Spectral Absorption and Scattering Properties of Normal and Bruised Apple Tissue

Abstract

Knowledge of the spectral absorption and scattering properties of apple tissue, especially bruised tissue, can help us develop an effective inspection method for detecting bruises during postharvest sorting and grading. This research was aimed at determining the optical properties of normal and bruised apple tissue for the wavelength range of 500-1,000 nm and quantifying their changes with time after bruising. Values for the absorption and reduced scattering coefficients were determined for the normal or unbruised tissue of 'Golden Delicious' and 'Red Delicious' apples and then for the bruised tissue, for different time intervals after bruising, using a hyperspectral imaging-based spatially resolved technique. Bruising caused changes to the absorption coefficient, but no consistent pattern of changes was observed for 'Golden Delicious' and 'Red Delicious' apples after they were bruised. The reduced scattering coefficient for normal apples, however, was much higher than that for bruised apples; it decreased consistently with time after bruising. These results suggest that bruising has a greater impact on scattering than on absorption. Hence, an optical system that enhances scattering feature measurement would be better suited for bruise detection.