be ignored when a Visible/Near-Infrared (Vis/NIR) steady-state imaging setup is used for investigating quality attributes of apples. They also help to improve optical inspection techniques in the horticultural products.