Acid Adaptation Enhances Tolerance of O157:H7 to High Voltage Atmospheric Cold Plasma in Raw Pineapple Juice

Pathogens that adapt to environmental stress can develop an increased tolerance to some physical or chemical antimicrobial treatments. The main objective of this study was to determine if acid adaptation increased the tolerance of O157:H7 to high voltage atmospheric cold plasma (HVACP) in raw pineapple juice. Samples (10 mL) of juice were inoculated with non-acid-adapted (NAA) or acid-adapted (AA) to obtain a viable count of ~7.00 log CFU/mL. The samples were exposed to HVACP (70 kV) for 1-7 min, with inoculated non-HVACP-treated juice serving as a control. Juice samples were analyzed for survivors at 0.1 h and after 24 h of refrigeration (4 °C). Samples analyzed after 24 h exhibited significant decreases in viable NAA cells with sub-lethal injury detected in both NAA and AA survivors ( < 0.05). No NAA survivor in juice exposed to HVACP for 5 or 7 min was detected after 24 h. However, the number of AA survivors was 3.33 and 3.09 log CFU/mL in juice treated for 5 and 7 min, respectively ( < 0.05). These results indicate that acid adaptation increases the tolerance of to HVACP in pineapple juice. The potentially higher tolerance of AA O157:H7 to HVACP should be considered in developing safe juice processing parameters for this novel non-thermal technology.