Thermal inactivation kinetics of Salmonella Typhimurium in alheira sausage batter

Previous studies have highlighted the need to implement better microbiological control and process standardisation during the production of alheiras sausages, in particular during the stage of heat treatment. Alheira is a non-ready-to-eat sausage from Northern Portugal, which although at low prevalence, has shown survivability of Salmonella spp. throughout maturation. The objective of this work was to characterise the heat resistance of Salmonella Typhimurium (ST) in alheira sausage batter.

Two batches of alheira batter were obtained from a producer and inoculated with a ST overnight culture to reach ~7.0 log CFU/g. Bags containing well-spread 10-g alheira batter were submitted in duplicate to temperatures of 63°, 60°, 57° and 54 °C in an immersion bath, and sampled at 6 different time points. The quantification of ST on XLD plates was performed within two hours of the experiment.

A log-linear primary model fitted to each of the inactivation curves estimated the death rates of ST in alheira batter to be 0.038 (SE=0.008), 0.126 (SE=0.003), 0.273 (SE=0.063) and 2.872 (SE=0.763) log CFU/min at 54 º, 57 º, 60 º and 63 ºC, respectively, with coefficients of determination ranging between 0.914 and 0.987. Through a Bigelow model, the D-value (time needed to reduce ST in 1 log) was modelled as a function of temperature, resulting in a log D* of 2.302 (SE=0.304), corresponding to 200 minutes at 50 ºC to reduce ST in 1 log, and a z-value of 5.016 (SE=0.839) ºC. This model enables the prediction of D values and lethality times at other temperatures. For instance, to reach the 7.0 log reduction lethality of Salmonella spp. sought in sausages, the centre of the alheiras should be kept for 9.0 seconds at 70 °C.

This study characterised for the first time the thermal inactivation kinetics of Salmonella Typhimurium in a traditional Portuguese sausage, and will be useful to producers for designing and controlling their thermal processes during alheira manufacture.