Bioimpedance Measurement of Avocado Fruit Using Magnetic Induction Spectroscopy

Abstract

Avocado fruit is a popular, nutritious, and commercially valuable product that, with a short window of ripeness and heterogeneous maturity, presents particular challenges when bringing to market. There is significant value in being able to measure avocado fruit ripeness and maturity, especially nondestructively, with the prospect of improvements in consignment management, food loss, and consumer satisfaction. In this article, we explore the bioimpedance spectra of avocado fruit. Bioimpedance has been found to correlate with ripeness in avocado fruit over a frequency range termed the $\beta$ -dispersion where cell polarization effects are significant. Our contribution is to use magnetic induction spectroscopy to measure conductivity across this range, an entirely noncontact method that uses eddy currents induced in the fruit flesh by magnetic fields rather than penetrative or surface electrodes as in previous work. We were able to measure a clear $\beta$ -dispersion curve, finding fruit conductivity rising from $\sim$ 0.6 mS/cm at 100 kHz to $\sim$ 4 mS/cm at 10 MHz. This agrees with the literature at higher and lower frequencies, and completes a gap in the spectra not previously reported. Further, we find evidence of changes to the conductivity spectra as the fruit ages and ripens, with the spectra broadly flattening according to a set of identified trends. This indicates a relation between bioimpedance spectra and ripeness, although high intersample variability precludes the spectra as a direct estimation technique at this stage.