Sterilization and pasteurization of foods using radio frequency heating

A pilot-scale radio frequency (RF) heating system using a parallel-plate pressure vessel was developed for use in developing sterilization and pasteurization processes for packaged foods. A water conditioning system was used to immerse the package in water, which greatly increased heating uniformity. Overpressure was used to suppress boiling within the vessel and to ensure package integrity.; In support of this project, a dielectric properties measurement system was used to characterize the complex permittivity of materials used in dielectric heating over a range of temperatures and frequencies. A temperature-controlled test fixture was developed that permitted the material under test (MUT) to be heated and cooled at temperatures spanning 0° to 130°C. Dielectric measurements were performed using an impedance analyzer and a network analyzer with an open-ended coaxial probe at frequencies extending from 1 MHz to 3 GHz, which includes all commonly used dielectric heating frequencies. The dielectric property information was used to develop an optimal balance of physical properties between a packaged food product and the processing liquid used to immerse the container during treatment, which is required to achieve rapid, uniform heat treatment of the product.; A computer simulation of the system was performed using the Finite-Difference Time-Domain method and the measured dielectric data, the predicted results were compared with those obtained experimentally.; The results of this work show that RF heating may be used as an alternative to traditional steam retort heating in the sterilization of packaged military rations. RF heating may provide more rapid heating at the core, typically the most difficult region to sterilize in any food package. In doing so, RF heating may provide improved heating uniformity, which would reduce localized overcooking present in most heat-treated foods. This could serve to protect the flavor, texture, and nutrition of the packaged food by lowering the overall heating time.