Use of Radio Frequency for Controlling Sawtoothed Grain Beetle (<I> Oryzaephilus surinamensis </I>) in Milled Rice cv. Khao Dawk Mali 105

Abstract

The objectives of this experiment were to use radio frequency (RF) for controlling sawtoothed grain beetle (Oryzaephilus surinamensis) in milled rice cv. Khao Dawk Mali 105 and to examine rice quality after treated by radio frequency with appropriate rate which performed completely kill insects. The experiment was conducted at Postharvest Technology Research Institute, Chiang Mai University, Thailand. Insect mass rearing in milled rice cv. Khao Dawk Mali 105 with moisture content at 14% was conducted in laboratory condition. In experiment 1, all developmental stages of insect, egg, larva, pupa and adult were treated by 27.12 MHz radio frequency which provided 55^oC for 90 seconds. The result showed that adult stage of sawtoothed grain beetle was the most tolerance to RF heat treatment because adult mortality was the lowest (78.09%) (P<0.05), followed by the mortality of pupal, larval and egg stages which were 90.90, 94.34 and 96.46%, respectively. In experiment 2, adult stage of sawtoothed grain beetle, the most tolerant to RF heating, was exposed to RF at 55, 60, 65 and 70^oC for 90, 120, 150 and 180 seconds at each temperature. The result found that RF treatment at 70^oC for 120 seconds was able to get effective control of sawtoothed grain beetle since there was the minimal combination rate of RF heat and there was no insect progeny found in milled rice. Moisture content and protein content of milled rice decreased when it was treated with RF and the yellowness and whiteness index also decreased while amylose content has increased. The amount of 2-acetyl-1-pyrroline (2-AP), the aroma compound which always found from fragrant rice was decreased from 2.82 ppm to 2.40 ppm after the RF heat treatment on Khao Dawk Mali 105 milled rice.