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United States Department of Agriculture

Agricultural Research Service

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Research Project: Bridging the Gap: Integrated Research and Extension in Support of Small Processors of Acidified Canned Foods

Location: Food Science Research

2013 Annual Report


1a.Objectives (from AD-416):
1. To fill knowledge gaps in the regulatory framework for acidified foods, including:

a. Development of linear models for thermal processing of acidified foods with pH above 4.1 (pH 4.1-4.6) that meet microbial-destruction targets.

b. Determination of the pH, organic acid, and environmental conditions (temperature, dissolved oxygen) that allow spoilage bacilli such as Alicyclobacillus species, Bacillus coagulans, Bacillus licheniformis, and others to grow and potentially raise pH of acidified foods.

c. Determine cold fill hold times and temperatures that assure safety for food with a pH value above pH 3.3.


1b.Approach (from AD-416):
This work will include the use of novel organic acid additives to acidified foods such as fumaric acid, which have recently been shown to be highly effective in killing enteropathogenic E. coli strains in acidified foods.

Methods will include determination of the efficacy of combined organic acids on killing E. coli O157:H7 (and other enteropathogenic serotypes), Listeria monocytogenes, and Salmonella strains in acidified foods. Mathematical models of killing kinetics will be developed. Microbiological testing will include fractional factorial experimental design, spiral plating with automated plate reading, and 96 well microtiter plate most probable number techniques. These methods will significantly reduce the supplies and time needed to generate robust and repeatable killing curve data. Inoculated pack studies will include acidified vegetable products such as cucumber pickles (which lack antimicrobial phytochemicals), taking into account bacterial strain and product variation, pre-conditioning cells to acid stress, the sensitivity of acid injured cells to plating media, the effects of ionic strength and dissolved oxygen on acid stress, and other variables that could lead to “fail dangerous” conclusions.


3.Progress Report:

The project is related to in-house objectives 1 and 3, to assure a 5-log reduction in acid tolerant pathogens in both in acidified foods, and the results will support FDA process filings by industry.

To assure a 5-log reduction of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes, acidified foods that are not thermally processed must be held before sale and distribution to allow time for the organic acid(s) to kill vegetative bacterial pathogens. Acidified food products that cannot meet the current requirements or be heat processed without significantly altering sensory properties include dressings, mayonnaises, and some pickled vegetable products. A 5-log reduction of vegetative pathogens in these products may be defined as a critical control point for safe production of these products under the Food Safety Modernization Act. Testing many different product formulations for a variety of acidified foods to demonstrate a 5-log reduction in bacterial pathogen levels may be impractical. Even small changes in product formulation would require new microbiological tests to determine safe processing conditions. Our research focused on common ingredients, such as acetic acid and benzoic acid, that would be found in many acidified food products. We determined a variety of safe processing conditions acidified foods with acetic and/or benzoic acid that can be used to to assure the destruction of vegetetative bacterial pathogens in dressings, mayonanaises, and pickled vegetable products that are not heat processed. We determined the times needed to achieve a 5-log reduction of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes for acidified vegetable and dressing products at pH 3.5 and 3.8. These data showed the efficacy of benzoic acid for reducing the time necessary to achieve a 5-log reduction in target pathogens and may be useful for supporting process filings and the determination of critical controls for the manufacture of acidified foods. The data support process filings fressings, mayonnaises, picked vegetables, and other products, which will help companies meet FSMA requirements. Publications related to this project were listed the 108 annual report.


Last Modified: 10/26/2014
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