Nondestructive determination of the quality of Red Bartlett pear during shelf life by electrical characteristics

Electrical parameters of Red Bartlett pear fruits were non-destructively measured during seven-day shelf-life storage at 20℃ over a frequency range from 100 Hz to 5 MHz with a parallel-plate copper electrode and HIOKI 3532-50 LCR meter. Fruit firmness and soluble solids content were measured as quality attributes for correlation with the dielectric properties. The optimum frequency for electrical properties test was identified. The results showed that with the increase of frequency, fruit impedance and inductance decreased in exponential form, while capacitance and conductance were changed irregularly. Fruit impedance and inductance decreased significantly（P=0.01）with fruit ripening, while capacitance and conductance changes had an increasing trend. Within 100 Hz～1 MHz frequency, the correlation coefficient between fruit impedance, inductance, capacitance and fruit firmness increased from 0.45, 0.45 and 0.37 at 100 Hz to 0.84, 0.83 and 0.73 at 1 MHz, respectively, while decreased or not changed significantly at the frequency above 1 MHz. Impedance, capacitance and inductance can be taken as the electrical indices for fruit ripeness, and 1 MHz is the optimum test frequency.