Development of a process for detecting nonthermal effects of microwave energy on microorganisms at low temperature

We developed an experimental process capable of isolating thermal and nonth ermal effects of microwave energy relative to the destruction of microorgan isms at low temperature. The concept combines instantaneous energy input to the food system by microwaves with rapid removal of thermal energy. The pr ocess used a double tube heat exchanger inside a continuous microwave dryer . The outer tube was transparent to microwaves, whereas the inner tube was stainless steel and was used for cooling the system. The microwave energy, 5-6 kW power, was absorbed by the process fluid in the annulus. The cooling water flowing in the inner tube removed the thermal energy from the proces s fluid to control temperature at or below 45C. The process was at turbulen t flow to assure a uniform temperature and dwell time. There were no detect ed nonthermal effects fi om microwave energy for yeast, Pediococcus sp., Es cherichia coli, Listeria innocua, or Enterobacter aerogenes in various test fluids, such as water, liquid egg, beer, apple juice, apple cider, and tom ato juice.