Helpful Bacteria Keep Veggies
By Jill Lee
September 11, 1996
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,
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
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,
Research, ARS, USDA, Raleigh, N.C. 27695; phone (919) 515-2979, fax (919)