Effect of Thermal and Radio Frequency Electric Fields Treatments onEscherichia coli bacteria in Apple Juice

The need for a nonthermal intervention technology that can achieve microbial safety without altering nutritional quality of liquid foods led to the development of the radio frequency electric fields (RFEF) process. However, insight into the mechanism of bacterial inactivation by this technology is limited. In this study, we investigated membrane damage of Escherichia coli bacterial (7.8 log CFU/ml) and leakage of intracellular membrane materials in RFEF treated apple juice at 25 kV/cm and operated at 25°C, 55°C and 75°C for 3.4 milliseconds at a flow rate of 540 ml/min. Damage to cell membrane was detected with Transmission Electron Microscopy (TEM) and leakage of cellular materials was determined with ATP luminometer (20 D) and electrostatic and hydrophobic interaction chromatography used to characterize changes in bacterial cell surfaces. RFEF treatment caused a significant decrease in bacterial cell surface hydrophobicity and loss of relative negative ions compared to heat treatment alone at 55°C and 75°C. Leakage of cellular materials into the media indicated cell damage and TEM observation showed altered intracellular membrane structure in RFEF treated E. coli cells. The results of this study suggest that the mechanism of inactivation of RFEF is by disruption of the bacterial cell surface hydrophobicity and loss of relative negative ions which led to injury and leakage of cellular materials and death.

[1]  Dike O Ukuku,et al.  Effect of hot water and hydrogen peroxide treatments on survival of salmonella and microbial quality of whole and fresh-cut cantaloupe. , 2004, Journal of food protection.

[2]  Michael F. Kozempel,et al.  Radio frequency energy effects on microorganisms in foods , 2002 .

[3]  J. McClements,et al.  Inactivation of Escherichia coli O157:H7 in orange juice using a combination of high pressure and mild heat. , 1999, Journal of food protection.

[4]  C. Brunkhorst,et al.  Inactivation of Escherichia coli in apple juice by radio frequency electric fields , 2004 .

[5]  D. Ukuku,et al.  A combined treatment of UV-light and radio frequency electric field for the inactivation of Escherichia coli K-12 in apple juice. , 2010, International journal of food microbiology.

[6]  M. Koohmaraie,et al.  Cell surface charge characteristics and their relationship to bacterial attachment to meat surfaces , 1989, Applied and environmental microbiology.

[7]  M. Bayer,et al.  The electrophoretic mobility of gram-negative and gram-positive bacteria: an electrokinetic analysis. , 1990, Journal of general microbiology.

[8]  B. Swaminathan,et al.  An Outbreak of Escherichia coli O157:H7 Infection from Unpasteurized Commercial Apple Juice , 1999, Annals of Internal Medicine.

[9]  James L. Hadler,et al.  Outbreaks of Escherichia coli O157:H7 infection and cryptosporidiosis associated with drinking unpasteurized apple cider--Connecticut and New York, October 1996. , 1997, Canada communicable disease report = Releve des maladies transmissibles au Canada.

[10]  J. Mason.  Salmonella enteritidis control programs in the United States. , 1994, International journal of food microbiology.

[11]  In-Koo Rhee,et al.  Differential Damage in Bacterial Cells by Microwave Radiation on the Basis of Cell Wall Structure , 2000, Applied and Environmental Microbiology.

[12]  A S Mazzotta,et al.  Thermal inactivation of stationary-phase and acid-adapted Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in fruit juices. , 2001, Journal of food protection.

[13]  M. Doyle,et al.  Escherichia coli O157:H7 and its significance in foods. , 1991, International journal of food microbiology.

[14]  M. Doyle,et al.  Escherichia coli O157:H7: Epidemiology, Pathogenesis, and Methods for Detection in Food. , 1992, Journal of food protection.

[15]  David J Geveke,et al.  Inactivation of Saccharomyces cerevisiae with radio frequency electric fields. , 2003, Journal of food protection.

[16]  K. Pedersen.  Electrostatic interaction chromatography, a method for assaying the relative surface charges of bacteria , 1981 .

[17]  D. Roy,et al.  Bioluminescence assay for estimating the hydrophobic properties of bacteria as revealed by hydrophobic interaction chromatography , 1991, Applied and environmental microbiology.

[18]  S. Kjelleberg,et al.  The hydrophobicity of bacteria — An important factor in their initial adhesion at the air-water inteface , 2004, Archives of Microbiology.

[19]  D. Fleming,et al.  Outbreak of Salmonella serotype Muenchen infections associated with unpasteurized orange juice--United States and Canada, June 1999. , 1999, Canada communicable disease report = Releve des maladies transmissibles au Canada.

[20]  Rupert G. Miller.  Simultaneous Statistical Inference , 1966 .

[21]  Y. Noda,et al.  Determination of hydrophobicity on bacterial surfaces by nonionic surfactants , 1986, Journal of bacteriology.

[22]  S. Condón,et al.  Membrane Damage and Microbial Inactivation by Chlorine in the Absence and Presence of a Chlorine-Demanding Substrate , 2005, Applied and Environmental Microbiology.

[23]  V. M. Balasubramaniam,et al.  New intervention processes for minially processed juices. , 1999 .

[24]  J. Wells,et al.  An outbreak of diarrhea and hemolytic uremic syndrome from Escherichia coli O157:H7 in fresh-pressed apple cider. , 1993, JAMA.

[25]  J. M. Madden,et al.  Microbial Pathogens in Fresh Produce -- the Regulatory Perspective. , 1992, Journal of food protection.

[26]  R. Hancock,et al.  Binding of polycationic antibiotics and polyamines to lipopolysaccharides of Pseudomonas aeruginosa , 1985, Journal of bacteriology.

[27]  Hydrophobic and electrostatic interaction chromatography for estimating changes in cell surface charge of Escherichia coli cells treated with pulsed electric fields. , 2011, Foodborne pathogens and disease.

[28]  W. Sandine,et al.  Inhibitory action of nisin against Listeria monocytogenes. , 1988, Journal of dairy science.