EFFECT OF STORAGE AT 4 AND 10C ON THE GROWTH OF LISTERIA MONOCYTOGENES IN AND ON QUESO FRESCO

A five-strain rifampicin-resistant Listeria monocytogenes cocktail (ca. 3.0 log(10) cfu/g) was introduced as a postpasteurization contaminant in queso fresco (QF) that was manufactured using a commercial procedure. L. monocytogenes was either inoculated into (IN) the curds before forming the cheese block or onto (ON) slices (52-66 g), individually vacuum-packed and stored at 4 and 10C. Growth was monitored for up to 35 days. Gompertz analyses showed small differences in lag time because of temperature, but growth rate and generation time were faster at 10C than at 4C. After 20 days for both the IN and the ON treatments, the maximum population density was 7.80 +/- 0.17, regardless of the storage temperature. These results indicate that QF manufacture must be conducted using Good Manufacturing Practices and under hygienic conditions, and that the use of antimicrobials and/or postprocessing interventions is necessary to prevent the presence and growth of L. monocytogenes.