A number of methods for quality evaluation and sorting of agricultural products have been developed by different researchers over the past three decades. These methods are based on the detection of various physical properties which correlate well with certain quality factors of the products. This paper presents an overview of various methods which are based on one of the following properties: density, firmness, vibrational characteristics, X-ray and gamma ray transmission, optical reflectance and transmission, electrical properties, and nuclear magnetic resonance, NMR. The sophistication of non-destructive methods has evolved rapidly with modern technologies. Optical methods which utilize high-speed optical detection and computerized data processing are the most successful methods which can provide high-speed quality evaluation and sorting of several products with a high degree of accuracy. The use of various modern image acquisition techniques, such as solid-state TV camera, line-scan camera, X-ray scanning, ultrasonic scanning, and NMR imaging, in conjunction with image processing techniques has provided new opportunities for researchers to develop many new and improved techniques for non-destructive quality evaluation of agricultural products. © 1991 The British Society for Research in Agricultural Engineering.
