Dr. Bradley Marks leads an interdisciplinary research team focused on food safety engineering, particularly microbial inactivation modeling and improving methods for validating pasteurization processes for ready-to-eat foods, particularly for low-moisture foods and meat/poultry products. His research program has been continuously funded by competitive federal grants for over 23 years, in addition to numerous funded projects and partnerships with industry associations and individual companies. Dr. Marks has received numerous teaching awards, at the department, university, and national level. He has served as the Biosystems Engineering Undergraduate Program Coordinator for more than 13 years, and has led the program through three highly successful ABET review cycles.
Industry Expertise (5)
Health and Wellness
Writing and Editing
Areas of Expertise (5)
Food Safety Engineering
Food Safety and Engineering
Microbial Inactivation Modeling
Purdue University: Ph.D.
Purdue University: M.S.
Michigan State University: B.S.
Journal Articles (3)
Impact of Process Temperature, Humidity, and Initial Product Moisture on Thermal Inactivation of Salmonella Enteritidis PT 30 on Pistachios during Hot-Air HeatingJournal of Food Protection
Kaitlyn Casulli, Francisco Garcés Vega, Kirk D. Dolan, Elliot T. Ryser, Linda J Harris, Bradley P. Marks
2018 Some thermal processes, such as pistachio roasting, are not yet well characterized with respect to the impact of product and process variables on Salmonella lethality. This study aimed to quantify the effects of process temperature, humidity, and initial product water activity (aw), on Salmonella lethality for in-shell pistachios. In-shell pistachios were inoculated with Salmonella Enteritidis PT 30 (∼8.5 log CFU/g), equilibrated (0.45 or 0.65 aw), and heated without soaking ("dry") or after a pure-water or 27% NaCl brining pretreatment ("presoaked"). Inoculated pistachio samples (15 g) were heated in a laboratory-scale, moist-air convection oven at 104.4 or 118.3°C, humidities of ∼3, 15, or 30%, v/v (∼24.4, 54.4, or 69.4°C dew point), and air speed of 1.3 m/s. Salmonella survivors were quantified at six times during each treatment, targeting total reductions of ∼3 to 5 log. Survivor data were analyzed using analysis of variance to identify main effects (time, temperature, humidity, and initial aw) and two-term interactions with time. As expected, lethality increased ( P < 0.05) with temperature and humidity. For example, the time to achieve a 4-log reduction decreased 50 to 80% when humidity increased from ∼3 to 30%. When the dry and presoaked treatments were analyzed separately, initial product aw (0.45 versus 0.65 aw or 0.75 versus 0.95 aw) did not affect lethality ( P > 0.05). However, when comparing dry against presoaked treatments, the time to achieve a 4-log reduction decreased 55 to 85% ( P < 0.05) for presoaked pistachios subjected to the same temperature-humidity treatment. Salt had no effect ( P > 0.05) on lethality outcomes. These results, relative to initial aw, process humidity, brining, and salt effects on process lethality, are critically important and must be considered in the design and validation of thermal processes for Salmonella reduction in pistachio processing.
Modeling and Statistical Issues Related to Salmonella in Low Water Activity FoodsControl of Salmonella and Other Bacterial Pathogens in Low Moisture Foods
Sofia M Santillana Farakos, Michelle Danyluk, Donald Schaffner, Bradley P. Marks
2017 This chapter provides an introduction to modeling Salmonella in low water activity foods focusing on the statistical issues related with model development and the development of a quantitative microbial risk assessment (QMRA). Salmonella on peanuts are used in an example case study. Predictive models in food microbiology are used to estimate microbial concentration levels given certain conditions. The chapter show a case study on how to develop a primary and secondary predictive model for survival of Salmonella using the data collected by Brar et al. on Salmonella survival on raw peanuts at three different temperatures (-24, 4, and 22°C). This approach could be used for survival data on any pathogen in any food, and is explored for survival of Salmonella in low water activity foods. Survival of Salmonella in low water activity foods may be characterized by curves with a relatively rapid initial decline followed by long-term persistence, with little decline over time.
Inoculation Protocols Influence the Thermal Resistance of Salmonella Enteritidis PT 30 in Fabricated Almond, Wheat, and Date ProductsJournal of Food Protection
Pichamon Limcharoenchat, Sarah E. Buchholz, Michael K. James, Nicole O. Hall, Elliot T Ryser, Bradley P. Marks
2018 Inoculation methods in pathogen inactivation studies ideally represent conditions that might occur in real-world scenarios. Surface contamination in or on low-moisture foods affects Salmonella thermal resistance, which is critically important for process validation applications. The objective of this study was to quantify the effect of inoculation protocol on the thermal resistance of Salmonella Enteritidis PT 30 in fabricated low-moisture foods. Almond meal, almond butter, wheat meal, wheat flour, and date paste were inoculated via prefabrication and postfabrication protocols. In the prefabrication protocol, kernels and fruits were surface inoculated and equilibrated to a target water activity (aw) (0.40 for almond and wheat products, 0.45 for date products) before fabricating meal, butter, flour, or paste and then reequilibrating the samples to the target aw. In the postfabrication protocol, meal, butter, flour, and paste were fabricated before inoculation and equilibration. All inoculated and equilibrated samples were subjected to isothermal treatment (80°C), pulled sequentially during processing, cooled, serially diluted, and plated to enumerate survivors. Log-linear and Weibull-type models were fit to the Salmonella survivor data and were compared via the corrected Akaike information criterion. Pre- and postfabrication protocols resulted in significant differences ( P < 0.05) in Salmonella thermal resistance in all products. Overall, the thermal resistance of Salmonella Enteritidis PT 30 in almond products was greater ( P < 0.05) than in wheat products, which was also greater ( P < 0.05) than in date paste. Additionally, Salmonella was more thermally resistant in almond products and date paste when inoculated pre- rather than postfabrication; however, the opposite was true for wheat products. These results indicate that the means of inoculation can significantly affect thermal resistance of Salmonella in low-moisture foods.