Behavior of Native Food Isolates of Listeria monocytogenes and Listeria innocua under the Influence of Selected Cultural Attributes and Heat and Cold Treatments.

The present investigation assesses the influence of cultural attributes and heat and cold treatments
on the behavior of native toxigenic L. monocytogenes CFR 1302 and non-toxigenic L. innocua CFR 1304
in selected medium. The growth responses of L. monocytogenes and L. innocua under the influencing
factors of storage temperature (10-40°C), pH level (5.5-7.5), and storage period (6-48 h) in brain heart
infusion and nutrient broths revealed closeness between observed and predicted populations. Response
surface plots were generated for the growth behavior of the two test cultures as a function of pH level.
The toxigenic L. monocytogenes CFR 1302 could reach a higher viable population. The effect of heat
treatment on Listeria spp. in selected five heating menstra showed the lowest D-value of 3.7 min at
60°C for L. innocua CFR 1304 in Milli-Q water to the highest of 8.4 min at 56°C for L. monocytogenes
CFR 1302 in skim milk. The average z-value across the heating menstra for L. monocytogenes was 27.3°C
as against that of 22°C for L. innocua. In the case of cold treatment, storage of 4 and 8°C resulted in
appreciable increase in counts of L. monocytogenes CFR 1302 from the initial inoculum introduced in
selected media. At -20°C, there was a slight decrease in the viable population. The research data helps
to predict the viable populations of L. monocytogenes as a part of risk assessment in the food chain.
This is of significance in providing safe and healthy food to human population.