Apple Bruise Detection by Electrical Impedance Measurement

Abstract

Electrical impedance was used to determine the extent of tissue damage that occurred as a result of bruising of apple fruit (Malus ×domestica Borkh, cvs. Granny Smith and Splendour). Impedance measurements were made before and after bruising. Plots of reactance against resistance at 36 spot frequencies between 50 Hz and 1 MHz traced a semicircular arc, which contracted in magnitude after bruising. A number of characteristics of these curves were then related to bruise weight. The change in resistance that occurred as a result of fruit impact (ΔR50Hz) was the best predictor of bruise weight, with r2 values up to 0.71. Before bruising, resistance of fruit was higher in `Splendour' than in `Granny Smith' (P < 0.001), and at 0 °C than at 20 °C (P < 0.001), but was not influenced by fruit weight. The influence of apple cultivar and temperature on electrical impedance may cause difficulties when implementing these measurements in a commercial situation. However, further development of electrical impedance spectroscopy methodologies may result in convenient research techniques for assessing bruise weight without having to wait for browning of the flesh.