Journal of Food Processing & Technology

Abstract

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 and Shinishi Kawamoto

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 (TDT) disk and high hydrostatic pressure treatments were investigated. Salmonella spp. and E. coli O157H:H7 bacteria were inoculated in apple juice to a final 7.8 log10 CFU/ml and were thermally treated with TDT disks at 25, 35, 45, 50, 55 and 60°C for 4 min or pressurized at 350, 400 and 450 MPa at 25, 35, 45, 50, 55 and 60°C for 20 min. Sublethal injury, leakage of UV- materials and viability loss as a function of membrane damage of these bacterial pathogens was investigated by plating 0.1 ml of treated and untreated samples on non selective Trypticase Soy Agar (TSA) and selective Xylose Lysine Sodium Tetradecylsufate (XLT4) for Salmonella and Cefixime Potassium Tellurite Sorbitol-MacConkey (CT-SMACK) agar plates for E. coli bacteria with incubation at 36°C for 48 h. Sub-lethal injury occurred in Salmonella spp. and E. coli populations thermally treated with TDT disk at 55°C and above and at a pressure treatments of 25°C and above. Leakage of intracellular UV-materials and ATP of TDT disk injured cells was lower than the values determined from pressurized cells. Similarly, recovery of TDT injured cells occurred faster than pressurized cells during storage of treated samples at 22°C. The results of this study indicate that pressure treatment of 350 MPa at 35°C for 20 min and thermal treatments of 55 and 60°C and immediate storage of treated samples at 5°C will inhibit recovery and complete inactivation of injured bacteria in apple juice and therefore, will enhance the microbial safety of the treated juice.