Thermal Inactivation of Salmonella enterica and Listeria monocytogenes in Quesillo Manufactured from Raw Milk

Abstract

Quesillo is an artisanal Honduran cheese made from raw milk. During fabrication, curd melting is considered a killing step for pathogenic bacteria. This work was aimed at determining the survival of Salmonella enterica and Listeria monocytogenes on inoculated curd packaged in plastic bags and immersed in a water bath at 48, 54, 60, 65, and 70°C for predetermined times. Survival counts of each pathogen were used to estimate D values by linear regression, and z values were estimated by the linear regression of the D values. S. enterica D values ranged from 4.5 min at 60°C to 0.80 min at 70°C ( z = 10 . 7 ° C ). For L. monocytogenes, D values ranged from 6.08 min at 60°C to 0.90 min at 70°C ( z = 11 . 3 ° C ). Validation of 7-log reduction was performed on inoculated curd heated at 65°C for 34.7 min, and recovering enrichment procedures were used for each pathogen. Neither S. enterica nor L. monocytogenes cells were recovered after the enrichment of samples. The results obtained in this study could be applied by Honduran quesillo processors to improve the safety of their products.