Submitted to: Proceedings of SPIE
Publication Type: Proceedings
Publication Acceptance Date: 9/10/2007
Publication Date: 10/12/2007
Citation: Qin, J., Lu, R., Peng, Y. 2007. Internal quality evaluation of apples using spectral absorption and scattering properties. Proceedings of SPIE. 6767:67610M. Interpretive Summary: Absorption and scattering are two basic phenomena when light interacts with turbid or opaque biological materials. Absorption is primarily related to the chemical constituents of the material, whereas scattering is influenced by the density, cell structures and interfaces between cells. Thus measurement and separation of absorption and scattering properties of fruit can provide more information on internal quality of apples. In this research, we measured the absorption and scattering properties of 600 ‘Golden Delicious’ apples in the visible and near-infrared region between 500 and 1000 nm using a spatially resolved hyperspectral imaging technique recently developed in our lab. Mathematical models were developed relating the measured optical properties to apple fruit firmness and soluble solids content. Results showed that absorption and scattering were related to fruit firmness and soluble solids content. The combination of the two properties provided better predictions of fruit firmness and soluble solids content, with the correlation coefficient of 0.88 and 0.82, respectively. This research established an optical property database for ‘Golden Delicious’ apples, and it demonstrated the usefulness of absorption and scattering properties for predicting fruit quality. The research opened a new way for nondestructive sensing of the quality of horticultural and food products. Researchers now can use the method developed in this research to determine the optical properties of other food and agricultural products and then relate them to quality attributes of these products.
Technical Abstract: The objective of this research was to measure the absorption and reduced scattering coefficients 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 the absorption coefficient and reduced scattering coefficient 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 reduced scattering coefficient decreased monotonically with the increasing wavelength. Both absorption and reduce scattering coefficient were correlated with fruit firmness, with the correlation coefficient (r) of 0.82 and 0.80, respectively. Values of the absorption coefficient were also correlated with SSC with r = 0.70. The combined data of absorption and reduced scattering coefficients 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.