30D-4 |
Effect of plant parts and temperature on dielectric properties of broccoli |
N. GUNASEKARAN and P. Mallikarjunan. Biological Systems Engineering, Virginia Polytechnic Institute and State University, 200 Seitz Hall, Blacksburg, VA 24061 Dielectric properties of a food material play a major role in determining the interaction between food and electromagnetic energy. Microwave heating is widely used for cooking or thawing frozen broccoli. Studies showed that plant parts significantly affect temperature profile. Very few attempts were made to measure dielectric properties of broccoli. The objective of this study is to determine the dielectric properties of frozen broccoli (floret and stem) in 0.3 GHz to 3 GHz frequency range at temperatures from -25°C to 75°C. Frozen broccoli was obtained from local grocery store. Ethylene glycol was used in a constant temperature bath as the medium to maintain experimental temperatures. The covered sample was immersed in ethylene glycol until reaching the desired temperature. The dielectric properties were determined by measurements on an open-ended, coaxial line with copper conductors, connected to a Network analyzer. Dielectric Probe Kit software was used to calculate the dielectric properties. Moisture content of floret and stem were determined. Results of this experiment showed that the dielectric constant decreased from 83 to 66 with increase in temperature from 1 to 75°C at 915MHz for stems. It varied from 4 to 15 at -25 to 1°C. Similar trend was observed at 2415MHz but lesser values. The dielectric loss factor varied from 18 to 26 in temperatures between 1 and 75°C at 915MHz for stems. It varied from 0.4 to 3 at -25 to 1°C. At 2450MHz, loss factor was 2.5 to 6 in frozen temperature range. It showed the highest value, 20 at 1°C and reached 16 at 75°C for stems. The dielectric constant and the dielectric loss factor of florets were lower than that of stems. Results of this research will be highly helpful in developing microwave-heating procedures that will increase microbial safety, and in developing proper thawing procedure.
Session 30D, Food Engineering: Physical and chemical properties
|