Using pulse electric fields (PEF) for selective inactivation of coliform bacteria

Abstract

Coliform bacteria usually originate from the intestine, and the contamination typically occurs when there is a lack of sterility in food industry. PEF-induced selective nonthermal pasteurisation method might pasteurise coliform bacteria while leaving the needed bacteria intact. To evaluate this hypothesis, we chose Escherichia coli dh5α (E. coli) strain as a representation of coliform bacteria for this study. We also used Streptococcus thermophilus bacteria strain as a representation of lactobacteria used in milk by-products. The obtained results of PEF application showed that selective death of bacteria after PEF treatment can be induced. PEF was applied on bacteria. Then the clonogenic assay, the metabolic activity, and bacterial growth in the bioreactor were evaluated. By applying PEF treatment on E. coli and S. thermophilus their survival was monitored. We found the PEF parameters under which coliform bacteria E. coli were killed more than 100 times effectively than S. thermophilus. We postulate that it is the result of the bacteria size. Here we show that a PEF-induced selective nonthermal pasteurisation method could be applied in the industry where coliform bacteria can be eliminated while leaving other needed bacteria intact. We showed this by measuring the metabolic activity, the ability to form colonies, and the change in bacteria growth rate in the bioreactor.