Baroinactivation of Staphylococcus epidermidis - mathematical model and its verification using human and cow milks

Staphylococcus epidermidis, commonly found on the human skin, may contaminate human milk. High-pressure pasteurisation of human milk under normal temperature preserves the majority of its protective agents. The objective of this study was to acquire baroinactivation data and develop a model for model solutions of pH = 6.4 to 7.2 and water activity aw = 0.99 in which baroinactivation of Staphylococcus epidermidis takes place. Decontamination data manifested exponential kinetics and the resulting model was described by the following equations: Dp = Dp, ref x 10 (Pref - P)/Z, Z = -123.90 pH2 + 1635.54 pH - 5210.49; Dp, ref = -8.89 pH2 + 121.02 pH - 408.34. The developed model was verified using pasteurised human milk and UHT-treated skimmed cow milk. The agreement between the experimental data and model-based prediction was very good for human milk. The application of a pressure of 350 MPa for 10 min decreased the concentration of the working suspension of S. epidermidis in the model substrate by a minimum of five orders of magnitude.