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United States Department of Agriculture

Agricultural Research Service


Location: Residue Chemistry and Predictive Microbiology

2011 Annual Report

1a.Objectives (from AD-416)
To evaluate, validate, and where necessary, develop new innovative, robust and valid predictive models for the responses of microbial pathogens, including foodborne threat agents, in select food matrices, as a function of: temperature, food formulation, competitive microflora, physiological history, and surface transfer. To develop novel approaches to assess model performance and robustness, leading to more efficient strategies for producing and extrapolating models to different classes of food. To determine the probability distribution of lag phase duration (LPD) for foodborne pathogens, as a function of the previous bacterial physiological history, to allow risk managers to estimate worst-and best-case scenarios for pathogen behavior, depending on likely sources of contamination; To identify molecular markers that discriminate bacterial lag, growth and stationary phases, thus leading to more mechanistic models and greater certainty for LPD prediction.

1b.Approach (from AD-416)
Quantitative data will be collected for the effects of selected environmental parameters on foodborne pathogen growth, survival and inactivation. Relevant environmental conditions will include food formulation, native microbial flora, inoculum level, bacterial history, and the effects of food process operations. Priority pathogen-food combinations will be identified through stakeholder interactions and by identifying sensitive data gaps in microbial risk assessment. Experimental data will be used to confirm and where necessary produce primary growth and inactivation models, as well as probabilistic models for growth/no growth interfaces and microbial transfer among food processing surfaces. Model performance will be described using independent validation data from ongoing experiments with food matrices and microbiology databases such as ComBase. The resulting technologies will be transferred to stakeholders vis the ARS Pathogen Modeling Program and process risk model software.

3.Progress Report
Experiments examining the growth of L. monocytogenes, E. coli O157:H7, and Salmonella spp. as affected by sodium lactate and storage temperature in ready-to-eat ham and growth probability of E. coli O157:H7 as affected by salt, sodium pyrophosphate and sodium lactate in ground beef were completed. Experiments on surface decontamination and growth of L. monocytogenes, E. coli O157:H7, and Salmonella spp. with lactic acid, sodium lactate and diacetate on ready-to-eat meat is in progress.

A series of experiments were conducted to determine the germination and outgrowth of Clostridium perfringens spores during cooling of cooked pork products. Finally, predictive model for growth of Clostridium perfringens during cooling of cooked products based on the product composition factors is being developed. The growth data/predictive model on the safe cooling rate of meat will enable the food industry to assure that cooked products remain pathogen-free.

Research was conducted to develop predictive models for non-O157 Shiga toxin-producing E. coli (STEC) in ground beef and spinach. A cocktail of different strains was inoculated in ground beef and spinach and incubated at different temperatures to develop growth curves. The growth curves were analyzed for developing mathematical models.

Research was also conducted to investigate the effect of temperature on the growth of microorganisms. As a result of this research, a new empirical mathematical model that can more realistically describe the relationship between temperature and bacterial growth rate was established and validated. Further, this research led to the development of a thermodynamic model that is based on the Arrhenius equation. This is a new mathematical model that can accurately evaluate the effect of temperature on bacterial growth.

The research is related to 2006-2010 NP 108 Action Plan Sections 1.2.7 (Risk Assessment) and 1.2.9 (Food Security). The research work addresses the objectives of producing improved Quantitative Microbial Risk Assessment through more accurate exposure assessment and risk characterization, robust and validated process risk models that address hazards in complex food matrices, and validated models that predict the effect of specific intervention strategies on threat agents.

1. Adequate cooking, cooling, and proper product formulation ensure safety against pathogens in cooked food products while minimizing quality losses. ARS researchers at Wyndmoor, PA, conducted research to develop mathematical models for describing the effect of cooking temperatures (55 to 71°C) and antimicrobial agents (such as cinnamaldehyde and carvacrol) on inactivation of Salmonella in ground chicken, the impact of product formulation (salt, sodium pyrophosphate and sodium lactate) on survival of E. coli O157:H7 in beef, and the difference in cooling rates on the germination and outgrowth of Clostridium perfringens spores in cooked beef. These models will assist food processors in designing cooking and cooling processes for the production of safe chicken and beef products with extended shelf life, and help the manufacturers to select product formulations that enhance the safety and quality of raw and cooked meat products during distribution and storage.

Review Publications
Hwang, C., Sheen, S. 2011. Growth characteristics of Listeria monocytogenes as affected by a -native microflora in cooked ham under refrigerated and temperature abuse conditions. Food Microbiology. 28:350-355.

Oscar, T.P. 2011. Development and validation of a predictive model for survival and growth of Salmonella on chicken skin stored at 4 to 12 deg C. Journal of Food Protection. 74(2):279-284.

Juneja, V.K., Marks, H.M., Huang, L., Thippareddi, H. 2011. Predictive model for growth of Clostridium perfringens during cooling of cooked uncured meat and poultry. Food Microbiology. 28:791-795.

Grosulescu, C., Ravishankar, S., Juneja, V.K. 2011. Effects and interactions of sodium lactate, sodium diacetate, and pediocin on the thermal inactivation of starved cells of Listeria monocytogenes on the surface of bologna. Food Microbiology. 28:440-446.

Bhaduri, S., Chaney, K.J., Smith, J.L. 2011. A procedure for monitoring the presence of the virulence plasmid (pYV) in Yersinia pestis under culture conditions. Foodborne Pathogens and Disease. 8:459-463.

Bhaduri, S. 2011. Effect of salt and acidic pH on the stability of virulence plasmid (pYV) in Yersinia enterocolitica and expression of virulence-associated characteristics. Food Microbiology. 28:171-173.

Hwang, C., Juneja, V.K. 2011. The effects of salt, sodium pyrophosphate and sodium lactate on the probability of growth of Escherichia coli O157:H7 in ground beef. Journal of Food Protection. 74(4):622-626.

Last Modified: 4/18/2014
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