DETERMINATION OF SINGLE-DATE WATER CONTENT BY A NOVEL RF DEVICE

Abstract

In Israel, ‘Madjhool’ has become the major date variety, thanks to its large size and pleasant appearance, which attract buyers who pay a price that is double or more than that of other varieties. However, this variety has a short shelf life and a tendency to develop “skin blisters.” Because of these limitations the growers plan to increase the proportion of fruit marketed as “Fresh Madjhool” – dates that are partially dried before delivery. The main physical property that has to be measured and controlled is fruit water content, and a novel instrument has been developed for this, based on the dielectric effect. Four round flat electrodes are manually positioned so that they touch the date and gently press on it. The electrodes and date constitute a unique capacitor. An RF signal is transmitted through the fruit, and its characteristics are correlated to water-content data. Calibration measurements with this instrument indicated an accuracy of ±2% wet basis (wb). This accuracy enables a representative accumulative distribution chart to be drawn, based on measurements on a sample of 50 fruits. On the basis of such charts several managerial quality decisions can be implemented. The device is controlled by a microprocessor that performs data collection and calculates the average water content of the measured sample. Four prototypes were built and have been tested in several warehouses, where they have yielded useful results.