Influence of milk fat on Listeria monocytogenes viability under simulated gastrointestinal conditions and on the viable but not countable state

Abstract

Along with the high nutritional value, milk represents an excellent medium for the growth of certain microorganisms, some of which can be life threatening. Milk fat has been found to affect the survival of L. monocytogenes in milk. The present study aimed to evaluate the effect of milk fat in the survival of L. monocytogenes in milk under simulated gastrointestinal conditions. Four compartments (saliva, gastric, small intestine and large intestine) mimicking the human physiological conditions were established to evaluate the viability of L. monocytogenes inoculated in milk. Given that milk is generally consumed as a breakfast meal, the evaluation was done in the fasted state of the gastrointestinal system. A decrease to 5 log10 CFU/ mL was determined in saliva compartment, in the evaluation after 48 h of cold storage. In the viable but not countable evaluation, L. monocytogenes counts were determined to be 8 log10 CFU/ mL for skim milk and semi-skim milk, and 9 log10 CFU/ mL for whole fat milk in the saliva compartment. Regardless the fat content, L. monocytogenes was not detected in any of the milk groups in the lower parts of the simulated gastrointestinal compartments.