Membrane damage and viability loss of thermally treated and high hydrostatic pressurized E. coli 0157:H7 and Salmonella spp. in apple juice

Authors: Ukuku, Dike; YAMAMOTO, KAZUTAKA - National Food Research Institute - Japan; BARI, MD. LATIFUL - University Of Dhaka; Mukhopadhyay, Sudarsan; Juneja, Vijay; KAWAMOTO, SHINISHI - National Food Research Institute - Japan

Submitted to: Journal of Food Processing and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2013
Publication Date: 7/20/2013
Publication URL: https://handle.nal.usda.gov/10113/59462
Citation: Ukuku, D.O., Yamamoto, K., Bari, M., Mukhopadhyay, S., Juneja, V.K., Kawamoto, S. 2013. Membrane damage and viability loss of thermally treated and high hydrostatic pressurized E. coli 0157:H7 and Salmonella spp. in apple juice. Journal of Food Processing and Technology. 4:236 doi:10.4172/2157-7110.1000236.

Interpretive Summary: Presence of human bacterial pathogens and spoilage bacteria in minimally processed apple juice is a food safety hazard. There is much interest in understanding the behavior of thermally treated and high hydrostatic pressurized human bacterial pathogens in apple juice during storage in order to enhance processing variables that can achieve total lethality. Salmonella and E. coli O157H:H7 bacteria inoculated in apple juice to a final 7.8 log CFU/ml were thermally treated 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. Injured Salmonella and E. coli populations were observed in juice thermally treated at 55 deg C and above and at pressure treatments at 350 MPa and above. Intracellular UV-materials including the ATP of injured bacteria leaked out of the damaged cells. 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 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.

Technical Abstract: 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.