INACTIVATION OF ESCHERICHIA COLI AND BACILLUS SUBTILIS SUSPENDED IN PEA SOUP USING PULSED ELECTRIC FIELDS

Pea soup inoculated with 10⁷ CFU/mL of Escherichia coli, Bacillus subtilis, or a mixture of the two organisms was treated with pulsed electric fields (PEF) of selected intensities of 25, 28, 30, and 33 kV/cm. The pulsing rate was adjusted to 2.9, 4.3, or 6.7 Hz to achieve 10 or 15 pulses per pass while using either 0.5 L/min or 0.75 L/min flow rate in a continuous treatment chamber. Two passes were selected to reach 20 or 30 pulses under selected conditions. Inactivation of Escherichia coli and Bacillus subtilis suspended in pea soup increased with increases in intensity of the electric field, number of pulses, and pulsing rate. A reduction of 6.5D was obtained at 33 kV/cm, 0.5 L/min, 4.3 Hz, and 30 pulses with E. coli and 5.3D for B. subtilis, each microorganism alone. Meanwhile, reductions of up to 4.8D were observed when the pea soup containing a mixture of the microorganisms was treated with PEF of 30 kV/cm at 6.7 Hz and 0.75 L/min. In general, pea soup inoculated with a mixture of the microorganisms and exposed to PEF greater than 30 kV/cm and bulk temperatures over 53C exhibited inactivation greater than 2.0D while less than 1.6D was observed when the temperature was below 53C.