Thermal inactivation of Listeria monocytogenes in the Shaka agitated reciprocal retort: Influence of food matrix rheology and fat content

Summary

The effect of food matrix rheology and fat content on thermal inactivation of Listeria monocytogenes in the Shaka agitated retort (final retort temperatures of 59, 64, and 69 °C) was investigated using four fish-based artificial food model systems: low-viscosity liquid (liquid), high-viscosity liquid (xanthan), and emulsions containing 10% and 20% fat (emulsion 10% and emulsion 20%). Model system rheology, quantified by the consistency index K and the flow behaviour index n, influenced the thermal load to which the systems were exposed during treatments. Thermal loads followed the order liquid ≥ emulsion 10% ≥ emulsion 20% ≥ xanthan, a trend which was also valid for the sublethal injury induced to the cells. Log reductions followed the order liquid ≥ emulsion 10% ≥ xanthan ≥ emulsion 20%, indicating a protective effect of an increased fat content, not related to heat transfer differences. Between approximately 59 and 62 °C, the temperature range over which the largest portion of the inactivation was achieved, the maximum specific inactivation rate kmax followed the same trend as the log reductions. Overall, the effect of food matrix rheology on inactivation efficacy could be linked to heat transfer dynamics, while the effect of fat content was more complex.