Internal quality evaluation of apples using spectral absorption and scattering properties

The objective of this research was to measure the absorption and reduced scattering coefficients (mu(a) and mu(s)', respectively) of apples via a spatially-resolved hyperspectral imaging technique and relate them to fruit firmness and soluble solids content (SSC). Spatially-resolved hyperspectral images were acquired from 600 'Golden Delicious' apples, and values for mu(a) and mu(s)' were determined using an inverse algorithm to fit the diffusion theory model to the spectral scattering profiles over 500-1000 nm. There were two predominant peaks in the absorption spectra around 675 nm and 970 nm due to the presence of chlorophyll and water in the fruit, respectively. Spectra of mu(s)' decreased monotonically with the increasing wavelength. Both mu(a) and mu(s)' were correlated with fruit firmness, with the correlation coefficient (r) of 0.82 and 0.80, respectively. Values of mu(a) were also correlated with the SSC with r=0.70. The combined data of mu(a) and mu(s)' were able to predict fruit firmness with r=0.88 and the standard error of prediction (SEP) of 5.66 N, and SSC with r=0.82 and SEP=0.75%. This research demonstrated the potential of using spectral absorption and scattering properties to evaluate internal quality attributes of horticultural products.