Selection of cole model bio-impedance parameters for the estimation of the ageing evolution of apples

Abstract

Electrical impedance spectroscopy (EIS) is an emerging, fast, reliable and non-destructive technique for fruit quality assessment. In this paper, bio-impedance spectroscopy (BIS) measurements were carried out to monitor apple ageing evolution during a 12 days period using a microcontroller-based system. The data was extracted in the 100 Hz-85 kHz frequency range and the resulting impedance spectra were fitted with the Cole equivalent circuit. The four variables of the circuit, namely series and parallel resistance (Rs and Rp) and constant phase element (CPE) magnitude and phase, were extracted from the model and evaluated in terms of their correlation with the studied fruit ageing evolution. The results indicated that the parallel resistance (Rp) decreasing trend is useful to cluster the apples according to the ageing stage, while the CPE parameters allow discriminating among single fruits physiological conditions at the same maturity stage.