A simple switch in cattle diets—from corn to hay—for the last five days before slaughter could reduce the risk of E. coli infection in humans, new research suggests. E. coli causes about 20,000 infections of people and 200 deaths a year in the United states. ARS and Cornell University scientists conducted preliminary studies with 61 head of beef cattle. The scientists found that cattle fed corn grain tended to develop heartier, acid-resistant strains of E. coli in their digestive tracts. Acid resistance facilitates the passage of bacteria through the gastric stomach and allows them to colonize the human colon. Switching to hay just before slaughter reduced the occurrence of these strains. Most E. coli strains occur naturally in cattle, are harmless and do not harm people. But some strains are very dangerous, especially E. coli 0157:H7. It can cause bloody diarrhea, kidney failure and death in humans. Meat can be contaminated with the bacteria if it comes in contact with feces at slaughter. The new research reveals a previously unknown mechanism that enables the bacteria to develop acid resistance. Some undigested grain ferments in the animal's colon, producing volatile fatty acids. E. coli bacteria, including the 0157:H7 strain, develop genetic defenses that help them thrive in this low-pH environment. But cattle digest hay easily; as a result, acid levels in the colon remain low, discouraging the development of acid-resistant bacteria. More comprehensive evaluations using larger numbers of animals are planned. The team also plans to test other grains in addition to corn.
U.S. Plant, Soil and Nutrition Research, Ithaca, NY
James B. Russell, (607) 255-4508, jbr8@correll.edu

Campbell's Soup and Beech-Nut are using an ARS-developed technique to screen fruits and vegetables for pesticides before buying them. The companies take samples of the produce to their laboratories where they use an automated technique that can spot any of more than 50 major pesticides in several classes, such as the insecticides chloropyrifos and permethrin, an organophosphate and pyrethroid, resepectively. The method was developed by an ARS chemist for commercial use and use by regulatory labs. The North Carolina Department of Food and Agriculture has adopted the technique, which is an automated use of supercritical fluid extraction, a method used to safely decaffeinate coffee, for example. It eliminates almost all use of liquid solvents for the analysis. The technique saves time and money as well as being more accurate than standard techniques: 85 to 100 percent, depending on the pesticide. And it can detect some pesticides that are missed by standard techniques. The method was developed on grapes, carrots, potatoes and broccoli. The fruits and vegetables are shredded and mixed in a food processor to prepare samples. Analysis of the samples compared favorably with results from seven laboratories using traditional detectors and solvent-based extraction procedures.
Environmental Chemistry Laboratory, Beltsville, MD
Steven J. Lehotay, (301) 504-6511, slehotay@asrr.arsusda.gov

A new simple, inexpensive test accurately detects E. coli 0157 in food products. An ARS scientist developed the test from equipment and technology patented by IGEN International, Inc., of Gaithersburg, MD. Antibodies—molecules custom-tailored to bind to a specific substance—are key to the test, which uses magnetic beads coated with an E. coli 0157 antibody and a ruthenium-labeled antibody. Ruthenium is a metal that, through an electrochemical reaction, emits light that helps detect E. coli. The new test works on hamburger meat and is 10 to 100 times more sensitive than other E. coli tests. No special training is necessary. The equipment, including a computer, fits on a small table. About 50 samples per hour can be tested. They're loaded onto a tray similar to the carousel of a slide projector. Total time from sample to answer: only 6 to 8 hours. Several large commercial meat suppliers are evaluating the test. From the new assay, IGEN hopes to develop a line of fast, highly sensitive tests that will help food producers detect contaminants.
Eastern Regional Research Center, Wyndmoor, PA
C. Gerald Crawford, (215) 233-6628, cgcrawford@arserrc.gov

Routine pasteurization safeguards milk from an organism known to cause a cattle disease—and suspected by British researchers to be linked with Crohn's disease in people. High-temperature, short-time pasteurization (HTST) is routinely performed on commercial Grade A milk. ARS researchers determined that HTST kills Mycobacterium paratuberculosis, the organism that causes Johne's disease in cattle. M. paratuberculosis is shed in low quantities in the milk of some Johne's-infected cows, so ARS researchers conducted the pasteurization studies—simulating industry conditions—after a 1994 British scientific report. The British researchers suggested that the Johne's organism might cause Crohn's disease, a severe intestinal disease in humans. In the laboratory, ARS researchers inoculated raw, unpasteurized milk with two strains of the bacterium: one from an infected cow and the other from a Crohn's patient. The milk was held at 162 ^oF for 15 seconds. When milk samples were re-checked 6 months later, scientists again found no evidence of M. paratuberculosis. Despite this organism's name, it has no connection to tuberculosis in either cattle or humans.
National Animal Disease Center, Ames, IA
Judith R. Stabel, (515) 239-8325, jstabel@nadc.ars.usda.gov

Now, cut-up honeydew melons stay fresh and marketable 2 days longer—a 20 percent improvement—thanks to new procedures for controlled atmosphere (CA) storage worked out by ARS scientists. Treated melon sections also have less microbial growth than the control samples. Honeydew cubes prepared at the supermarket typically have a sale date of only 2 or 3 days after they're cut. An ARS food technologist subjected cut-up honeydews to a CA of 2 percent oxygen and 10 percent carbon dioxide at 41 ^oF for 9 days. The control sample was stored in air. On day 5, melon cubes in CA had less bacterial growth and stronger honeydew aroma than the controls. On day 6, CA-stored samples were still moist, with good green color, aroma, taste and sweetness that lasted through day 9. Control samples had microbial growth and an offensive odor by day 9. This research also showed that with controlled atmosphere storage, maintaining the packaged, cut-up honeydews at 41 ^oF at all times is crucial.
Horticultural Crops Quality Laboratory, Beltsville, MD
Alley E. Watada, (301) 504-5107, awatada@asrr.arsusda.gov

A new way to chemically change vegetable oils produces solid margarines with lower levels of trans fatty acids than the conventional method of hydrogenation. That's good health news for consumers, because studies have shown that trans fatty acids can raise cholesterol levels in some people. Hydrogenation involves heating a fat mixture under high heat and pressure to chemically add hydrogen. But that results in high levels of trans fatty acids—between 10 and 30 percent. In the new process called low-trans hydrogenation, scientists changed some parameters of hydrogenation. The result was oil with a chemical structure that allows scientists to make margarine with less than 8 percent trans fatty acids. ARS scientists are working to further develop that technology for commercial food applications.
Food Quality and Safety Research Laboratory, Peoria, IL
Gary R. List, (309) 681-6388, listgr@mail.ncaur.usda.gov

Two wheat genes now being scrutinized by ARS researchers in California might increase the use of starch made from wheat flour. The genes direct wheat to make enzymes that, in turn, are used to make molecules called amylopectins. With the genes, researchers might soon to be able to increase the amount of amylopectin molecules and decrease the quantity of another kind of starch molecule known as amylose. That may result in value-added, low-amylose flour—the kind used for noodle-making because it improves texture. Reduced-amylose flour may also improve doughs for frozen foods like pizza crusts or ready-to-bake breads by helping maintain flavors. Other researchers had already found similar starch genes in corn, but the ARS team was among the first to find counterpart genes in wheat.
Western Regional Research Center, Albany, CA
Kent F. McCue, (510) 559-5796, kmccue@pw.usda.gov

Last Updated: November 13, 1998
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