30D-6 |
Modeling the dielectric properties of vegetables and fruits as a function of temperature and composition |
O. SIPAHIOGLU, Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Rd., Columbus, OH 43210 and S. A. Barringer. Predictive equations modeling dielectric properties at sterilization temperatures are necessary to determine heating patterns during industrial microwave processing and reheating of RTE microwaveable foods. Thus, temperature dependence of dielectric properties of vegetables and fruits that are commonly thermally processed should be investigated. The objective of this study was to generate predictive equations for the dielectric properties of vegetables and fruits at 5-130°C as a function of temperature, moisture, ash content and water activity. The dielectric properties of individual vegetables and fruits were also modeled separately as a function of temperature. Vegetables included carrot, parsley, spinach, radish, turnip, yam, potato, garlic, parsnip, and broccoli. Fruits included cucumber, apple, pear, banana, and corn. The dielectric properties of the samples were measured at 2450MHz using an open ended coaxial probe and a network analyzer. Water activity was determined using Aqualab aw analyzer, moisture and ash content by vacuum and ashing ovens. Multiple regression equations were generated using JMPin software. The dielectric properties of vegetables and fruits can be modeled by: k′=38.6–0.126•T–0.455•M-14.5•A–0.004•M•T+0.0733•A•T R2adj=0.72 k′′=7.72–0.452•T+0.00138•T2–0.0745•M+22.9•A–13.4•A2 +0.00221•M•T+ 0.151•A•T R2adj=0.74 The dielectric properties of vegetables can be modeled by: k′=–244+1.34•T+4.59•M–427•A+377•A2–0.0142•M•T–0.315•A•T R2adj=0.86 k′′=–100–0.161•T+0.00142•T2+2.43•M–379•A+316•A2 R2adj=0.86 The dielectric properties of fruits can be modeled by: k′=22.1+0.238•T+0.553•M–0.000513•T2–0.00387•M•T R2adj=0.83 k′′=33.4–0.442•T+0.00140•T2–0.175•M+1.44•A+ 0.00158•M•T+ 0.229•A•T R2adj=0.89 Dielectric constant of the samples decreased with temperature and increased with moisture. Dielectric loss factor first decreased then increased with temperature. The inflection point was dependent on the ash content. As ash content decreased, the inflection point occurred at higher temperatures. Water activity and moisture content worked equally well in the equations. The predictive equations can be used for determining temperature profiles during microwave heating.
Session 30D, Food Engineering: Physical and chemical properties
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