Evaluation of structural changes and intracellular substance leakage of Escherichia coli O157:H7 induced by ohmic heating.

Abstract

To investigate the effects of ohmic heating (OH) and water bath heating (WB) on the membrane permeability, membrane structure, intracellular organization and leakage of intracellular substances of Escherichia coli O157:H7 at the same inactivation level and at a heating temperature of 72°C. Flow cytometry analysis indicated that membrane permeability of E. coli O157:H7 by OH was comparable to WB at 72°C. Scanning electron microscopy analysis showed that the OH-treated E. coli O157:H7 had greater morphological changes than those of WB-treated ones both at the same inactivation level and the same heating temperature. Transmission electron microscopy analysis showed that both OH and WB caused severe damage on the intracellular organization of E. coli O157:H7 at 72°C. Moreover, OH-treated E. coli O157:H7 had more leakage of intracellular substances than those treated with WB due to the electroporation caused by OH. OH presents considerable potential in inactivation of E. coli O157:H7, especially OH at 10Vcm-1 with a much shorter heating time. The nonthermal effect of OH had a greater effect on the cell membrane of E. coli O157:H7, resulting in more pores and more leakage of intracellular substances out of the E. coli O157:H7 cells. These results could promote the application of OH in food processing.