Ohmic sterilization inside a multi-layered laminate pouch for long-duration space missions

A pouch that can be used to ohmically reheat and sterilize food and later reused to stabilize waste will significantly reduce the Equivalent System Mass during a long term space mission. Reheating of food and stabilization of waste have been successfully done in the past using a V-shaped electrode pouch using pulsed ohmic heating, however improvement of field distribution was needed. The main goals of this work were to develop an improved pouch design to facilitate uniform ohmic heating of food; to model ohmic sterilization within the pouch; and to verify the model through an inoculated pack study.The pouch was redesigned to improve the electric potential distribution and hence heating uniformity. A temperature distribution study on a pouch with 227 g of tomato soup showed the presence of cold regions at the non-electrode sides due to channeling of current through a hotter and more conductive centre. A much more uniform temperature distribution was obtained the use of two external strip heaters installed along these sides. The ohmic heating process inside the pouch was simulated in 3D to predict possible cold and hot spots. The simulated heating profile was in good agreement with the measured values confirming the efficacy of the model. An inoculated pack study using Geobacillus stearothermophilus spores (ATCC 5973) confirmed the mathematical model. This technology provides a new method of sterilization inside sealed pouches/packets using ohmic heating.

► A rectangular-shaped ohmic heating pouch has been developed for Mars missions.
► Food may be ohmically heated within the pouch to a more or less uniform final process temperature.
► A mathematical model has been developed for the process, and verified.
► The concept may be used for future earth-based sterilization.