By combining gentle bactericidal and bacteriostatic technologies, a greater overall effect on the microbial load of the product may be achieved when compared to a single extreme treatment that could negatively affect fragile plant tissue, altering texture, flavor, and shelf life. Refrigeration is not a good defense against psychrophillic microorganisms such as Listeria and Yersinia entercolitica which have the potential to cause food-borne illness. While chlorine can have a substantial lethal effect on surface microorganisms, its effectiveness is limited by its inability to reach into tissue crevices and its rapid inactivation from contact with organic matter in the wash water. Heat treatment is generally not used because it disrupts the fresh-like character. Modified atmosphere packaging has been used to preserve the sensory quality and to limit microbial growth, however the hazard from certain microorganisms such as Listeria monocytogenes and Aeromonas hydrophila may be increased.
Irradiation is an established process with clearly documented safety and efficacy.
Its efficacy stems from the fact that it does not increase the temperature of the product, it can be used post packaging, and its activity is not limited to the surface. A long held belief is that vegetable tissues are susceptible to damage by irradiation, even at low levels of irradiation. Another belief is that irradiation at levels which do not cause tissue damage may be ineffective against pathogenic or spoilage microorganisms. While some vegetables, especially leafy vegetables, are irradiation sensitive, lack of research on minimally processed commodities does not allow comment on the effects of low dose irradiation on tissue damage or inhibition of microbial decay especially at low doses. In the three years since irradiation work was initiated at Chapman University we have evaluated diced celery, cut romaine lettuce, shredded iceberg lettuce, diced tomatoes, diced bell peppers, and orange juice.