Abstract
An electronic method to estimate the moisture content (MC) of dry fruits by measuring the impedance (Z) and phase angle (θ) of a cylindrical parallel-plate capacitor with dry fruit sample between the plates, using a CI meter (Chari’s Impedance meter) at 1 and 9 MHz is described. Capacitance C was derived from Z and θ, and using the C, θ, and Z values of a set of dried cherries, whose MC values were later determined by the vacuum hot air-oven method, a calibration equation was developed. Using this equation, and their measured C, θ, and Z values, the MC of a group of cherries, not used in the calibration, was predicted. The predicted values were compared with their air-oven values. Similar predictions were done using the same method on dried blueberries. The method worked well with a good R2 value, and showed a low standard error of prediction (SEP) in the measured MC range between 5% and 30% for cherries, and 9% and 22% for blueberries.
Highlights
Dry fruit is fruit from which the majority of the original moisture content (MC) has been removed either naturally, or through the use of hot air dryers or dehydrators
The capacitance of a parallel-plate capacitor with plate area A and plate separation d, filled with a dielectric material, at a frequency f1 is given by: C1 = εr1ε0A d and at a frequency f2 is given by: C2 = εr2ε0A d εr1 and εr2 are the dielectric constants of the dielectric material at the two frequencies and ε0 is the permittivity of free space (8.854 × 10−12 farad/m)
Capacitance, phase angle and dissipation factor were measured on single kernels with each kernel between, and in contact with the two parallel plates at the two frequencies, 1 and 4.5 MHz, and the differences in the values of C, θ, and D were used in an empirical equation, to calculate the MC of the peanut sample placed between the plates
Summary
Dry fruit is fruit from which the majority of the original moisture content (MC) has been removed either naturally, or through the use of hot air dryers or dehydrators. (2015) Nondestructive Determination of Moisture Content in Dry Fruits by Impedance and Phase Angle Measurements. An electronic method is described here for the rapid and nondestructive measurement of the MC of dry fruits from the measurement of impedance and phase angle of a parallelplate capacitance, holding about 100 g of the fruit sample between the plates. The method worked successfully for cherries and blueberries, and can be extended to other types of fruits such as raspberries
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