title: Determination of the Thermal Inactivation Kinetics of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 and non-O157 in Buffer and a Spinach Homogenate.
abstract: Produce has been associated with a rising number of foodborne illness outbreaks. While much produce is consumed raw, some is treated with mild heat, such as blanching or cooking. The objectives of this research were to compare the thermal inactivation kinetics of Listeria monocytogenes, Salmonella enterica, Shiga toxin-producing Escherichia coli (STEC) O157:H7, and non-O157 STEC in phosphate-buffered saline (PBS; pH 7.2) and a spinach homogenate and to provide an estimate of the safety of mild heat processes for spinach. Five individual strains of S. enterica, L. monocytogenes, STEC O157:H7, and non-O157 STEC were tested in PBS in 2-ml glass vials, and cocktails of the organisms were tested in blended spinach in vacuum-sealed bags. For Listeria and Salmonella at 56 to 60°C, D-values in PBS ranged from 4.42 ± 0.94 to 0.35 ± 0.03 min and 2.11 ± 0.14 to 0.16 ± 0.03 min, respectively. D-values at 54 to 58°C were 5.18 ± 0.21 to 0.53 ± 0.04 min for STEC O157:H7 and 5.01 ± 0.60 to 0.60 ± 0.13 min for non-O157 STEC. In spinach at 56 to 60°C, Listeria D-values were 11.77 ± 2.18 to 1.22 ± 0.12 min and Salmonella D-values were 3.51 ± 0.06 to 0.47 ± 0.06 min. D-values for STEC O157:H7 and non-O157 STEC were 7.21 ± 0.17 to 1.07 ± 0.11 min and 5.57 ± 0.38 to 0.99 ± 0.07 min, respectively, at 56 to 60°C. In spinach, z-values were 4.07 ± 0.16, 4.59 ± 0.26, 4.80 ± 0.92, and 5.22 ± 0.20°C for Listeria, Salmonella, STEC O157:H7, and non-O157 STEC, respectively. Results indicated that a mild thermal treatment of blended spinach at 70°C for less than 1 min would result in a 6-log reduction of all pathogens tested. These findings may assist the food industry in the design of suitable mild thermal processes to ensure food safety.
authors.affiliation: Department of Food Science and Technology, University of Tennessee-Knoxville, 2600 River Drive, Knoxville, Tennessee 37996-4591, USA; Department of Poultry Science, Auburn University, 260 Lem Morrison Drive, Auburn, AL 36849, USA.
authors.forename: Emefa Angelica
authors.initials: EA
authors.lastname: Monu
authors.affiliation: Department of Food Science and Technology, University of Tennessee-Knoxville, 2600 River Drive, Knoxville, Tennessee 37996-4591, USA.
authors.forename: Malcond
authors.initials: M
authors.lastname: Valladares
authors.affiliation: Department of Food Science and Technology, University of Tennessee-Knoxville, 2600 River Drive, Knoxville, Tennessee 37996-4591, USA.
authors.forename: Doris H
authors.initials: DH
authors.lastname: D'Souza
authors.affiliation: Department of Food Science and Technology, University of Tennessee-Knoxville, 2600 River Drive, Knoxville, Tennessee 37996-4591, USA. pmdavidson@utk.edu.
authors.forename: P Michael
authors.initials: PM
authors.lastname: Davidson
mesh_terms: D004926:Escherichia coli / Q000502:physiology*; D019453:Escherichia coli O157 / Q000502:physiology*; D005516:Food Microbiology; D059022:Food Safety; D006358:Hot Temperature; D007700:Kinetics; D008089:Listeria monocytogenes / Q000502:physiology*; D012475:Salmonella; D019779:Salmonella enterica / Q000502:physiology*; D018724:Spinacia oleracea / Q000382:microbiology*