Common techniques to monitor the quality of fruit at the time of harvest and in storage typically rely on destructive methods to measure physical properties such as firmness and hydration. The complex, inhomogeneous composition of most fruit mean that non-destructive ultrasonic methods for quality evaluation of fruit has typically been unsuccessful. A novel ultrasound method was developed which analyses the reflections at the transducer-fruit boundary to evaluate the quality of the fruit as a whole. Using a custom-built ultrasound device, the technique was applied to navel oranges to relate ultrasonic measurements with physical measurements taken via destructive methods. For a sample of randomly selected navel oranges, a high level of correlation was found between ultrasonic measurements and the density of the fruit, allowing the relative water content of oranges to be non-destructively determined regardless of individual physical characteristics such as size and maturity. When applied to a sample of navel oranges over a period of nine days, the ultrasonic measurements were found to be highly correlated to the firmness of the oranges, providing a non-destructive method to replace traditional destructive methods currently used to monitor orange maturation. (C) 2014 Elsevier Ltd. All rights reserved.