DETERMINING RADIO FREQUENCY HEATING UNIFORMITY OF MIXED BEANS FOR DISINFESTATION TREATMENTS

Chickpeas and lentils are two important legumes grown in the U.S. that need phytosanitary treatments before export to several countries, but it is difficult to artificially infest them with live cowpea weevil for radio frequency (RF) treatment validation. To evaluate the more readily infested black-eyed peas and mung beans as surrogates for chickpeas and lentils, the thermal and dielectric properties of black-eyed peas and mung beans at selected moisture contents were measured and compared with those of chickpeas and lentils. Temperature differences between black-eyed pea and chickpea or between mung bean and lentil were determined in a pilot-scale 27 MHz RF unit. The results showed that the dielectric constant and loss factor of black-eyed pea and mung bean increased with increasing moisture content and temperature, which was in good agreement with the trends observed in chickpea and lentil. After 6 min of RF heating, temperatures in black-eyed pea (moisture content of 8.8% w.b.) were 6 degrees C higher than those in chickpea (moisture content of 7.0% w.b.), while after 10 min of RF heating mung bean temperatures (moisture content of 10.2% w.b.) were 4 degrees C higher than lentil temperatures (moisture content of 7.1% w.b.) under the same treatment conditions. By reducing the moisture contents in black-eyed pea and mung bean to 2.6% and 3.7% w.b., respectively, their final temperatures were about 3.5 degrees C and 3.7 degrees C lower than those of chickpea and lentil. This would result in conservative insect mortality results when using black-eyed pea and mung bean as surrogate hosts for validation of pest control treatments in chickpea and lentil.