Journal of Food, Agriculture and Environment

Resuscitation of radio frequency electric fields injured Escherichia coli cells in nutrient and non-nutrient media during storage

Author(s):

Dike O. Ukuku ^*, David J. Geveke, Howard Q. Zhang

Recieved Date: 2010-07-10, Accepted Date: 2010-10-29

Abstract:

The need for a nonthermal intervention technology that can achieve microbial safety without altering nutritional quality of liquid foods led to the development of radio frequency electric fields (RFEF) process. However, data on the exact mechanism of bacterial inactivation using RFEF is limited. In this study, we investigated the behavior of RFEF surviving and injured Escherichia coli populations in apple juice treated at 55°C and inoculated in 9 ml phosphate buffer saline (PBS, pH 7.2), 0.1% peptone water (PW, pH 7.2), deionized distilled water (ddH₂O, pH 6.9), tryptone soy broth (TSB, pH 7.1) and apple juice (AJ, pH 3.8) at a final concentration of 3 log CFU/ml. Samples were monitored periodically (0, 2, 4, 6, 8, 10, 12 and 14 h) during storage at 5 and 23 °C by plating 0.1 ml samples on tryptic soy agar (TSA) amended with 0, 1.5 and 3.0 mM calcium chloride and magnesium chloride, and Sorbitol MacConkey agar (SMAC) plates. Cell populations determined on TSA plates without calcium chloride and magnesium chloride averaged 3 log CFU/ml and 3.4 log CFU/ml on plates containing 1.5 and 3.0 mM calcium chloride and magnesium chloride. Though cell populations determined were slightly higher (3.4 log CFU/ml) than the initial 3 log CFU/ml, these numbers were not significantly (p<0.05) different. In liquid media without the cation species, the surviving and injured RFEF-treated cell populations decreased from 3 log to an average of 1.3 log CFU/ml while these populations decreased to only 2.2 log CFU/ml in media amended with these salts. An application of moderate heat (55°C) to the RFEF provided a much greater effect on the injured bacteria populations than when used alone to enhance the inactivation of the bacteria. The results of this study indicate that the ability of added Ca²⁺ and Mg²⁺ to aid cellular repair of RFEF injured E. coli is dependent on both cation species and environmental conditions.

Keywords:

RFEF, injury, inactivation, E. coli, apple juice, magnesium chloride, calcium chloride

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Journal: Journal of Food, Agriculture and Environment
Year: 2010
Volume: 8
Issue: 3&4
Category: Food and Health
Pages: 170-174

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