Prediction of Apple Internal Quality Using Spectral Absorption and Scattering Properties

The objective of this research was to measure the absorption and reduced scattering coefficients ( a and 's, respectively) of apples using a newly developed spatially resolved hyperspectral imaging technique and relate them to fruit firmness and soluble solids content (SSC). Spatially resolved hyperspectral scattering images were acquired for 600 'Golden Delicious' apples, and values for a and 's were determined using an inverse algorithm to fit the spectral scattering profiles with a diffusion theory model over the wavelengths of 500-1000 nm. The absorption spectra were characterized by two predominant peaks around 675 nm and 970 nm due to the presence of chlorophylls and water in the fruit, respectively. Values of 's for most apples decreased with the increasing wavelength. Both a and 's were correlated to fruit firmness and SSC, but higher correlations were obtained with a than with 's. The combined data of a and 's gave better predictions of fruit firmness and SSC with values for the correlation coefficient (r) of 0.857 and 0.754, respectively. In comparison, a simpler method of calculating relative mean spectra from the hyperspectral scattering profiles gave comparable firmness predictions (r = 0.844) and better SSC predictions (r = 0.864). The spatially resolved technique provides an efficient means for measuring the optical properties of fruit, and it is also useful for assessing fruit quality attributes.