Experimental study of light propagation in apple tissues using a multispectral imaging system

Abstract

This work aimed at highlighting the role played by the skin in the light propagation through the apple flesh. A multispectral Visible-Near Infrared (Vis-NIR) steady-state imaging setup based on the use of four continuous laser sources (633, 763, 784, and 852 nm) and a charge-coupled-device (CCD) camera was developed to record light diffusion inside apple tissues. Backscattering images and light reflectance profiles were studied to reveal optical features of three whole and half-cut apple varieties with and without skin. The optical absorption and scattering properties (μa, μ's) of intact apples and peeled apples were also retrieved in reflectance mode, using an optimal sensing range of 2.8-10 mm. A relative difference for Δμa ranging from 3.4% to 24.7% was observed for intact apples with respect to peeled apples. Under the same conditions, no significant changes were noted for Δm's, which ranged from 0.1% to 1.7%. These findings show that the apple skin cannot be ignored when using Vis-NIR optical imaging as a non-destructive sensing means to reveal major quality attributes of fruits.