Behavior of pulsed electric fields injured Escherichia coli o157:H7 cells in apple juice amended with pyruvate and catalase

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 23°C 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 μs at 25, 35, 45 and 55°C, at a fl ow rate of 120 ml/min. The juices collected were amended with pyruvate and catalase (0 to 0.1%) and then stored at 5 and 23°C 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 55°C 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. © 2010 Ukuku D, et al.