Electrical Impedance of Kiwi Fruit

Study on Electrical Quality Evaluation of Fruits and Vegetables Part I

Abstract

Complex impedance of kiwi fruit during ripening was measured at the frequency range from 200Hz to 500kHz. The diagram of impedance locus showed an arc of a circle and characteristic of Cole-Cole dispersion system, which indicated the validity of the calculation of the impedance parameters on the basis of the equivalent circuit for the biological medium. Some of the parameters thus obtained changed remarkably with ripening. The variation of impedance parameters during ripening was different from that by puncturing fruit with a pin. This shows the mechanism of the softening of fruit by ripening is different from that by puncturing. Several impedance parameters were correlated with firmness of fruit. And among them 'Radius' of the arc resulted the maximum coefficient of correlation of 0.895. These results indicated that impedance measurement was promising for quality evaluation of kiwi fruit. It was speculated that the variation of R₂, r₀ and c₀ in the equivalent circuit was caused by both the lowering of selective permeability of cell membrane and the degradation of cell wall as ripening.