Applying microbial predictive and machine learning model data to evaluate thermal inactivation of salmonella and the surrogate enterococcus faecium in reconstructed ground chicken meat affected by temperature and salt concentrations

This study was to model the thermal inactivation of Salmonella and the surrogate Enterococcus faecium in reconstructed ground chicken meat as affected by temperatures and salt concentrations. Fresh chicken breast was ground, inoculated with nalidixic-acid (NaL-100 ppm) resistant S. Typhimurium or E. faecium followed by the addition of NaCl (0, 1.0, 3.0 or 5.0 %) + Na-tripolyphosphate (0.5 %) solutions to achieve 8 % pump rate. Samples (10 g) were placed into filtered food sample bags, vacuum packaged and stored at 4°C for 42-h before heating in a circulated water bath at 62, 66, 70, and 74°C for 0 to 240 s, respectively. Surviving cells were enumerated on NaL-tryptic soy agars. Microbial populations and d-values [n = 6, Global-Fit and United States Department of Agriculture (USDA)-Integrated-Predictive-Modeling-Program software] were analyzed by R-software (orthogonal polynomial model). Machine learning (ML) models including Random Forest, Support Vector, and Bayesian Ridge Regressions were used to predict microbial inhibition under various thermal and salt treatments. Thermal dynamic data fit Weibull Model (RMSE=0.48 to 0.71), but not the linear model (RMSE >1.000). Salt (3 and 5 % vs 0 %) significantly (P < 0.05) increased the thermal resistance of S. Typhimurium (reduction:1.02 vs 1.86 log₁₀CFU/g) when heated at 62°C whereas when the heating temperature increased to 74°C the pathogen cells become more vulnerable (reduction: 3.04-4.44 vs 1.63 log₁₀CFU/g). E. faecium were resistant to heat compared to Salmonella as shown by fewer reductions (1.02-4.44 vs 4.61-6.94 log₁₀CFU/g) and higher (P < 0.05) d-values in all tested samples. ML models suggested that heating temperature was the most important predictor of cell reduction, followed by exposure time and salt concentrations. E. faecium is a promising pathogen surrogate could be used in thermal inactivation validation studies. These results will be useful for the poultry meat industry to develop proper thermal processes for control of pathogen in chicken products.