Study of the suitability of the central composite design to predict the inactivation kinetics by pulsed electric fields (PEF) in Escherichia coli, Staphylococcus aureus and Pseudomonas fluorescens in milk

The kinetics of inactivation of Escherichia coli K12, Staphylococcus aureus and Pseudomonas fluorescens due to pulsed electric fields (PEF) was investigated in the present study. The effects of treatment inlet temperature (20-45 C), electric field strength (EFS; 20-42.5 kV/cm) and treatment time (68-170 μs, as a function of the flow rate) on microbial inactivation were studied with a central composite design using a response surface model (ccRSM). Reductions of 5 and 5.2 log₁₀ cycles were achieved for E. coli and S. aureus, respectively, at 32.5 C, 40 kV/cm and 89 μs. Viability of P. fluorescens was reduced by 5.3 log₁₀ cycles at 32.5 C, but at slightly higher EFS (42.5 kV/cm) and a longer treatment time (106 μs). Statistical models describing microbial inactivation by PEF (R² ≥ 0.91) were derived from the design. The study of the sum of square values after regression analysis showed that EFS was the factor with greatest effect on microbial inactivation. The present study confirms the suitability of using ccRSM as a tool for investigating and predicting microbial inactivation.