Effect of Hydrostatic Pressure Pulsing on the Inactivation ofSalmonellaEnteritidis in Liquid Whole Egg

Multi-Pulsed High Hydrostatic Pressure Treatment of Foods

Multi-pulsed high hydrostatic pressure (mpHHP) treatment of foods has been investigated for more than two decades. It was reported that the mpHHP treatment, with few exceptions, is more effective than the classical or single-pulsed HHP (spHHP) treatment for inactivation of microorganisms in fruit juice, dairy products, liquid whole egg, meat products, and sea foods. Moreover, the mpHHP treatment could be also used to inactivate enzymes in foods and to increase the shelf-life of foods. The effects of the mpHHP treatment of foods are summarized and the differences between the mpHHP and spHHP are also emphasized.

High hydrostatic pressure treatment for the inactivation of Staphylococcus aureus in human blood plasma

For the past 30years, pressure inactivation of microorganisms has been developed in biosciences, in particular for foods and more recently for biological products, including pharmaceutical ones. In many past studies, the effect of high hydrostatic pressure (HHP) processes on pathogens focused mainly on the effect of an increase of the pressure value. To assure the safety of pharmaceutical products containing fragile therapeutic components, development of new decontamination processes at the lowest pressure value is needed to maintain their therapeutic properties. The aim of this study was therefore to evaluate the impact of the process parameters characterizing high-pressure treatments [such as the pressurization rate (PR) and the application mode (AM)] on the inactivation of pathogens, in particular to determine how these parameters values could help decrease the pressure value necessary to reach the same inactivation level. The effect of these physical parameters was evaluated on the inactivation of Staphylococcus aureus ATCC 6538 which is an opportunistic pathogen of important relevance in the medical, pharmaceutical and food domains. Human blood plasma was chosen as the suspension medium because of its physiological importance in the transfusion field. It was shown that the optimization of all the selected parameters could lead to a high inactivation level (≈5log(10) decrease of the initial bacterial load) at a pressure level as low as 200MPa, underlining some synergistic effects among these parameters. Complete inactivation of the initial bacterial population was achieved for the following conditions: PR=50MPas(-1), AM=5×2min, T≈-5°C and P=300MPa.

Leakage of intracellular UV materials of high hydrostatic pressure-injured Escherichia coli O157:H7 strains in tomato juice

The behavior of high hydrostatic pressure-injured Escherichia coli O157:H7 cells (strain SEA13B88 and a strain from the June-July 1999 Oklahoma juice outbreak) in tomato juice (pH 4.1) and phosphate-buffered saline (PBS; pH 7.2) at final concentrations of 8.4 to 8.8 log CFU/ml, respectively, and treated at 400, 500, and 600 MPa for 40 min at 25 and 35 degrees C with storage at 5 and 23 degrees C for 1,800 min was investigated. Immediately after treatment and every 3 h for 24 h of storage, an aliquot (0.1 ml) was plated on Trypticase soy agar and sorbitol MacConkey agar to determine the percentage of injured population. Leakage of UV materials and possible recovery from injury were investigated. Pressure (600-MPa) treatment at 35 degrees C for 40 min caused a higher percentage of bacterial injury than for 10 min of treatment. A higher percentage of injured population was found among the Oklahoma strain cells than among strain SEA13B88 cells, and differences in viability loss for bacterial strains were determined. The viability loss determined in PBS was 4.8 log for SEA13B88 cells and 5.2 log for Oklahoma cells, while losses of 5.4 and 5.7 log were determined in tomato juice for SEA13B88 and Oklahoma cells, respectively. The leakage of intracellular materials of injured Oklahoma cells was higher than that observed for SEA13B88 cells, but injured Oklahoma cells recovered faster in PBS. However, injured and healthy populations for both strains were below detection in tomato juice stored at 5 degrees C for 1,440 min.