Helpful Bacteria Keep Veggies Fresher

RALEIGH, N.C., Sept. 11--Today's consumers prefer preservative-free produce, but also demand the convenience of foods like salad-in-a-bag. A researcher with the U.S. Department of Agriculture says certain types of non-pathogenic bacteria could help give the public what they want plus an extra margin of safety.

Preservatives are there for a reason--to keep your food free of microorganisms that can cause spoilage or sickness by bacteria such as Listeria and E. coli that can cause spoilage or sickness, said microbiologist Fred Breidt with USDA's Agricultural Research Service. Some of these microorganisms thrive in airtight containers, so any natural alternative to synthetic preservatives would have to work under that condition, too.

A possible solution is lactic acid bacteria, called LAB by researchers. Present in certain types of pickles, yogurt and cheese, LAB produce natural acids that prevent Listeria from getting a foothold in foods. The extra margin of safety is that the same conditions that promote the growth of bad bacteria also cause LAB to thrive.

Lactic acid bacteria make an effective firewall, Breidt said. Say your refrigerator didn't maintain the proper temperature. That would be a great opportunity for Listeria, except the LAB would also be growing, stopping it cold.

Breidt said computer modeling will help guide his researchon using LAB to make fresh-packed vegetables and fruits--whether in bags or jars--convenient, natural and safe. He has designed a software program that shows how Listeria and LAB compete in a food sample. The program is built around the concept that for a given set of conditions, acid production will be the limiting factor for growth of disease-causing microorganisms.

Scientific contact: Fred Breidt, Food Science Research, ARS, USDA, Raleigh, N.C. 27695; phone (919) 515-2979, fax (919) 515-7124.