Feasibility of physical properties and soft X-ray attenuation properties for non-destructive determination of quality of nutmeat in in-shell pecans

Scope and method of study. The purpose of this study was to investigate the physical and X-ray attenuation properties of pecans for non-destructive quality evaluation of ‘in-shell’ pecans. The work included determination of physical properties vis-à-vis, size, shape, and specific gravity of the whole nut, nutmeat, and shell. Equipment was developed for high-resolution (1024 x 1024 pixels) digital X-ray imaging of pecans with soft X-rays (less than 50 kVp). Pecans with known internal defects were fabricated for initial testing. X-ray images of pecans were obtained at 80 combinations of X-ray tube voltage and current, and combinations were found for best image quality. Further testing was done on natural pecans of ‘unknown’ quality. Nutmeat quality features were determined from pecan X-ray images taken at six X-ray energy levels.; Findings and conclusions. Physical properties of pecans varied with equilibrium relative humidity and cultivar. Pecan size increased in all three dimensions at higher humidity. Specific gravity of shell was higher than nutmeat. The developed imaging system is able to capture radiographs of a sample not larger than 50 x 50 x 125 mm. X-ray tube parameters could be controlled precisely to capture images at an integration time of 460 ms or more. The linear attenuation coefficient of pecan shell was higher than that of nutmeat. Attenuation coefficient varied with X-ray tube peak voltage and sample thickness. A regression model with R2 more than 0.9 was developed to predict attenuation coefficient at a given voltage and nutmeat thickness. Percent nut area, mean pixel intensity, and local intensity variation adequately determined nutmeat quality, non-destructively. Pecan nutmeat weight was estimated with an error of less than 10% from images taken at 35 kVp-0.75 mA, 40 kVp-0.5 mA, and 45 kVp-0.5 mA. Defects and insects were clearly differentiated in X-ray images after applying contrast stretching or high-frequency emphasis techniques.