Optical sensing of the storage potential of fruit

To be able to deliver good quality fruits throughout the year, pears are stored under controlled atmosphere. Pear fruit are particularly susceptible to browning disorders, which represent a major source of postharvest losses, as the fruit can no longer be commercialised. It has been hypothesized that the porosity of the fruit could have a large impact on the susceptibility to browning. Therefore, this PhD aims at the development of a fruit porosity sensor. As light propagation through fruit tissue is determined by the absorption and scattering properties of the tissue, which are related to the chemical composition and the microstructural properties of the fruit, it is hypothesized that the porosity has a large impact on the scattering properties. Therefore, information on the tissue porosity, and hence gas diffusivity, might be acquired non-destructively by means of optical measurements. However, one single diffuse reflectance or transmittance measurement is not sufficient to accurately separate the information on the chemical composition and the microstructure. This separation can be realized by combining multiple spectral measurements resolved in space, a technique known as spatially resolved spectroscopy (SRS). To extract the information on the absorption and porosity properties of the pome fruit tissue from the acquired SRS signals, a multiscale light propagation model will be elaborated to simulate the diffuse reflectance at different distances from the point of illumination for tissues with different pore size distributions, porosity, refractive indices of medium and scatterers. The SRS measurements at small source-detector distances will be used for the estimation of the optical properties of the first layer. These estimated properties for the first layer will then be used to estimate the properties of the second layer from the measurements at longer source-detector distances. Further, the porosity sensor will be built following the optimal design as close as possible for validation purposes. This sensor will then be used to measure a set of fruits where large variation in the porosity parameters is expected.