Influence of type of microorganism, food ingredients and food properties on high-pressure carbon dioxide inactivation of microorganisms

High pressure carbon dioxide (HPCD) treatment is currently considered as an attractive non-thermal process for preserving food. Industrial application of this technique requires, among others, systematic (quantitative) data on the inactivation of food relevant pathogenic and spoilage microorganisms, and in-depth information on the effect that the composition and the properties of a food matrix have on the inactivation efficacy. rst objective of this study, therefore, is to evaluate and compare the HPCD susceptibility of several food pathogens and spoilage microorganisms under the same treatment conditions. In the second part, the influence of different food components (NaCl, oil, starch, whey protein and emulsifier) and food properties (pH, fluid viscosity and water activity) on the inactivation efficacy of HPCD was determined. For the first aim, a range of Gram-negative and Gram-positive bacteria, yeasts and spores were treated with pressurized CO2 at 10.5 MPa and 35 °C during 20 min. Bacterial susceptibility towards HPCD treatments followed the sequence Gram-negative ≈ Gram-positive > yeasts > spores and appeared to be related to the acid resistance of the organisms. To study the effect of different food compounds on HPCD inactivation, the reduction degree of Pseudomonas fluorescens was determined in media with and without these components at 10.5 MPa and 35 °C after 5 or 20 min, depending on the tested component. NaCl and the emulsifiers Tween 80 and sucrose stearate enhanced bacterial reduction, while oil reduced the bactericidal efficacy of HPCD. Starch and whey proteins did not influence inactivation. Finally, the influence of pH, fluid viscosity and water activity was investigated by determining the reduction of P. fluorescens at 10.5 MPa and 35 °C in suspensions from which the pH, viscosity and water activity were adjusted with respectively NaOH or HCl, gelatin or polyethylene glycol, and sucrose, NaCl or glycerol. Treatment time depended on the studied food property with 5 min for the pH experiments, while other experiments lasted 20 min. The results indicated that P. fluorescens cells became more sensitive to HPCD treatments at low pH and viscosity. Not water activity but the kind of soluble solute used to lower water activity influenced inactivation. High NaCl-concentrations lead to total inactivation, while sucrose and glycerol strongly protected the cells against inactivation.