1. Food Quality Laboratory, Agricultural Research ServiceU.S. Dept. of Agriculture Beltsville MD 20705 U.S.A
2. Environmental Microbiology and Food Safety Laboratory, Agricultural Research ServiceU.S. Dept. of Agriculture Beltsville MD 20705 U.S.A
3. Dept. of Nutrition and Food ScienceUniv. of Maryland College Park MD 20740 U.S.A.
4. Center for Food Safety and Security SystemsUniv. of Maryland College Park MD 20742 U.S.A.