Irradiation, chlorine combine to enhance safety, shelf life of produce.

Nonthermal processing techniques such as irradiation have the potential to improve safety without reducing the fresh-like qualities of minimally processed vegetables. Optimization, using combination processing, can also result in enhancing product shelf life.

Researchers at Chapman University examined the effects of irradiation on the microbial and sensory attributes of various fresh-cut products. Using a protocol designed to recover injured cells, the survival of E. coli O157:H7 was evaluated in shredded iceberg lettuce and cilantro that had been inoculated with a six-strain cocktail of E. coli O157:H7, chlorinated at 200 mg per mL and irradiated at 0.5 kGy. Chlorination combined with irradiation produced more than a 4.5 log reduction in E. coli O157:H7 levels for both cilantro and lettuce. Irradiation at this level did not cause any softening or wilting of the product. Sensory attributes were not adversely affected for either product.

In addition, diced Roma tomatoes and diced bell peppers were irradiated at several low levels. Investigators evaluated these products for changes in their microbial, physical, chemical and sensory properties. The total plate counts, yeast and molds were significantly reduced in the irradiated samples. At dose levels greater than 1 kGy, a loss of firmness limited the acceptability of the product. However, at low-dose levels, the change was not detectable by a nine-member trained sensory panel.

A six-log reduction in L. monocytogenes inoculated into refrigerated avocado pulp was observed following irradiation at 3 kGy. No significant reduction was observed at 1 kGy. Adjusting the pH to as low as 4.5 did not inhibit Listeria survival in avocado pulp and did not enhance irradiation sensitivity. Although the activity of polyphenoloxidase was slightly enhanced, there was no perceptible change in the product's rate of browning. Other sensory attributes, such as flavor and odor, were not affected by irradiation.

Scientists at Chapman have been investigating low-dose irradiation on ready-to-eat products such as fresh-cut produce, ready meals and deli salads. As you know, irradiation is approved for fruits and vegetables to inhibit sprouting and accomplish insect disinfestation up to a dose of 1 kGy. Meat and poultry can be irradiated at a higher dose for the purpose of enhancing safety.

A petition is currently under consideration at the FDA that would allow ready-to-eat products to be irradiated to enhance their safety. Right now this is not approved in the United States. Chapman scientists have been approached by numerous companies interested in testing their products--usually in anticipation of approval of the petition. The university researchers are open to additional industrial collaborations. Further information. Denise Foley, Department of Biological Sciences, Chapman University, 1 University Dr., Orange, CA 92866; phone: [phone]; fax: [phone]; email: [e-mail].