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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Quality and Safety Assessment Research Unit » Research » Publications at this Location » Publication #318900
Title: Dielectric properties of dried vegetable powders and their temperature profile during radio frequency heating

Author
item OZTURK, SAMET - University Of Georgia
item KONG, FANBIN - University Of Georgia
item Trabelsi, Samir
item SINGH, RAKESH - University Of Georgia

Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2015
Publication Date: 1/15/2016
Citation: Ozturk, S., Kong, F., Trabelsi, S., Singh, R.K. 2016. Dielectric properties of dried vegetable powders and their temperature profile during radio frequency heating. Journal of Food Engineering. 160: 91-100.

Interpretive Summary: Low-moisture foods are commonly used for various applications in the food industry. In the last decade, Salmonella contamination in low-moisture foods, including powdered vegetables and infant formula, dry fruit, nuts, and spices, has become a major safety concern. An outbreak of Salmonella was reported in broccoli powder used for coating snack foods. The high heat resistance of Salmonella in low-moisture foods makes pasteurization of dried foods difficult. The conventional pasteurization methods such as steam and hot air heating require long processing times because of slow heating rates, leading to severe food quality degradation. Radio-frequency (RF) dielectric heating is a rapid, volumetric heating technique that offers a potential alternative pasteurization method with short heating time that may result in improved final product quality and reduced costs. To develop an effective RF pasteurization method for food products, it is important to understand the behavior of their dielectric properties, the major factors characterizing the interaction between the electromagnetic energy and the food materials. Several studies have been conducted to investigate the dielectric properties of various food materials such as grain, seeds, flour, and coffee. The dielectric properties of these materials and the RF heating rate are mainly dependent on moisture content, temperature, and bulk density of the materials and the applied frequency of the electric fields. Therefore dielectric properties of broccoli powder were measured and RF heating rate in the broccoli powder was determined by using a commercial 27.12-MHz, 6-kW RF oven. The results showed that the dielectric constant, e', and loss factor, e'', of broccoli powder were influenced by moisture content and temperature of the material as well as the applied frequency. Both the dielectric constant and loss factor increased with increasing moisture content and temperature, but decreased with increasing frequency. The relationship between moisture content, temperature and dielectric properties of broccoli powder at 13.56 and 27.12 MHz were described by quadratic models. The RF heating rate increased linearly with dielectric loss factor, moisture content and bulk density. The information provided in this study will be useful in developing an effective RF heating strategy to pasteurize dried vegetable powder.

Technical Abstract: Recently, Salmonella contamination was identified in low-moisture foods including dried vegetable powder. Radio Frequency (RF) dielectric heating is a potential alternative pasteurization method with short heating time. Dielectric properties of broccoli powder with 6.9, 9.1, 12.2, and 14.9%, w. b., moisture content were determined with a precision LCR meter and test fixture over temperatures ranging from 20 degree C to 80 degree C, at frequencies between 1 and 30 MHz. The RF heating rate in the broccoli powder was determined by using a 27.12-MHz, 6-kW RF oven. The results showed that dielectric properties, namely, the dielectric constant, e', and loss factor, e'', of broccoli powder were influenced by frequency, and moisture content and temperature of the sample. Both the dielectric constant and loss fractor increased with increasing moisture content and temperature, but decreased with increasing frequency. The relationship between moisture content, temperature and dielectric properties of broccoli powder at 13.56 and 27.12 MHz can be described by quadratic models with high correlation coefficients (R2 > 0.96). The RF heating rate increased linearly with dielectric loss factor, moisture content and bulk density. The information provided in this study is useful in developing an effective RF heating strategy to pasteurize dried vegetable powder.