Measurement of the Optical Properties of Apples by Hyperspectral Imaging for Assessing Fruit Quality

Absorption and reduced scattering coefficients are two fundamental optical properties for turbid materials. The objective of this research was to use a newly developed hyperspectral imaging technique for determining the absorption and reduced scattering coefficients of apples and to relate them to fruit firmness and soluble solids content. Hyperspectral images were acquired from 650 ‘Golden Delicious’ apples. The absorption and reduced scattering coefficients of the apples were determined using an inverse algorithm to fit the diffusion theory model to individual scattering profiles over the wavelengths of 530-950 nm. Values of the absorption and reduced scattering coefficients were in the range of 0.0-0.3 cm-1 and 11- 19 cm-1, respectively. For most apples, there was a predominant peak around 675 nm due to chlorophyll absorption. Spectra of the reduced scattering coefficient decreased monotonically with the increasing wavelength. Both absorption and reduced scattering coefficients were correlated with fruit firmness, with the correlation coefficient of 0.56-0.66. Poor correlation between fruit soluble solids content and the absorption coefficient was obtained, which could be due to relatively high fitting errors for the absorption coefficient. Improvements in hardware and computational algorithm are needed for more accurate, reliable measurements of the optical properties of food and agricultural products.