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Insight in the transmission of light through intact fruit is important to optimize and interpret the signals acquired with spectroscopy methods such as tunable diode laser absorption spectroscopy (TDLAS). To this end, we quantified the bulk optical properties (BOP) of skin, outer cortex, inner cortex, and core tissue of three pear (Pyrus communis) cultivars (Thimo , Cepuna , and Conference) using double integrating spheres measurements in combination with the inverse adding doubling method. Similar trends and values were observed for the bulk optical properties of the three cultivars. A clear chlorophyll-a absorption feature was present in the bulk absorption coefficient (μ a) at 690 nm for the skin samples. At 761 nm, the bulk scattering coefficient (μ s) decreased from the skin towards the core region, for example from 256 ± 34 cm−1 to 146 ± 22 cm−1 for Conference pears. The observed anisotropy factor (g) of the skin was lower than these of the other tissue layers (0.87 ± 0.026 vs. 0.94 ± 0.08 for Conference). Next, Monte Carlo voxelized media (MCVM) simulations were performed based on these BOP values and validated against measurements with a TDLAS setup for gas in scattering media absorption spectroscopy (GASMAS) at 761 nm. In these experiments, the sample thickness was reduced by sequentially slicing the pear from the skin towards the center. Light transmittance through an intact pear at the height of the core region was found to be very low (1.9 × 10−4 ± 8.5 × 10−5%) and exponentially increased around 100-fold when the sample thickness decreased from 64 mm to 24 mm. The simulated transmittance profiles based on the measured BOP values at 761 nm followed the same trend as the measured GASMAS transmittance as a function of the fruit thickness. This shows that simulations based on these measured BOP values can be used to optimize the measurement configuration for O 2 monitoring in intact pear fruit with GASMAS. • The bulk optical properties of pear tissue layers: skin, outer cortex, inner cortex, and core. • 3D Monte Carlo simulation of diffuse transmittance through an intact pear. • Comparison of simulated and measured diffuse transmittance vs pear sample thicknesses. • Simulations provided a valuable tool for optimizing the amplification of GASMAS detectors in diffuse transmittance mode. [ABSTRACT FROM AUTHOR]

The interaction of visible and near-infrared light with citrus tissues is of great importance for the design of new optical sensors for fruit quality inspection. In this study, the light propagation through citrus fruit was simulated using the Monte Carlo multi-layered (MCML) technique based on the bulk optical properties (BOP) of citrus tissues. Comparison of the diffuse reflectance profiles from MCML and from the laser scatter images confirmed the accuracy of the simulations. Simulation results indicated that most of the light was diffusely reflected or absorbed in the flavedo. Only a small fraction around 800 nm was transmitted through the three layers. Flavedo and albedo were found to contribute mostly to the diffuse reflectance spectra at 800 nm and their contributions respectively decreased and increased with source-detector distance. Although the contribution of juice vesicles increased with distance, the maximal diffuse reflectance intensity contributed by juice vesicles was located within 0.56 cm. Based on these results, the combination of the power intensity and the source-detector distance can be optimized to obtain more information about the layer of interest, which lays the foundations for designing new quality detection sensors for citrus fruit. • Light propagation in citrus fruit was simulated by Monte Carlo multi-layered model. • Good agreement of simulated and measured diffuse reflectance profiles. • Light was mainly absorbed by flavedo and diffusely reflected. • Flavedo and albedo contributed mostly to the diffuse reflectance spectra. [ABSTRACT FROM AUTHOR]