High pressure processing of milk: Modeling the inactivation of psychrotrophic Bacillus cereus spores at 38-70 °C

Bacillus cereus is a pathogen that can grow in foods and beverages with low acidity. The main objective of this work was to model the inactivation of psychrotrophic B. cereus spores in reconstituted milk treated by high pressure (HPP) combined with a thermal process, and to compare it with thermal inactivation kinetics. First, the effect of HPP pressure (200, 400 and 600 MPa) for up to 40 min at 70 °C on B. cereus spores was investigated. A pressure increment from 200 to 600 MPa slightly reduced the spore numbers in the reconstituted milk. Then the influence of temperature at 600 MPa on spore inactivation for up to 40 min was studied. Increasing the HPP temperature from 38 to 70 °C increased the spore inactivation in milk by 3.5 log. The 600 MPa combined with heat enhanced the spore inactivation in milk, requiring a temperature 20 °C lower to achieve the same spore inactivation. However, for a 5 log spore inactivation, the pressure-thermal process required a higher specific energy than the thermal processing. The resistance of two psychrotrophic strains of B. cereus spores in milk was also investigated and showed similar results. The Weibull model described spore inactivation by pressure-heat, whereas the first order kinetics was more appropriate for the thermal inactivation alone. The results of this study confirmed the advantage of HPP technology to further increase the thermal inactivation of B. cereus spores in milk.