Disease and insect pest controls in rice bran and mango by radio frequency heat treatment

Abstract

Radio frequency (RF) is an electromagnetic radiation that greatly dissipates heat through the thick material, then it has been applied in the heating process with materials containing water element. The principle uses is based on heat generated by using electromagnetic field in performance of radio frequency emissions through a dipole molecular of the object of which causes the heat generated within a short time. Therefore, this study has developed RF techniques to increase the value of agricultural raw materials in different type of orthodox and recalcitrant material. Low moisture containing as orthodox material was represented as rice bran sample which contain high fatty acid and always caused rancidity during storage especially purple rice bran comprising with nutraceutical composition. The objective was to find out appropriate and effective RF technique for extending the rancidity of the purple rice bran and determined the responsibility of the bran to the RF technique. The recalcitrant material or high humidity is used mango fruit as a representative because of their high value of export fruit of Thailand. However, the mango faced with fruit fly infestation and needed to eradicate by soaking in hot water for approximately 90°C. RF technique is an alternative use to eliminate the fly, but the heat treatment with fresh fruit has been reported that the damage has been observed at the point of contact with container and fruit at each touch point, the research was to develop and create a prototype application of the turntable with a container of water to improve the uniformity of the RF heat and determined appropriate method through trial with different dielectric property of mango. The experiment was also measured the performance of the techniques on controlling insects pest contaminated in mango fruit which have approved through preliminary research of elimination of fruitfly (Batrocera dorsalis (Handel); Tephrididae: Diptera) contaminated with raw mangoes without adverse effect on the fruit. The qualities of mangoes after RF heating to control fruit flies were also tested. The development of RF to add value in agricultural raw materials with low moisture such as rice bran 4 cultivars (glutinous rice cv. Sanpatawng1, non-glutinous rice Kaw Dok Mali 105, purple rice cv. Kam Doi Saket and Kam Nan) treated with RF (27.12 MHz) with temperature of 70, 75 and 80°C for3 minutes and packed under vacuum seal, then stored for 6 months at 25°C showed that the RF heat decreased rice bran moisture content (about 1 percent) and the rancidity of rice decreased significantly (p≤0.05). However, after two months storage, the water retention increased moisture content to the equilibrium. The temperature of 70 and 75ºC significantly decreased the microbial contamination in rice bran samples. After storage for2-6months, the oil content significantly increased from the previous storage. The rancidity measured by TBA value increased with the storage time through 4 months after that it decreased until 6 months. The interaction between temperature and rice cultivars significantly affected on change of TBA value by RF heating at 75 and 80ºC rice bran showed the lowest TBA value. As well as the techniques resulted in a large amount of anthocyanin extraction of rice bran cv. Kam Nan which was significant increased. Consequently, the further study was to investigate higher temperature 80, 100 and 120ºC for 5 minutes) of RF heat treatments for alternative stabilization technique in rice bran 2 cultivars (non-glutinous rice cv. Khaw Dawk Mali 105; KDML 105 and glutinous rice cv. San Pa Twang 1; SPT1) and stored in two different packaging conditions (pressure 70 and-100 kPa) for 3 months. Before and after storage for each 1 month, the chemical compositions and enzyme lipase activity were determined. The result found that after treating, the moisture of both cultivars significantly decreased while the oil and protein content was unchanged. The lipase enzyme and rancidity significantly decreased with increasing of treated temperatures. After storage for 3 months, the moisture of all bran in both packing increased due to equilibrium moisture activity. Storage of 1 month also resulted in TBA value of bran packed in 70 kPa sealer especially the sample treated at 80ºC showed the highest value (18mg MDA/kg rice bran) whereas the value of bran closed in -100 kPa was unchanged. Moreover, the stabilized rice bran using RF application was influenced the activity and stability of lipase by using temperature of 100 and 120ºC could also retain 17-26% of the maximal activity of lipase enzyme in untreated rice bran. Development of RF techniques to increase the value of agricultural raw materials with high humidity such as the removal of fruit fly contaminated in mango found that dielectric property (dielectric constant and loss factor) of mango 3 cultivars (Nam Dok Mai, Chok Anan and Fa Lun) dipped in water at temperature of 35, 40 and 50ºC for 30, 60 and 90 minutes decreased with increasing of frequency but increased with increasing temperature and time. Moreover, development of the prototype turntable disc with a container of water combined with RF power of 1,000 watt for 3-5 minutes possibility improved heat uniformity inside the mango fruit by using water as conductor. The heat distribution showed higher performance than mango treated with hot air method and the uniformity of heat was similarly to mango dipped in water at temperature of 46ºC for 90 minutes of which the mango showed no bruises or burn caused by heat. The next experiment was further carried out to control fruit fly contaminated in mango fruit by using RF heat treatment at temperature of 48°C for 4, 6 and 8 minutes compared with standard method (dipping in hot water temperature of 46°C for 90 minutes). After exposure to RF application, the mango samples were tested for qualities. The results showed that RF heating technique completely reduced the contamination of eggs and larvae in mango fruit fly which equivalent to the standard method and the physical condition of mangos remain unchanged as well as both methods showed no effect on sweetness of the fruit. The use of heat at48°C for 8 minutes did not affect on the pH of mango which the result similarly to the standard method.