Title: Pulsed electric field inactivation of E. coli O157:H7 and surrogate bacteria in orange juice Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 15, 2009
Publication Date: July 12, 2009
Citation: Gurtler,J.,Geveke,D.,Rivera,R.,Zhang,H. 2009. Pulsed electric field inactivation of E.coli O157:H7 and surrogate bacteria in Orange Juice [abstract].International Association for Food Protection, 96th Annual Meeting.Grapevine, TX. p.1. Technical Abstract: Introduction: United States FDA juice HACCP rules mandate that orange juice (OJ) processors treat juice for a 5 log reduction of the target pathogen. Thermal pasteurization, however, reduces the sensory characteristics of OJ by removing or altering volatile compounds. Pulsed electric field (PEF) treatment of OJ, an alternative to thermal pasteurization, may preserve these sensory characteristics. Purpose: This study was performed to determine inactivation kinetics of E. coli O157:H7 in OJ by PEF. Another goal was to screen non-pathogenic bacteria with PEF as potential surrogates for O157:H7 for use in biosafety level 1 pilot plant studies. Methods: E. coli O157:H7 (ATCC 43895) and twenty-six strains of non-pathogenic bacteria were screened for sensitivity to PEF in OJ (pH 3.85) with a prototype biolevel 2 PEF system. Cultures were inoculated into OJ at 7 log CFU/ml and treated with PEF at 45 and 50 C, and 22 and 20 kV/cm, respectively. Following this study, survival of the selected surrogate bacterium and O157:H7 were compared at temperatures of 45, 50 and 55 C and field strengths ranging from 6 to 32 kV/cm at a treatment time of 75 us. Injury was determined by plating onto MacConkey agar + 0.3% sodium deoxycholate. Results: Screening of surrogate bacteria revealed that the inactivation of E. coli ATCC 35218 most closely resembled that of E. coli O157:H7. Analysis of covariance, to test for homogeneity of survival curves, determined that the bacteria were statistically indistinguishable at 45 and 50 C, although O157:H7 was slightly more sensitive to PEF than surrogate 35218 at 55 C. Treatment conditions of 55 C and 29 kV/cm resulted in 4.10 log CFU/ml and 100% injury of both bacteria. Significance: These results indicate that non-pathogenic biosafety level 1 ATCC 35218 is a suitable surrogate for E. coli O157:H7 in OJ treated by PEF. Future studies will utilize the surrogate bacterium in scaled-up biolevel 1 pilot plant PEF studies.