Submitted to: Food Research International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2003
Publication Date: 1/29/2003
Citation: GEVEKE, D.J., KOZEMPEL, M.F. PULSED ELECTRIC FIELD EFFECTS ON BACTERIA AND YEAST CELLS. FOOD RESEARCH INTERNATIONAL. 2003. v. 27. p. 65-72. Interpretive Summary: We studied the effects of high electric fields on microorganisms in water at room temperature. This technique is one of the promising alternatives to conventional, thermal pasteurization. Its major advantage is that temperature sensitive foods can be pasteurized while preserving their unique functional properties and flavor. Suspensions of Escherichia coli, Listeria innocua, Saccharomyces cerevisiae, and Candida stellata were studied. Numerous, short pulses of 12.5 kV/cm were applied at a maximum temperature of 30C. The microbial concentrations of S. cerevisiae and C. stellata were reduced more than 99.9 percent. A similar reduction in the concentration of L. innocua required lowering the pH to 3.8. The reduction of E. coli was only 90 percent and was not improved by lowering the pH. Microorganisms are generally assumed to be more sensitive at acidic conditions; however, the results of this study indicate that this assumption is not always valid. Hence, the effectiveness of pulsed electri fields on each target microorganism in each food should be tested on a case-by-case basis to ensure safety.
Technical Abstract: Cell suspensions of yeasts and bacteria in the exponential growth phase were subjected to pulsed electric fields of 12.5 kV/cm strength to study inactivation. Up to 20 pulses of 0.3 ms duration were applied at a maximum temperature of 30C. Reductions of greater than 3 log were obtained for the yeasts Saccharomyces cerevisiae and Candida stellata. These reductions were due to electrical effects and not to thermal effects. Reductions of approximately 1 log or less were obtained for the bacteria Escherichia coli and Listeria innocua. However, by lowering the pH of the L. innocua suspension from 6.6 to 3.8, a 3 log reduction was achieved. A similar effect of pH on the inactivation of E. coli was not observed. The results may have implications for treating foods with pulsed electric fields; inactivation of some microorganisms may be independent of acidity.