Combined Effects of Microwave Heating and Hydrogen Peroxide on the Destruction of Escherichia Coli

Destruction of Escherichia coli cells was studied in a continuous-flow microwave heating system in combination with low concentrations of hydrogen peroxide (H2O2). The cell suspension was pumped through two helical coils centrally located in two microwave ovens (700 W, 2450 MHz) and heated to selected final temperatures of between 50 and 70 °C. The suspension was then immediately cooled in a condenser connected in series at the exit. To determine the combination effects, H2O2was added separately to the cell suspension at selected concentration levels from 0.05 g/100 g to 0.1g/100 g and immediately subjected to microwave heating. To study the additive effects, the cell suspension was treated with H2O2for 10 min at 24 °C prior to microwave heating. A factorial design of experiments and a response surface analysis were used to evaluate the individual and combined effects of microwave heating and H2O2treatment on the destruction of E. coli. Synergistic effects of microwave heating and H2O2treatment on E. coli destruction were observed and the interaction reached a maximum under exposure of cells to H2O2at 0.075 g/100 g with microwave heating to T=60 °C. When the cell suspensions were subjected to prior H2O2treatment followed by microwave heating, close to additive interaction was found and the highest destruction was achieved with 0.01 g/100 g H2O2when microwave heated at 60 °C.