99E-23 |
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A. GIRON and T. H. Shellhammer. Food Science and Technology, Oregon State Univ., 100 Wiegand Hall, Corvallis, OR 97331 High hydrostatic pressures can lead to greater ionization in certain buffer systems resulting in a temporary decrease in pH while under pressure. This pH shift may lead to an increase in the effectiveness of antimicrobial compounds by shifting the equilibrium between the dissociated and undissociated forms of the antimicrobials towards the more effective undissociated form. The objective of this study was to determine how antimicrobials and pressure sensitive buffers interact to reduce microbial populations under pressure. The effect of two antimicrobials on a single strain of Lactobacillus plantarum was studied by centrifuging and re-suspending cultures in citrate buffer with antimicrobial (acetic and propionic acids) concentrations within and below the Minimum Inhibitory Concentrations (MIC). The cultures were treated in citrate buffers at pH 3 and at pH=pKa of the acids for 1 minute over a range of pressures. Population reductions were assessed by direct plating. The microbial inactivation observed at pH 3 was similar for all combinations of concentration and antimicrobials (<1 log units, 275MPa; 3.63-5.02 log units, 310 MPa), thus indicating the overriding effect of the low pH. At pH values equal to the pKa of the antimicrobials (pH 4.8 and 4.9), a pressure x antimicrobial interaction was observed. This result may be due to a pressure-induced downward pH shift resulting in decreased ionization of the antimicrobial and consequently greater lethality at higher pressures. At 500MPa, the lowest inactivation was that of the buffer with no antimicrobial (4.37) and the highest was propionic acid within the MIC (>8 log units). Pressure-induced pH shifting of buffered systems may be manipulated to increase the lethality of chemical antimicrobials in pressure processed foods.
Session 99E, Nonthermal Processing: General II
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |