Inactivation of Alicyclobacillus acidoterrestris Grown at Different pH Values using Dielectric Barrier Discharge-atmospheric Cold Plasma
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Abstract:
The effects of dielectric barrier discharge-atmospheric cold plasma (DBD-ACP) on the inactivation of Alicyclobacillus acidoterrestris grown at different pH values (3.2, 3.6, 4.0, and 4.4) were investigated. The inactivation efficiency against A. acidoterrestris grown optimally at pH 4.0 was the lowest. An increase in pH (4.4) and a decrease in pH (3.2, 3.6) both lead to increased lethality (P<0.05). The inactivation on A. acidoterrestris grown at pH 4.0 using DBD-ACP was 4.8 log under 30 kV treatment for 2 min and was 5.9, 5.4, and 5.1 log for A. acidoterrestris grown at pH 3.2, 3.6, and 4.4, respectively. The difference in the inactivation of A. acidoterrestris cells cultured at different pH using DBD-ACP could be attributed to the changes in morphology and membrane fatty acid composition of A. acidoterrestris cells. Scanning electron microscopy (SEM) observations indicated that the bacteria cultured at pH 3.2 and 3.6 displayed abnormal elongation, which was more obvious at pH 3.2, indicating an increased susceptibility to DBD-ACP. The gas chromatography-mass spectrometry (GC-MS) results indicated that the relative content of cyclohexaneundecanoic acid (67.86%) was significantly increased at pH 4.4, compared to that at optimum pH 4.0, whereas the cyclopentanetridecanoic acid content (22.21%) decreased (P<0.05), facilitating the accumulation of oxygen free radicals and other components generated by DBD-ACP in the cell membranes, and causing bacterial death. The higher tolerance of A. acidoterrestris to DBD-ACP is related to the changes in its fatty acid composition and morphology of the cell membrane.
