TY - JOUR
T1 - The effects of growth temperature and growth phase on the inactivation of Listeria monocytogenes in whole milk subject to high pressure processing
AU - Hayman, Melinda M.
AU - Anantheswaran, Ramaswamy C.
AU - Knabel, Stephen J.
N1 - Funding Information:
We appreciate the assistance of Michael Kalaras and Lena Le for media preparation and assisting in some of the experiments. We would also like to thank Lanyu Mi from the PSU Statistical Consulting Center for her recommendations. This work was funded by a USDA Milk Safety Grant to the Pennsylvania State University.
PY - 2007/4/30
Y1 - 2007/4/30
N2 - The aim of this study was to explore the effect of a wide range of growth temperatures, growth phases and plating media on the inactivation of Listeria monocytogenes by high pressure processing (HPP). In part one, L. monocytogenes was grown to mid-stationary phase at 4, 15, 25, 35 or 43 °C, inoculated into whole UHT milk at ∼ 107 CFU/ml and high pressure processed at 400 MPa at room temperature (20-25 °C). Afterward, the HPP milk was plated on Tryptic Soy Yeast Extract Agar (TSYEA) and Modified Oxford Agar (MOX) to determine the degree of injury. For part two, cells were grown to mid-exponential, late-exponential or mid-stationary phase at 15 or 43 °C and processed in the same way. Time to reach a 5-log reduction was determined and data were analysed by ANOVA. The results from part one showed that both growth temperature and plating medium had a significant effect (P < 0.001) on the inactivation of stationary phase L. monocytogenes by HPP. Tukey's pairwise comparisons revealed that the effects of all temperatures, except 35 and 43 °C, were significantly different (P < 0.05). Cells grown at 15 °C were most sensitive to HPP, followed by cells grown at 4, 25 or 35 °C, with cells grown at 43 °C appearing to be the most resistant. Inactivation of cells grown at 4, 15 or 25 °C followed first order kinetics, whereas cells grown at 35 or 43 °C displayed non-linear inactivation kinetics due to tailing. In part two, both growth phase and plating medium had significant effects on the inactivation (P ≤ 0.001) of L. monocytogenes by HPP. Cells grown at 15 °C to mid-stationary phase were the most pressure-resistant when tested on both media, and were significantly more resistant (P < 0.05) than cells grown at the same temperature to the other two phases of growth. There was no significant difference between mid- and late-exponential phase cells grown at 15 °C. When cells were grown at 43 °C, mid-exponential phase cells were significantly more sensitive (P < 0.05) than either late-exponential or mid-stationary phase cells, with no difference between late-exponential or mid-stationary phase cells. It was postulated that membrane composition, stationary phase proteins and/or stress proteins may affect pressure resistance.
AB - The aim of this study was to explore the effect of a wide range of growth temperatures, growth phases and plating media on the inactivation of Listeria monocytogenes by high pressure processing (HPP). In part one, L. monocytogenes was grown to mid-stationary phase at 4, 15, 25, 35 or 43 °C, inoculated into whole UHT milk at ∼ 107 CFU/ml and high pressure processed at 400 MPa at room temperature (20-25 °C). Afterward, the HPP milk was plated on Tryptic Soy Yeast Extract Agar (TSYEA) and Modified Oxford Agar (MOX) to determine the degree of injury. For part two, cells were grown to mid-exponential, late-exponential or mid-stationary phase at 15 or 43 °C and processed in the same way. Time to reach a 5-log reduction was determined and data were analysed by ANOVA. The results from part one showed that both growth temperature and plating medium had a significant effect (P < 0.001) on the inactivation of stationary phase L. monocytogenes by HPP. Tukey's pairwise comparisons revealed that the effects of all temperatures, except 35 and 43 °C, were significantly different (P < 0.05). Cells grown at 15 °C were most sensitive to HPP, followed by cells grown at 4, 25 or 35 °C, with cells grown at 43 °C appearing to be the most resistant. Inactivation of cells grown at 4, 15 or 25 °C followed first order kinetics, whereas cells grown at 35 or 43 °C displayed non-linear inactivation kinetics due to tailing. In part two, both growth phase and plating medium had significant effects on the inactivation (P ≤ 0.001) of L. monocytogenes by HPP. Cells grown at 15 °C to mid-stationary phase were the most pressure-resistant when tested on both media, and were significantly more resistant (P < 0.05) than cells grown at the same temperature to the other two phases of growth. There was no significant difference between mid- and late-exponential phase cells grown at 15 °C. When cells were grown at 43 °C, mid-exponential phase cells were significantly more sensitive (P < 0.05) than either late-exponential or mid-stationary phase cells, with no difference between late-exponential or mid-stationary phase cells. It was postulated that membrane composition, stationary phase proteins and/or stress proteins may affect pressure resistance.
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U2 - 10.1016/j.ijfoodmicro.2006.10.019
DO - 10.1016/j.ijfoodmicro.2006.10.019
M3 - Article
C2 - 17173999
AN - SCOPUS:33847623757
SN - 0168-1605
VL - 115
SP - 220
EP - 226
JO - International journal of food microbiology
JF - International journal of food microbiology
IS - 2
ER -