Relating X-ray Absorption to Density and Water Content in Apples

X-ray computed tomography (CT) was used to image interior regions of ‘Red Delicious’ apples under varying moisture and, to a limited extent, density states. Images were actually maps of x-ray absorption of fruit cross-sections. X-ray absorption properties of ‘Red Delicious’ apples were evaluated using normal apples alternately scanned and sequentially freeze dried, fruit affected by watercore disorder, and normal apples freeze-dried to varying levels. The studies were designed to allow quantification of the x-ray absorption coefficient associated with the dry solids portion of the fruit and the x-ray absorption coefficient associated with moisture. The coefficients associated with moisture were in the vicinity of 0.0191 mm–1 and 0.0182 mm–1, the expected value for water and ice, respectively. The coefficient associated with the dry solids was not significant from zero, due in part to scanner resolution limits, limited dynamic range in density values, and to variation in the physical density measurements. The results of this study suggest that internal differences in x-ray absorption within scans of fruit cross-sections are largely associated with differences in volumetric water content.