Increased microbial risks may offset benefits of extended shelf life.

A worldwide market for fresh produce has resulted in a need for increased shipping time and longer retail display time. A number of forces have been driving this trend, including consumer demand for minimally processed, convenient products. Modified atmosphere packaging (MAP) is one approach to increasing shelf life of whole and minimally processed produce, including prepared salads, precut vegetables and peeled or sliced fruits. But you should be aware of both the positive and negative consequences of MAP. While MAP has been used to increase the life of produce, some don't realize how MAP affects the growth of pathogenic microorganisms in many products.

Investigators at Cornell University (Department of Food Science, Stocking Hall, Ithaca, NY 14853) are investigating the potential that exists for the growth of pathogenic bacteria in MAP extended-shelf-life products. Extending the shelf life of refrigerated products could increase the potential for microbial growth in several ways. Increasing the time during which food remains edible increases the time in which even slow-developing pathogens grow to significant numbers or produce toxin. MAP can retard the development of spoilage organisms, which warn consumers about the age and condition of a product. Also, placing produce that respires in modified atmospheres might change the atmosphere and stimulate pathogen growth.

What's of key importance is the relationship between the pathogenic microorganism growth rate and a food's decay rate. Produce that's spoiled beyond being edible is of little concern, unlike produce that remains edible thanks to MAP, but which could be infectious or toxic. Researchers have found there is a greater prevalence of L. monocytogenes in prepared salads most likely to be packaged in MAP. The bacteria will grow to high numbers in lettuce, cabbage and a variety of vegetables over time. Cornell scientists indicate that problems not usually encountered with fresh produce could occur if shelf life is extended without action taken to stop microbial growth.

MAP is particularly vulnerable when it comes to product safety because the technology may inhibit aerobic microorganisms, which often warn about spoilage, while pathogenic bacteria grow. Additional research is needed into the microbial safety of MAP and other techniques aimed at extending shelf life. Microbial interactions, the effect of MAP on psychrotrophic pathogens, and the effects of package failure and temperature abuse should be studied.

Further information. Joseph Hotchkiss; phone: [phone]; fax: [phone].