Study of the effect of fermentation temperature, drying temperature, caliber size, starter culture and sodium lactate on Listeria monocytogenes inactivation during salami production.

The effect of fermentation and drying temperatures, caliber and sodium lactate on Listeria monocytogenes inactivation was studied in salami, produced in a pilot scale, inoculated with 107 CFU/g of Listeria innocua ATCC® 33090 as a surrogate microorganism for L. monocytogenes. Fermentation temperature varied between 24 and 30 °C, drying temperature between 14 and 20 °C, caliber between 5.1 and 13.2 cm and sodium lactate initial concentrations in salamis were 0 and 2 %. L. innocua counts, pH and water activity were determined in salamis over time. Sodium lactate (2 %) decreased pH drop and Listeria inactivation during fermentation. Baranyi & Roberts equation was used to fit the experimental data and to estimate, for each test condition, inactivation rate (k), initial (Y0 ) and final counts of L. innocua (YEND ). Total inactivation was calculated as Y0 minus YEND (Y0 -YEND ). Then, using a Box Benkhen experimental design a quadratic model for k and a two-factor interaction model (2FI) for Y0 - YEND were obtained as functions of fermentation temperature, drying temperature and caliber size. The models predicted that maximum k and Y0 -YEND , -2.62 ± 0.14 log10 CFU/g/day and 4.5 ± 0.1 log10 CFU/g, respectively, would be obtained fermenting at 30 °C and drying at 20 °C regardless of caliber. Drying at 14 °C allowed Listeria growth until a water activity (aw ) of 0.92 was reached. Therefore, if initial Listeria contamination is high (3 log10 CFU/g) drying at low temperatures will compromise product safety.