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This research focuses on developing predictive models for Salmonella Typhimurium and Kentucky on chicken skin stored at 4-12°C, considering factors like low initial dose, microbial competition, and low temperatures. The study includes experimental designs, model development and validation, enumeration methods, and performance evaluation. The findings highlight that microbial competition suppresses growth, and Kentucky strain grows slower. The research contributes to risk assessments in food safety.
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Modeling the Survival and Growth of Salmonella on Chicken Skin Stored at 4 to 12C Thomas P. Oscar, Ph.D. U.S. Department of Agriculture Agricultural Research Service Princess Anne, MD
Introduction • Salmonella & poultry • 1 - 2 cases per 100,000 • Initial contamination • < 30 CFU per chicken carcass • Illness dose • 105 to 107 CFU Int. J. Food Microbiol. 2004. 93:231-247.
Introduction • Risk Assessment • Hazard Identification • Hazard Characterization • Exposure Assessment • Risk Characterization Packaging Contamination Risk Pathway Cold Storage Temp. Abuse Meal Prep. Temp. Abuse Meal Prep. Cross-contamination Cooking Under-cooking Consumption Exposure
Introduction • Predictive microbiology • Support risk assessments • Data gaps • Low initial dose • Microbial competition • Low temperatures
Introduction • Another data gap • Variation among serotypes Autoclaved chicken meat at 25C J. Food Safety. 2000. 20:225-236.
Objective • Develop a predictive model • Survival & growth • Salmonella Typhimurium & Kentucky • Low initial dose (0.9 log) • Chicken thigh skin (2.14 cm2) • with microbial competition • Low temperature (4 to 12C)
Materials & Methods • Experimental design • Model development (Salmonella serotype Typhimurium DT104) • 5 x 5 full factorial • Temperature (4, 6, 8, 10, 12C) • Time (0, 1, 3, 6, 10 days) • 4 replicates
Materials & Methods • Experimental design • Model validation (Salmonella serotype Typhimurium DT104) • 4 x 5 full factorial • Temperature (5, 7, 9, 11C) • Time (0, 1, 3, 6, 10 days) • 2 replicates Interpolation
Materials & Methods • Experimental design • Model validation (Salmonella serotype Kentucky) • 4 x 5 full factorial • Temperature (5, 7, 9, 11C) • Time (0, 1, 3, 6, 10 days) • 2 replicates Extrapolation
Materials & Methods • Salmonella enumeration • Combined MPN & CFU method CFU MPN J. Food Prot. 2006. 69:2048-2057.
Materials & Methods • Plating media • Salmonella serotype Typhimurium DT104 • XLH-CATS • Salmonella serotype Kentucky • XLH-NATS J. Food Prot. 2006. 69:2048-2057.
Materials & Methods • General Regression Neural Network Model ŷ Output (Δ) N(x) D(x) Summation Layer Predicted Value -0.71 … … 4.13 Pattern Layer Distance Function T t Input Layer Temp. time IEEE Trans. Neural. Netw. 1991. 2:568-576
Materials & Methods • Model performance • Residual • Observed - predicted • Acceptable prediction zone (APZ) • -1 log (fail-safe) to 0.5 log (fail-dangerous) • Acceptable performance • 70% of residuals in APZ Prediction bias & accuracy J. Food Sci. 2005. 70:M129-M137.
Results • Salmonella serotype Typhimurium DT104 • Model development (n = 163)
Results • Salmonella serotype Typhimurium DT104 • Model validation for interpolation (n = 77)
Discussion • Salmonella serotype Typhimurium DT104 • Growth on sterile chicken breast meat at 10C Oscar (unpublished)
Results • Salmonella serotype Kentucky • Model validation for extrapolation (n = 70)
Discussion • Variation among serotypes • Kentucky grows slower on chicken skin at 35C J. Food Prot. 2009. 72:2078-2087.
Results & Discussion • Model Performance (Development)
Results & Discussion • Model Performance (Interpolation)
Results & Discussion • Model Performance (Extrapolation)
Conclusions • Model was validated • Microbial competition suppresses growth • MPD = 1 log vs 8 log @ 10C • Kentucky grows slower • Compatible with @Risk
