1. Department of Food Science and Technology, The University of Tennessee, 2509 River Drive, Knoxville, Tennessee 37996; Food Safety Center of Excellence, The University of Tennessee, 2605 River Drive, Knoxville, Tennessee 37996; Produce Quality and Safety Laboratory, Agricultural Research Service, U.S. Departnent of Agriculture, 10300 Baltimore Avenue, Beltsville, Maryland 20705; and Department of Plant Sciences, The University of Tennessee, 2431 Joe Johnson Drive, Knoxville, Tennessee 37996