Location: Food Science Research
2012 Annual Report
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.
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.
The pending implementation of the Food Safety Modernization Act has led to new research to fill knowledge gaps that exist in determining how to achieve a 5-log reduction for acidified foods for products having pH and acid conditions outside of published safe processing parameters. Examples include thermal processing at pH values above pH 4.1 (at or below pH 4.6), and non-thermal processes (cold-fill products) for pH 3.5 or lower. There is also concern about the need to kill bacillus spores to prevent their germination and growth, with concomitant pH rise, in acidified vegetable products having a pH between 4.1 and pH 4.6. To aid industry to develop safe processing parameters, and to aid the Food and Drug Administration (FDA) in the development of science based regulations, we have conducted research to fill these knowledge gaps. Our research has defined the processing parameters for thermal processes and cold fill products based on the 5-log reduction standard for the conditions described above. We have shown that Escherichia coli O157:H7 and related serotypes are the principal organisms of concern in acidified products, and these bacteria are more heat and acid resistant than Salmonella or Listeria. We have also found that deamination of specific amino acids by vegetative bacilli can result in a pH increase in acidified vegetables, but anaerobic conditions and buffering are significant barriers to spore germination, growth and pH increase. This work meets the overall objective of the project to aid the FDA in assessing the safety of non-heat treated acidified foods and help the industry to design safe acidified foods products.