Electrical Impedance Spectroscopy Investigation on Banana Ripening

The electrical impedance parameters of two varieties of bananas: Cavendish bananas (Musa sp., 'Williams') (AAA) and Lady Finger bananas (Musa sp., 'Lady Finger') (AB) were studied during ripening periods with a Solartron (TM) Impedance/Gain-phase Analyzer and an Hewlett-Packard (TM) LF Impedance Analyzer with a sweeping frequency range of 1 Hz to 1 MHz. Tin-plated copper electrodes and Ag/AgCl electrodes are used in measurements. The Ag/AgCl electrodes show better performance without polarization effects. Fruit peel colours were employed as a routine approach to determine the ripening stages visually. The impedance results were further applied to two previous proposed plant cell electrical models, the Hayden's model and the double-shell model. The double-shell model gives better description of the electrical properties of banana, which shows that the whole fruit impedance, cell wall resistance, and vacuole resistance have positive linear relationships with peel color grade for the Lady Finger bananas. And the whole fruit impedance of Cavendish bananas displayed an increasing trend for the first few days, and a drop in the following two days. The respiration climate during the Cavendish bananas' ripening period are shown directly based on the observed electrical impedance changes. Moreover, the potential application of the findings from this investigation regarding the prediction of fruit storage period is also discussed.