Remote plasma reactor reduces pathogen levels on fresh produce.

Safety is a major concern in every sector of the food industry. Scientists continue to evaluate innovative ways to inhibit or destroy pathogenic microorganisms in products.

The traditional methods of inactivating or killing pathogens in foods have involved thermal processes. Now, the increase in demand for fresh or minimally processed fruits and vegetables has motivated research aimed at developing novel, nonthermal techniques for reducing microbial populations without sacrificing the quality of the product.

Neutral particles, electrons and positively or negatively charged atoms and molecules comprise plasma, the fourth state of matter. When a gas passes through plasma, the gas becomes excited, ionized or dissociated by electron or ion collisions with the background gas. This leads to the formation of active species, such as atomic oxygen, ozone, and free radicals--hydroxyl, superoxide and nitrogen oxides. These reactive species have antimicrobial activity.

Using the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP[R]) system developed at the University of Tennessee, researchers at the university have shown that it is possible to inactivate E. coli O157:H7, Salmonella and L. monocytogenes on apples, cantaloupe and lettuce, respectively. This process could serve as a novel, non-thermal technology for reducing microbial populations on produce surfaces. The system electrically breaks down air at standard pressure and ambient temperatures, creating highly reactive chemical species with antimicrobial activity.

In experiments, samples were exposed inside a chamber affixed to the plasma's blower unit. This configuration makes it possible to place the sample outside of the plasma generation unit while allowing airflow to carry the antimicrobial active species.

The process reduced E. coli O157:H7 populations by more than 1 log after treatment lasting up to 1 minute, and by more than 2 logs after a 2-minute exposure. Salmonella populations declined by more than 2 logs after a 1-minute treatment. Three- and 5-minute exposure times resulted in a greater than 3-log reduction. L. monocytogenes populations declined by 1 log after a 1-minute exposure. Three- and 5-minute exposure times resulted in greater than 3-and 5-log reductions, respectively.

Further information. Faith Critzer, Experiment Station, Department of Food Science and Technology, University of Tennessee, 100 Food Safety and Processing Building, 2605 River Dr., Knoxville, TN 37996; phone: [phone]; email:[e-mail].