Kill-step validation for the baking process
In September, FDA issued the final rule for preventive controls for human food as part of the Food Safety Modernization Act (FSMA). As expected, validation that the baking process provides a kill step for pathogens was part of the rule.
Nearly two years ago, AIB International, Manhattan, KS, initiated a kill-step validation study for bakery products to help meet this FSMA requirement. Conducted in collaboration with the American Bakers Association Food Technical Regulatory Affairs Committee, Kansas State University and the University of Nebraska-Lincoln, the initial study on hamburger buns helped establish foundational procedures for the baking industry to address kill-step validation. The purpose of this single study was to validate―in a controlled research setting―that hamburger bun dough inoculated with specific organisms and baked under typical conditions delivers the desired lethality to these organisms.
To meet FSMA validation requirement §117.160(b)(2) requires, in part, that “the validation of preventive controls include collecting and evaluating scientific and technical information or, when such information is not available or is insufficient, conducting studies to determine whether the preventive controls, when properly implemented, will effectively control the hazards that are reasonably likely to occur.” The AIB study employed a straightforward approach of using internal product temperature as measured with temperature probes during the baking process.
The study was conducted in a Biosafety Level 2 lab under strictly controlled conditions. Wheat flour was inoculated with several strains of Salmonella, some known for their high heat resistance, at levels that would allow for confirmation of multiple log reductions of colony-forming units (CFU) in the final baked product. This flour was then used to make dough for hamburger buns using common industry processes. Internal temperature was recorded throughout the baking cycle. Buns were sampled throughout the baking process, as well as after baking.
Results showed that a 5-log reduction, a threshold that FDA has used in other food industry segments, was achieved at about half the time to bake a quality bun. By the end of the bake, the log reduction was in the thousands.
Additional testing in this project, along with the time-temperature baking profile, determined the D-value (time required at a certain temperature to reduce the bacterial load by 1 log), Z-value (change in temperature required to reduce a certain bacterial load by 1 log), and thermal death time (the shortest time needed to kill all organisms at a specific temperature under defined conditions) for the Salmonella organisms in the hamburger bun baking process. With all this information, a relationship could be made between the internal product temperature and the log reduction of potential pathogens that may be present in the unbaked dough. The final step was to develop a simple spreadsheet calculator that would combine production data on internal temperature with the determined D- and Z-values to generate graphs for cumulative and total log reduction of a specific baking process.
In practical terms, lethality of the target organisms begins at about 120°F and is complete at about 170°F. The typical hamburger bun baking process achieves an internal temperature of about 200°F to achieve basic finished product quality parameters of internal crumb structure, product volume/size and crust color. Applying the time/temperature model developed through this study easily validates that the typical baking profile is a kill step and meets FSMA regulation requirements. Further, gathering data on the internal temperature of bakery products is a common practice in many bakeries to monitor product quality, consistency and efficiency of the oven operation. Existing data could be used through the model to demonstrate kill-step validation.
Additional studies are underway for multigrain pan bread, muffins and cookies. AIB aims to provide calculators for a range of bakery products to determine how attributes influence the heat resistance of microorganisms of interest to the baking industry.
To access the latest work on these kill-step calculators, visit "Baking Process Kill Step Calculators" on the AIB International website.