Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2004
Publication Date: 9/10/2004
Citation: Huang, L. 2004. Thermal resistance of listeria monocytogenes, salmonella heidelberg, and escherichia coli O157:h7 at elevated temperatures. Journal of Food Protection. 67(8):1666-1670.
Interpretive Summary: Steam surface pasteurization such as Vacuum/Steam/Vacuum (VSV) process has been developed to destroy vegetative bacteria attached to food surface. Using high temperature steam (116-157C), this VSV technology could kill some bacteria, but a large number still survive on food surfaces. This research developed a new approach to examine the thermal resistance of three common vegetative pathogens, Listeria monocytogenes, Salmonella Heidelberg, and Escherichia coli O157:H7, at elevated temperatures. Experimental results indicated these organisms did not exhibit extreme thermal resistance at temperatures above 70C. Some other physical factors may be responsible for survival of these organisms on food surfaces. Results from this study may be used to improve and optimize operating conditions of VSV that may lead to a complete elimination of foodborne pathogens, such as Listeria monocytogenes, on the surface of ready-to-eat meats products.
Technical Abstract: A continuous flow apparatus was developed to measure thermal resistance (D and z values) of microorganisms at temperatures above 65°C. This apparatus was originally designed to test if vegetative microorganisms exhibited unusually high thermal resistance that prevented them from being completely eliminated at temperatures (116-157°C) applicable to the vacuum-steam-vacuum processes. The apparatus was composed of a HPLC pump, a heating unit, and a cooling unit. It was designed to measure very small D values (< 1 s). Three randomly selected organisms, Listeria monocytogenes, Salmonella Heidelberg, and Escherichia coli O157:H7 in de-ionized water, were tested in the continuous apparatus at temperatures ranging from 60-80°C. Studies showed that the D values of these organisms ranged from 0.05-20 s. Heating at 80°C was found basically the physical limit of the system. Experimental results showed that L. monocytogenes, S. Heidelberg, and E. coli O157:H7 did not exhibit unusual heat resistance. The conditions used in the VSV processes should have completely eliminated organisms such as L. monocytogenes, S. Heidelberg, and E. coli O157:H7 if present on food surfaces. The incomplete destruction of bacteria during VSV may be attributed to that the surface temperatures are below the steam temperatures and that bacteria are hidden underneath the surface.