Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/6/2006
Publication Date: 7/14/2006
Citation: Lu, R., Qin, J., Peng, Y. 2006. Measurement of the optical properties of apples by hyperspectral imaging for assessing fruit quality. ASABE Annual International Meeting. Paper No. 066179.
Interpretive Summary: The interaction of light with turbid biological materials, such as fruit, is a complicated phenomenon that involves both scattering and absorption. Light scattering is influenced by the structural characteristics of the material, such as density, cellular structures and the interfaces between cells. Absorption, on the other hand, is related to the chemical constituents of the material and hence it can be used to probe the chemical properties of product items. Since scattering and absorption are intertwined, they are difficult to measure from intact turbid food and agricultural products. Current methods for measuring the optical properties of biological materials require sophisticated instrumentation and are slow and restrictive in sample preparation. We recently developed a new optical technique using hyperspectral imaging for rapid measurement of the optical properties (absorption and scattering) of turbid materials. Hyperspectral imaging provides both spectral and spatial information over a specific spectral region. In this research, the hyperspectral imaging technique was applied to measure the absorption and scattering properties of 650 'Golden Delicious' apples over the spectral region 530-950 nm. The optical property data were then related to fruit firmness and soluble solids content, two important attributes for apples. Low correlations were found between the optical properties and fruit firmness and soluble solids content. This research represents the first effort of using hyperspectral imaging for determining the optical properties of apples. The optical property data obtained from the research will be useful in quantitative understanding of light interaction with apples and thus in designing a more effective optical method for assessing quality of apples.
Technical Abstract: 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 algorithm and system calibrations are needed for more accurate, reliable measurements of the optical properties of food and agricultural products.