A System for Continuous Thermal Processing of Food Pouches Using Microwave Energy

Abstract

— A system for continuous microwave sterilization of foods packaged in plastic pouches has been designed, constructed and tested. Air pressure was used to prevent pouch rupture. Pouches containing food for use in military rations were sealed and introduced through an air lock on to a conveyor inside a plastic pipe within a microwave cavity. Microwave energy was supplied up to 10 kw at 2,450 MHz. Conveyor speed and power were regulated to provide the process time and temperature. Cooling was achieved in a cooling bath. Pouches were overpackaged in a foil laminate for additional protection. Several food products were processed. Total process times of 9–14 min were achieved.

A review of microwaves for food processing

“…A practical problem in microwave sterilizing is the need to maintain the integrity of the flexible plastic pack; because temperatures in excess of 100°C are required the system must be pressurized, both for heating and cooling. Research continues, for example at the U.S. Army Natick Labs; they have built special pressurized microwave equipment to study the processing parameters involved in heating and cooling flexible packs of food (Kenyon et al, 1971 ;Ayoub et al, 1974).…”

Dielectric properties of egg whites and whole eggs as influenced by thermal treatments

“…During a conventional sterilization process, the surface of the packaged food is exposed to high temperature much longer than the inner part, resulting in overcooking of the food. Dielectric heating, including radio frequency (RF) and microwave heating, can potentially reduce processing time and improve heating uniformity because the heat is volumetrically generated inside the food by conversion of alternating electromagnetic (EM) energy to thermal energy (Cathcart, Parker, & Beattie, 1947;Kenyon, Westcott, Case, & Gould, 1971;Kinn, 1947). But engineering design of dielectric heating is hindered by a lack of information about the dielectric properties of selected foods as functions of food composition, temperature, and EM wave frequencies (Zhao, Flugstad, Kolbe, Park, & Wells, 2000).…”

Microwave heating to prevent deterioration of cottonseed during storage

“…Advances in microwave heating technology should make it possible to apply microwave heat to materials as they pass through a covered conveyor system (20). Since conveyor sysems are used in oilseed processing mills to transfer seed from trucks on arrival at the mill to storage houses or silos, the application of microwave heat seems to have potential.…”