Mathematical modeling of yeast inactivation of freshly squeezed apple juice under high-pressure carbon dioxide.

The number of data sets available in literature regarding inactivation kinetic of microorganisms at low temperature, demonstrate an increasing attention to new technologies for food preservation at ambient temperature. Nevertheless, no reliable modeling, capable to describe complex inactivation curves, such as the ones due to dense gas pasteurization with a log-linear behavior, have been developed thus far. In this respect, the main aim of this work is to analyze and model experimental data of dense carbon dioxide yeast pasteurization of natural apple juice at different condition of temperature (25-36°C) and sample volume (5-10 ml). The Weibull model modified by Albert and Mafart was verified to be an interesting model capable to take into account CO2 inactivation kinetic, with a first phase with a shoulder, a second phase with a log-linear shape, and a final phase with a tailing with either a non-zero or a zero asymptote. Clearly, the results obtained shows that an increase in temperature decreases the time needed for the same inactivation efficiency; the residual yeast concentration of N(RES), a thermodynamic parameter, results volume independent, and temperature dependent; the treatment time required to reach 90% of inactivation results temperature dependent, with a sample volume of 5 ml; at 100 bar - 25°C-10 mL a shoulder effect is evident in the inactivation kinetic. The model can be considered a new useful tool to predict new CO2 pasteurization data at different operative conditions.