Sterilization solutions for aseptic processing using a continuous flow microwave system

Abstract

The conventional method of sterilization of an aseptic processing system by recirculating hot water cannot be applied to a continuous flow microwave heating system. Therefore, a model solution with dielectric and flow properties similar to that of the food product is required as a sterilization solution. Dielectric properties of solutions of table salt, sugar, CMC, and mixtures of these solutes were measured and correlations for the dependence of dielectric properties on concentration of solute and temperature were developed. Sterilization solutions were prepared by matching the dielectric and rheological properties of solutions prepared from table salt, sugar, and CMC to those of the food product to be processed. Dielectric properties of milk and sweet potato puree were compared to those of salt–sugar–CMC mixtures and a model solution that closely matched the properties of each product was prepared and experimentally tested in a 5 kW continuous flow microwave system operating at 915 MHz. The temperature profile at the exit of the heating section during heating of the sterilization solution was compared to the temperature profile during heating of the product. It was observed that the temperatures during transition from sterilization solution to the product did not change appreciably. Thus, these model solutions can be used as sterilization solutions for aseptic processing using a continuous flow microwave system.