Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/21/2009
Publication Date: 11/11/2009
Citation: Ukuku, D.O., Zhang, H.Q., Latiful, B., Yamamoto, K., Kawamoto, S. 2009. Leakage of Intracellular UV Materials of High Hydrostatic Pressure-Injured Escherichia Coli O157:H7 Strains in Tomato Juice. Journal of Food Protection. 72(11):2407-2412. Interpretive Summary: Researchers have used high pressure processing (HHP) treatment to kill bacteria in foods. However, the detail of how this pressure kills bacteria is limited. In this study, we investigated the ability of injured cells of Salmonella Enteritidis and E. coli O157:H7 to repair and survive in tomato juice and phosphate buffer saline (PBS) treated with high pressure processing. Most injury to E. coli O157:H7 and Salmonella cells occurred in PBS rather than in tomato juice, at lower pressure treatment (350MPa), and at 23 C and 35 C. Bacterial injury led to leakage of the internal substances of the bacteria. The populations of injured bacteria in PBS and tomato juice declined further during storage at 5C for 24 h. No injured cells were recovered in tomato juices treated with 450 MPa pressure for 20 min at 23 C or 35 C after storage for 24 h. The results of this study suggest the recovery of Salmonella and E. coli cells after HHP treatment in PBS but not in tomato juice. Therefore, pressure (450 MPa) treatment of tomato juice for 20 min at 23 C or 35 C will kill most bacteria in the tomato juice, enhancing their microbial safety.
Technical Abstract: The effect of high hydrostatic pressure (HHP) treatment on inactivation, injury and recovery of Salmonella Enteritidis and Escherichia coli O157:H7 cocktail inoculated in tomato juice (pH 4.1) and phosphate buffer saline (PBS. pH 7.2) at 8.0 log CFU/ml and treated at 350, 400, 450 MPa for 20 min at initial temperatures of 23 C and at 35 C was investigated. Sublethal injury, leakage of intracellular substances and viability loss of E. coli O157:H7 and Salmonella Enteritidis were investigated by plating 0.1 ml on Trypticase Soy Agar (TSA), Sorbitol MacConky Agar (SMAC) and Xylose Lysine Sodium Tetradecylsufate (XLT4). Treated samples were stored at 5 'C, 10 C and 23 C and periodically (0 to 15 days) were monitored for survival and recovery of injured cells. Pressure treatment at 450 MPa (35 C) for 20 min resulted in an average of 6.2 and 5.3 log reductions of E. coli and Salmonella cells in tomato juice, respectively, and 4.3 and 3.5 log reductions in PBS. Pressure treatment at lower temperature (23 C) for 20 min led to 4.1 and 3.3 log reduction of E. coli and Salmonella cells in tomato juice and a 3.8 and 3.3 log in PBS. A higher percentage of bacterial injury for E. coli and Salmonella cells occurred at 350 MPa treatments at 23 C and 35 C in PBS than in tomato juice. Unlike in PBS, no injured cells were recovered in tomato juices treated with 450 MPa pressure for 20 min at 23 C or 35 C after storage for 24 h. The results of this study suggest recovery of Salmonella and E. coli after HHP treatment in PBS while this effect was not observed in tomato juice.