Determining Thermal Death Kinetics of Listeria innocua in Apple Pulp

This report presents an experimental analysis of the thermal death kinetics of Listeria innocua, a bacterium often found in food environments. The study focuses on determining the parameters that successfully reduce the bacterial load to acceptable levels, specifically examining the effects of temperature on the bacterium's survival in apple pulp. The experiment involved determining Thermal Death Time (TDT), D-value, and Z-value through graphical methods. Results indicate that at 62°C, the lowest TDT was 71.58 minutes with a corresponding D-value of 8.51 minutes, and a Z-value of 13.57. The findings suggest a time and temperature-dependent inactivation of Listeria innocua, which is crucial for ensuring food safety and effective sterilization processes within the food industry. These results are essential for establishing effective protocols to eliminate the bacteria, thus preventing potential contamination and ensuring the safety of food products. This report provides valuable insights into the thermal inactivation of the bacteria, aiding in the development of improved food processing and packaging techniques.

MODULE 3
Presented by Soraya
Behnia

RESULTS AND
DISCUSSIONListeria innocua, is a hardy bacteria that has been found growing on diverse locations, be
it soil, food or animals. They are capable of surviving in a broader range of temperature and
pH conditions and are mostly harmless to humans. However, in recent times a few reports
of them causing bacteremia in immuno-compromised and aged individuals have been
reported.## [Fatal Case of Listeria innocua Bacteremia]
In the food and packaging industry, contamination with another species, Listeria
monocytogenes is considered extremely dangerous and hence unacceptable as it causes
listeriosis. However, this virulent strain is not able to survive the same extremes of
temperatures and pH as the Listeria innocua species. Hence, the presence or absence of
the non-pathogenic Listeria innocua is mostly used to determine whether the food is fit for
packaging or not. ##[ Prediction of Listeria innocua survival in fully cooked chicken
breast products during post package thermal treatment] , ##[Thermal Inactivation of

In this study, we performed an experiment to determine the thermal death kinetics of
the Listeria innocua strain from apple pulp. In order to define the conditions that
successfully reduce the bacterial load to acceptable levels we determined some
commonly used parameters such as TDT, D-value, and Z- value by the graphical method.
##[https://nptel.ac.in/courses/103107088/module16/lecture1/lecture1.pdf]
 Under the parameters and the variables of our study, we can conclude that within the
temperature range tested for TDT (58°C-62°C), 62°C showed the lowest TDT at 71.58
minutes. Also, the corresponding D–value was the best at 8.51 minutes. The z- value that
was determined from a plot of LogD vs Temperature, was 13.57. hence, we may
conclude that following this protocol of heating , a temperature and time dependent
kinning of the bacterium belonging to Listeria sp. Can be successfully achieved.

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55 56 57 58 59 60 61 62 63
0.0
1.0
2.0
3.0
f(x) = − 0.0737303660623493 x + 5.73655059298305
R² = 0.21903648616266
Temperature (°C)
log D
Graphical
method
Temperature D
value
Slope of
Regression Line
D value
(mins)
TDT (y=0)
mins
log
D
Z °C from
slope
56 D56 -0.0541 18.48 152.33 1.27 13.57
58 D58 -0.0124 80.65 681.95 1.91
60 D60 -0.0361 27.70 231.57 1.44
62 D62 -0.1175 8.51 71.58 0.93logD70 F = D70 * (logN0-
logN), s
Temperatu
re
log D Z °C using log D from 56 and
62 °C
D70 (mins) using logD at
56 °C
F = D70 * (logN0-
logN), s
0.5776 1836.0454 56 1.27 4.10 0.007057422 3.4271
D70 (mins) 12D (s) 58 1.91 12D (s)
3.780941867 2722.2781 60 1.44 5.0813
62 0.93