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 xdomestica 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 (ΔR(50Hz)) 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.