Location: Food Science Research
2008 Annual Report
Research has shown that dissolved oxygen plays a key role in the destruction of bacteria in acid solutions. Acid solutions with and without dissolved oxygen were tested for the ability to kill bacteria. It was found that the trace amounts of dissolved oxygen was enough to greatly accelerate killing of bacteria by acid. This research may be used to accelerate acid killing of bacteria in acid and acidified foods. This research addresses National Program 108 (Food Safety) Component 1 (Pathogens, Toxins and Chemical Contaminants) problem 1.2 (Pathogens, Toxins and Chemical Contaminants Postharvest) sub-problem 1.2.3 (Production and Processing Ecology).
A method for determining the numbers of live bacteria in liquids or removed from surface films was investigated. The method does not require traditional plating techniques that are used for counting the bacteria present in a sample, which could consist of a food or food extract. The method under investigation uses a gene amplification technique called Polymerase Chain Reaction (PCR) (used to amplify DNA), that allows a quantitative measure of how much genetic material is being amplified and can be used to determine how many bacteria were present in a sample being tested. A major problem with this technique is that genetic material from both live cells and dead cells can be amplified and can contribute to the estimated count of bacteria present. In this research, it was found that a special dye treatment can be applied to the sample containing bacterial cells prior to isolating the DNA, and this will only allow the amplification of genes from live bacteria, not dead cells. Although this technique had been previously reported, this research refined the method and has demonstrated accurate counting of live cells in samples that had a high concentrations of dead cells. This research addresses National Program 108 (Food Safety) Component 1 (Pathogens, Toxins and Chemical Contaminants) problem 1.2 (Pathogens, Toxins and Chemical Contaminants Postharvest) sub-problem 1.2.1 (Detection and Validation).
This research directly addresses the National Program Action Plan for Food Safety 108, Component 1 (Pathogens, Toxins and Chemical Contaminants) section 1.2.3, to understand the physiological status of bacteria and survival in niches. Aspects of this work may also lead to process intervention strategies (section 1.2.4).
In response to concerns by the United States Food and Drug Administration (FDA), and in conjunction with the principal trade association for the acidified foods industry (Pickle Packers International), research was carried out to determine the conditions needed to assure the destruction of disease causing bacteria in acidified foods. Acidified foods are foods to which acid or acid ingredients are added to preserve the food. The results of this project showed the holding times and temperatures needed to assure the safety of acidified foods that are not typically heat treated, and basic research was also carried out to determine the effects of organic acids on the survival of bacteria in acid and acidified foods. Safe production practices and industry process filings required for the production and sale of acidified foods in the United States are now based on this research. The FDA now uses the research and data as the basis for determining safe production practices for acidified foods in the United States.
5.Significant Activities that Support Special Target Populations
Pan, Y. and Breidt, F. 2007. Enumeration of Viable Listeria monocytogenes Cells by Real-Time PCR with Propidium Monoazide and Ethidium Monoazide in the Presence of Dead Cells. Appl. Environ. Microbiol. 73(24):8028-8031
Breidt, F., Hayes, J.S., Mcfeeters, R.F. 2007. Determination of 5-log reduction times for food pathogens in acidified cucumbers during storage at 10 and 25°C. Journal of Food Protection. 70(11):2638-2641.