Thermal resistance of Salmonella enterica, Escherichia coli and Staphylococcus aureus isolated from vegetable feed ingredients

BACKGROUND: Cattle feed is at the beginning of the food chain in the 'farm-to-fork' model and might serve as a source of contamination with pathogenic bacteria. Heat treatment is one of the most effective methods utilized to ensure the microbial safety of feeds. In this work, the thermal resistance of Salmonella enterica, Escherichia coli and Staphylococcus aureus isolated from vegetable feed ingredients was investigated in phosphate-buffered saline (PBS) and in cattle feed. RESULTS: Mean D values calculated in PBS ranged from 34.08 to 5.70 min at 55 degrees C, decreasing to 0.37 and 0.22 min at 65 degrees C for E. coli and S. enterica, respectively. No relationship was found between thermoresistance and source of isolation. D values in feed were calculated from the adjustment of two nonlinear models to the inactivation data. Thermal resistance of E. coli and S. enterica in cattle feed showed similar results to liquid medium; however, a fivefold increment of S. aureus thermoresistance in feed was observed. Our results also revealed an increase of microbial thermoresistance with the mean feed particle diameter. CONCLUSION: These results provide relevant information for improvement in the safety of cattle feed regarding its process conditions (i.e. time, temperature and particle size). (C) 2013 Society of Chemical Industry