title: Kinetic analysis and modelling of combined high-pressure-temperature inactivation of the yeast Zygosaccharomyces bailii.
abstract: Eight foodborne yeasts were screened for sensitivity to high-pressure (HP) inactivation under a limited number of pressure-temperature combinations. The most resistant strains were Zygoascus hellenicus and Zygosaccharomyces bailii. The latter was taken for a detailed study of inactivation kinetics over a wide range of pressures (120-320 MPa) and temperatures (-5 to 45 degrees C). Isobaric and isothermal inactivation experiments were conducted in Tris-HCl buffer pH 6.5 for 48 different combinations of pressure and temperature. Inactivation was biphasic, with a first phase encompassing four to six decades and being described by first-order kinetics, followed by a tailing phase. Decimal reduction times (D) were calculated for the first-order inactivation phase and their temperature and pressure dependence was described. At constant temperature, D decreased with increasing pressure as expected. At constant pressure, D showed a maximum at around 20 degrees C, and decreased both at lower and at higher temperatures. A mathematical expression was developed to describe accurately the inactivation of Z. bailii as a function of pressure and temperature under the experimental conditions employed. A limited number of experiments in buffer at low pH (3-6) suggest that the model is, in principle, applicable at low pH. In apple and orange juice however, higher inactivation than predicted by the model was achieved.
authors.affiliation: Katholieke Universiteit Leuven, Department of Food and Microbial Technology, Belgium.
authors.forename: K M
authors.initials: KM
authors.lastname: Reyns
authors.forename: C C
authors.initials: CC
authors.lastname: Soontjens
authors.forename: K
authors.initials: K
authors.lastname: Cornelis
authors.forename: C A
authors.initials: CA
authors.lastname: Weemaes
authors.forename: M E
authors.initials: ME
authors.lastname: Hendrickx
authors.forename: C W
authors.initials: CW
authors.lastname: Michiels
mesh_terms: D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008962:Models, Theoretical; D011312:Pressure; D013696:Temperature; D020068:Zygosaccharomyces / Q000254:growth & development*