Submitted to: Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2007
Publication Date: 4/15/2007
Citation: Qin, J., Lu, R. 2007. Measurement of the Absorption and Scattering Properties of Turbid Liquid Foods Using Hyperspectral Imaging. Applied Spectroscopy. 61(4):388-396. Interpretive Summary: Measurement of optical properties will provide critical information needed in designing an effective optical system for quality evaluation and safety inspection of food and agricultural products. Light interaction with the turbid and opaque food takes place in the form of absorption and scattering, which are related to the chemical and physical properties of the food. Several techniques have been developed for measuring optical properties of human tissues, but they are not suitable for food and agricultural products because of high instrumentation cost and complicated measurement requirements. In this research, we developed a new technique using hyperspectral imaging for rapid, noncontact measurement of optical properties of food materials. Hyperspectral imaging combines the main features of imaging and spectroscopy, enabling to acquire hundreds of spectra simultaneously. An instrumental calibration method and data processing algorithm were proposed and validated for determining the optical properties of turbid foods. The hyperspectral imaging system was tested with three types of simulation samples with known optical properties and also used to measure the optical properties of milk and several fruit and vegetable juices. The results showed that the optical properties of milk were highly related to its fat content with the correlation coefficient of 0.995 or higher. This research represents the first effort of using hyperspectral imaging for measuring the optical properties of liquid foods, which are largely absent in the literature. Compared to other techniques, the hyperspectral imaging technique is simpler, faster and easier to use, and it is especially suitable for food and agricultural products. The technique will be useful for understanding and quantifying light propagation and absorption in fruit. It also provides researchers a new means for studying and measuring the optical properties of a wide range of solid and liquid foods.
Technical Abstract: This paper reports on the development of a hyperspectral imaging technique for rapid determination of the absorption and scattering properties of turbid liquid foods over the visible and near-infrared region of 530-900 nm. A hyperspectral imaging system in line scanning mode was first tested and validated with three types of simulation samples, and it was then used to measure the optical properties of fruit and vegetable juices and milks. An instrumental calibration procedure was developed to compensate for the nonuniform instrument response of the imaging system. A curve fitting algorithm for a steady-state diffusion theory model was proposed to determine absorption and reduced scattering coefficients from the spatially-resolved hyperspectral reflectance profiles. The hyperspectral imaging system provided good measurement of the absorption and reduced scattering coefficients for the three types of simulation samples with the average fitting errors of 16% and 11%, respectively. The optical properties of the fruit and vegetable juices and milks were determined for the wavelengths of 530-900 nm. Values of the absorption and reduced scattering coefficients at 600 nm were highly correlated to the fat content of the milk samples with the correlation coefficient of 0.995 and 0.998, respectively. Compared to other techniques, the hyperspectral imaging technique is simpler, faster and easier to use, and it is especially suitable for measuring the optical properties of turbid food and agricultural products.