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To facilitate the design of new optical measurement systems for biological systems, the knowledge of light propagation properties is essential. Therefore, the bulk optical properties of skin and cortex of three apple cultivars were studied during maturation, in the 500 nm–1850 nm range. A clear absorption signature was observed with absorption peaks which can be related to present anthocyanins, chlorophyll, carotenoids and water. During maturation, the skin absorption at 550 nm increased in the bicolored cultivars ‘ Braeburn ’ and ‘ Kanzi ’, while the absorption at 680 nm decreased in the cortex. Both the bulk scattering coefficient and the anisotropy factor were larger for the skin compared to the cortex tissue. Also during maturation, the skin scattering increased in the two bicolored cultivars, while a general decrease was seen in the apple cortex. Physiological changes during maturation, like cell growth, the formation/degradation of pigments and the formation of a cuticle layer on the skin, may explain the observed evolutions. As a result, using the bulk optical properties, these physiological changes can be monitored and linked to the maturity stage in the orchard, supporting the selective harvest of apples. [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]