Current pesticides such as methyl bromide are progressively removed from the market due to harmful residues in food. The stone fruit industries are thus seeking alternatives for postharvest control of insect pests. Microwave and radio frequency methods hold potential for postharvest thermal disinfestations of stone fruits to replace chemical fumigation. Knowledge of dielectric properties is essential for understanding the interaction between the electromagnetic fields and the target stone fruits and designing treatment beds in industrial applications. Here, we determined the dielectric properties of nectarine, peach, and plum between 10 and 1,800 MHz over a temperature range of 20–60 °C using an impedance analyzer. Our results show that the dielectric constant generally varied between 60 and 75, accounting for changes of 8–10 % due to temperature effect. But, the loss factor decreased linearly with frequency on the log scale at all temperatures for three stone fruits. The loss factor of Mediterranean fruit fly, nectarine, peach, and plum increased about 106, 108, 110, and 64 %, respectively, when the sample temperature increased from 20 to 60 °C. The penetration depth in all stone fruits decreased with increasing frequency and temperature. The loss factor ratio at 27 MHz of Mediterranean fruit fly to nectarine, peach, and plum was 1.65, 1.66, and 1.87 at 20 °C, respectively, suggesting potential differential heating between insects and host stone fruits in radio frequency treatments.
Dielectric properties Differential heating Disinfestations Open-ended coaxial probe Stone fruit
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This research was conducted in the Department of Biological Systems Engineering, Washington State University (WSU), supported by grants from WSU Agricultural Research Centre, and partially provided by the general program of the National Natural Science Foundation of China (No. 31371853).
[USDA-NASS] United States Department of Agriculture-National Agricultural Statistics Service (2012) National statistics of crops. http://www.nass.usda.gov/ QuickStats/index2.jsp, Washington, DC. Accessed 12 Nov 2013
AlFaifi B, Wang S, Tang J, Rasco B, Sablani S, Jiao Y (2013) Radio frequency disinfestation treatments for dried fruit: dielectric properties. LWT–Food Sci Technol 50(2):746–754. doi:10.1016/j.lwt.2012.07.012Google Scholar
Andreuccetti D, Bini M, Ignesti A, Gambetta A, Olmi R (1994) Microwave destruction of woodworms. J Microwave Power Electromag Ene 29(3):153–160Google Scholar
AOAC (2002) Fruits and fruit products. In: Official methods of analysis of the Association of Official Analytical Chemists, 17th edn (Horwitz W eds). Gaithersburg, MD, USA: AOAC: AOAC InternationalGoogle Scholar
Komarov V, Wang S, Tang J (2005) Permittivity and measurement. In: Chang K (ed) The Wiley encyclopedia of RF and microwave engineering, vol 4. John Wiley & Sons, Inc, New York, pp 3693–3711Google Scholar
Nelson SO (1996) Review and assessment of radio-frequency and microwave energy for stored-grain insect control. Trans ASAE 39:1475–1484CrossRefGoogle Scholar
Nelson SO (2003) Frequency- and temperature-dependent permittivities of fresh fruits and vegetables from 0.0 l to 1.8 GHz. Trans ASAE 46:567–576CrossRefGoogle Scholar
Nelson SO (2005) Dielectric spectroscopy of fresh fruit and vegetable tissues from 10 to 1800 MHz. J Microwave Power Electrom Ene 40(1):31–47Google Scholar
Nelson SO, Charity LF (1972) Frequency dependence of energy absorption by insects and grain in electric fields. Trans ASAE 15(6):1099–1102CrossRefGoogle Scholar
Nelson SO, Payne JA (1982) RF dielectric heating for pecan weevil control. Trans ASAE 31:456–458CrossRefGoogle Scholar
Nelson SO, Stetson LE (1974) Comparative effectiveness of 39– and 2450–MHz electric fields for control of rice weevils in wheat. J Econ Entomol 67(5):592–595Google Scholar
Peng J, Tang JM, Jiao Y, Bohnet SG, Barrett DM (2013) Dielectric properties of tomatoes assisting in the development of microwave pasteurization and sterilization processes. LWT–Food Sci Technol 54(2):367–376. doi:10.1016/j.lwt.2013.07.006Google Scholar
Sosa-Morales ME, Tiwari G, Wang S, Tang J, Lopez-Malo A, Garcia HS (2009) Dielectric heating as a potential post-harvest treatment of disinfesting mangoes. I: Relation between dielectric properties and ripening. Biosystems Eng 103(3):297–303. doi:10.1016/j.biosystemseng.2009. 02.015CrossRefGoogle Scholar
Sosa-Morales ME, Valerio-Junco L, Lόpez-Malo A, Garcίa HS (2010) Dielectric properties of foods: reported data in the 21st century and their potential applications. LWT–Food Sci Technol 43:1169–1179. doi:10. 1016/j.lwt.2010.03.017Google Scholar
von Hippel AR (1954) Dielectric properties and waves. John Wiley, New YorkGoogle Scholar
Wang S, Tang J, Cavalieri RP, Davis D (2003a) Differential heating of insects in dried nuts and fruits associated with radio frequency and microwave treatments. Trans ASAE 46:1175–1182Google Scholar
Wang S, Tang J, Johnson JA, Mitcham E, Hansen JD, Hallman G, Drake SR, Wang Y (2003b) Dielectric properties of fruits and insect pests as related to radio frequency and microwave treatments. Biosystems Eng 85(2):201–212. doi:10.1016/s1537-5110(03)00042-4CrossRefGoogle Scholar
Wang S, Monzon M, Gazit Y, Tang J, Mitcham EJ, Armstrong JW (2005) Temperature-dependent dielectric properties of selected subtropical and tropical fruit and associated insect pests. Trans ASAE 48:1873–1881CrossRefGoogle Scholar