Effect of several food ingredients on radiation inactivation of Escherichia coli and Listeria monocytogenes inoculated into ground pork

Abstract

The objective of this study was to examine the effects of several food ingredients on the relative radiation sensitivity (RRS) of Escherichia coli and Listeria monocytogenes inoculated onto ground pork. Garlic, leek, onion, and ginger were prepared in 3 different forms; pressurized, freeze-dried, and 70% ethanol extracted. The prepared food ingredients were subdivided into 2 groups, non-irradiated and irradiated with 5 kGy of gamma irradiation, before addition to ground pork. The prepared food ingredients were added at concentrations of 1% and 5% (w/w) into radiation-sterilized ground pork and inoculated with E. coli and L monocytogenes (10(6) CFU/mL). For E. coli inoculated pork, the most efficient ingredient was ethanol extracted leek (RRS=3.89), followed by freeze-dried ginger and leek (RRS=3.66 and 3.63, respectively) when used without pasteurization. However, when the food ingredients were irradiation-pasteurized, the freeze-dried ginger showed the highest RRS (4.10). When 5% natural materials were added, RRS was the highest for freeze-dried and ethanol extracted onion (4.44 and 4.65, respectively). For L. monocytogenes, the RRS was relatively lower than E. coli in general. The most efficient material was pressurized and freeze-dried onion (RRS=2.13 and 2.08, respectively) at a concentration of 1%. No increase in RRS was observed at increased concentration of food ingredients. These results suggest that the addition of particular food ingredients increased the efficiency of radiation-sterilization. However, changes in RRS were dependent on the species of microorganism as well as the form of the food ingredients. (C) 2011 Elsevier Ltd. All rights reserved.