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

Absorption and reduced scattering coefficients are two fundamental optical properties forturbid materials. The objective of this research was to use a newly developed hyperspectral imagingtechnique for determining the absorption and reduced scattering coefficients of apples and to relatethem to fruit firmness and soluble solids content. Hyperspectral images were acquired from 650Golden Delicious apples. The absorption and reduced scattering coefficients of the apples weredetermined using an inverse algorithm to fit the diffusion theory model to individual scattering profilesover the wavelengths of 530-950 nm. Values of the absorption and reduced scattering coefficientswere in the range of 0.0-0.3 cm-1 and 11- 19 cm-1, respectively. For most apples, there was apredominant peak around 675 nm due to chlorophyll absorption. Spectra of the reduced scatteringcoefficient decreased monotonically with the increasing wavelength. Both absorption and reducedscattering 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 inhardware and computational algorithm are needed for more accurate, reliable measurements of theoptical properties of food and agricultural products.