Non-thermal Fresh Food Sanitation By Atmospheric Pressure Plasma

The Non-Thermal Sanitation by Atmospheric Pressure Plasma (NTSAPP) system was developed for sanitizing fresh food on long-duration space missions. Plasmas are ionized gases generated by electrical discharges and composed of electrons, positive/negative ions, neutrons, and other neutral species. One of the most important properties of plasmas is the very high energy that they have, about 3-4 eV, in typical laboratory cold plasmas. Plasma processes are known to be highly effective in promoting oxidation, enhancing molecular dissociation, and producing free radicals and other types of high energies. Non-thermal plasmas provide an effective way to generate extremely reactive species and initiate a variety of chemical reactions of use in surface sanitation of fresh fruit and vegetables. The system operates by passing a carrier gas through plasma jet reactors. The generated plasma then flows with the air through a rotating food sanitation chamber. After passing around the material to be sanitized the carrier gas flows through a scrubber to break down any harmful components prior to being returned to the environment. The system is capable of sanitizing fresh fruits and vegetables in minutes, with minimal consumables and byproducts. The antimicrobial efficacy of an integrated system prototype was tested with several process gases, food items, and microbes. Testing showed that performance with bottled gas mixtures was not significantly better than performance with lab air as the process gas, which has the benefit of operation without pressurized gas lines and with minimal consumables. Tests performed with samples of lettuce, tomato, and radish inoculated with E. coli and Salmonella showed that fifteen minutes of sanitizing resulted in a 3.7 log reduction of E. coli on lettuce and tomato, a 3.2 log reduction of E. coli on radish, a 3.6 log reduction of Salmonella on lettuce and tomato and a 3 log reduction of Salmonellaon radish. Testing with trained sensory analysis panelists showed the process had no significant impact on taste, olfactory or appearance quality.  An alternative configuration using a flat tray system is being developed for commercial applications.