Optical characterization of biological material: A multiscale approach

Abstract

The change of Vis/NIR radiation when propagating through biological material is the result of a complex process of molecule-specific absorptions and multiple light scattering caused by the interaction of the photons with the microstructure. In addition, many biological products, such as fruit or skin tissue are characterized by a layered structure. Therefore, multiple measurements are needed to separate the information on the different layers. In this research, reflectance measurements at different distances from the incident light beam are combined with multiscale light propagation models to extract the compositional and microstructure properties of biological products. First, the biological material is modelled at the macroscale (∼mm) as a set of uniform layers, where the light propagation in each layer is defined by 3 bulk optical properties. Using these 3 bulk properties the reflectance spectra at different distances from the incident light beam are calculated by Monte Carlo simulations for the radiative transport equation. The bulk optical properties of one or two tissue layers in a biological material are then estimated by comparing the measured spatially resolved reflectance profiles to a library of profiles simulated for a wide range of combinations of optical properties. In a second step, the estimated scattering and absorption properties are then related to the chemical composition and microstructure of the different layers. This approach has been applied for the optical characterization of microstructure in food products such as food gels, food foams and chocolate mousse.status: publishe