Submitted to: Journal of Microbial and Biochemical Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2010
Publication Date: 9/22/2010
Citation: Ukuku, D.O., Yuk, H., Zhang, H.Q. 2010. Behavior of pulsed electric field injured Escherichia coli O157:H7 cells in apple juice amended with pyruvate and catalase. Journal of Microbial and Biochemical Technology. 2(6):134-138. Interpretive Summary: Pulse Electric Field (PEF) treatments, a non-thermal process, have been reported to injure and kill bacteria in liquid foods. This technology can be used to kill Escherichia coli in apple juice. However, some E. coli may survive the PEF process as injured cells. There is no information available regarding the conditions required for resuscitation of PEF injured Escherichia coli O157:H7 bacteria. In this study, we investigated the effect of adding catalase and pyruvate to PEF injured E.coli cells in apple juice during storage. We found that the addition of catalase and pyruvate aided recovery of injured cells and reduced these populations significantly. This result suggests that PEF treatment may destruct intrinsic catalase and pyruvate in E. coli. This information will enable juice processors using this technology to modify their treatment parameters to improve the PEF process for enhancing the safety of apple juice.
Technical Abstract: Pulse Electric Field (PEF) treatment has been used to inactivate bacteria in liquid foods. However, information on the behavior of PEF injured Escherichia coli bacteria in media during storage at 5 and 23C are limited. In this study, we investigated the fate of E. coli O157:H7 cells at 6.8 log CFU/ml in apple juice treated with PEF at 7.2 kV/cm and 32.2 kV/cm, 18.4 A with pulse width of 2.6 us at 25, 35, 45 and 55C, at a flow rate of 120 ml/min. The juices collected were amended with pyruvate and catalase (0 to 0.1%) and then stored at 5 and 23C for 24 h. Periodically (0, 3, 6, and 24 h), 0.1 ml of the treated sample was plated on Sorbitol MacConkey Agar (SMAC) and Tryptic Soy Agar (TSA) amended with catalase and pyruvate to determine percent injury, viability loss and behavior of injured cells. PEF voltage at 32.2 kV/cm and treatments at 35, 45 and 55C led to significant decline in the surviving cell populations than treatment at 7.2 kV/cm. The injured populations in control media were higher than media amended with pyruvate and catalase suggesting possible recovery of PEF injured E. coli cells.