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Membrane Damage and Viability Loss of E. coli O157:H7 and Salmonella spp in Apple Juice Treated with High Hydrostatic Pressure and Thermal Death Time Disks

Dike O. Ukuku, Kazutaka Yamamoto, Md L. Bari, Sudarsan Mukhopadhaya, Vijay Juneja, Shinishi Kawamoto
Journal of food processing & technology 2013 v.04 no.06 pp. -
Escherichia coli O157, Salmonella, adenosine triphosphate, apple juice, bacteria, cell membranes, cell viability, death, food contamination, food sanitation, heat treatment, high pressure treatment, microbial contamination, pathogen survival, pathogens, scanning electron microscopy, sterilizing
Differences in membrane damage including leakage of intracellular UV-materials and loss of viability of Salmonella spp. and Escherichia coli O157:H7 bacteria in apple juice following thermal death time disk (TDT) and high hydrostatic pressure treatments were investigated. Salmonella and E. coli O157H:H7 bacteria were inoculated in apple juice to a final 7.8 log CFU/ml and were thermally treated with TDT disks at 25, 35, 45, 50, 55 and 60 deg C for 4 min or pressurized at 350, 400 and 450 MPa at 25, 35, 45, 50, 55 and 60 deg C for 20 min. Sublethal injury, leakage of UV- materials including adenosine triphosphate (ATP) and viability loss as a function of membrane damage of these bacterial pathogens were investigated. Also, scanning electron microscopy was used to characterize difference in membrane damage. Sub-lethal injury occurred in Salmonella and E. coli populations thermally treated with TDT disk at 55 deg C and above and at pressure treatments of 350 MPa and above. Leakage of intracellular UV-materials and ATP of thermal injured cells were lower than the values determined from pressurized cells. Similarly, recovery of thermal injured cells occurred faster than pressurized cells during storage of treated samples at 22 deg C. The results of this study indicate that pressure treatment of 350 MPa at 35 deg C for 20 min and thermal treatments of 55 and 60 deg C and immediate storage of treated samples at 5 deg C will inhibit recovery of injured bacteria in apple juice and therefore, will enhance the microbial safety of the treated juice.