This study demonstrates that the ripeness of avocado fruits can be analyzed using frequency-dependent electrical conductivity and permittivity through a non-invasive Magnetic Induction Spectroscopy (MIS) method. Utilizing an MIS system for conductivity and permittivity measurements of a large sample set ($N=60$) of avocado fruits across multiple frequencies from 100 kHz to 3 MHz enables clear observation of their dispersion behavior and the evolution of their spectra over ripening time in a completely non-contact manner. For the entire sample batch, the conductivity spectrum exhibits a general upward shift and spectral flattening over ripening time. To further quantify these features, normalized gradient analysis and equivalent circuit modeling were employed, and statistical analysis confirmed the correlations between electrical parameters and ripening stages. The trend characteristics of the normalized gradient parameter $P_y$ provide a basis for defining the three ripening stages within the 22-day period: early pre-ripe stage (0–5 days), ripe stage (5–15 days), and overripe stage (after 15 days). The equivalent circuit model, which is both physically interpretable and fitted to experimental data, revealed that the ripening process of avocado fruits is characterized by a weakening of capacitive structures and an increase in extracellular solution conductivity, suggesting changes in cellular integrity and extracellular composition, respectively. The results also highlight significant inter-sample variability, which is inherent to biological samples. To further investigate individual conductivity variation trends, Gaussian Mixture Model (GMM) clustering and Principal Component Analysis (PCA) was conducted for exploratory sample classification and visualization. Through this approach, the sample set was classified into three categories, each corresponding to distinct conductivity variation patterns.

This work explores the application of Magnetic Induction Spectroscopy (MIS) as a tool for phenotyping cellular structural degradation in biological tissues, specifically plant parenchyma. The principal advantage of MIS is its non-contact operation, whereby induced eddy currents probe bulk electrical properties without physical or electrical contact, avoiding electrode-interface artefacts and sample perturbation. A previously developed differential-coil MIS sensor, with sensitivity optimised via a tuned passive network, was used to measure conductivity spectra from 70 kHz to 9 MHz. Avocado fruit, potato, and apples were subjected to three freeze-thaw cycles as a controlled model of cellular structural degradation. Across the three tissue types, freeze-thaw treatment progressively attenuated the conductivity dispersion, consistent with weakened Maxwell-Wagner interfacial polarisation and loss of cellular compartmentalisation. Correspondingly, dispersion indices, including the model-fitted conductivity dispersion magnitude, Δσ, and the ratio between the low- and high-frequency conductivity, Py, decreased, with Py falling by 40–95% from the fresh state to the third cycle. Bright-field microscopy independently confirmed progressive disruption of cellular boundaries and tissue organisation. These results support that MIS-derived dispersion metrics can provide a quantitative, label-free, non-contact, and volumetric indicator of cellular degradation in bulk biological tissues, with potential applications in biological and agri-food quality assessment.