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

Pea soup inoculated with 10(7) CFU/mL of Escherichia coli, Bacillus su btilis, or a mixture of the two organisms was treated with pulsed elec tric 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 ra te in a continuous treatment chamber. Two passes were selected to reac h 20 or 30 pulses under selected conditions. Inactivation of Escherich ia coli and Bacillus subtilis suspended in pea soup increased with inc reases in intensity of the electric field, number of pulses, and pulsi ng 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 microorg anism alone. Meanwhile, reductions of up to 4.8D were observed when th e 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 inocul ated with a mixture of the microorganisms and exposed to PEF greater t han 30 kV/cm and bulk temperatures over 53C exhibited inactivation gre ater than 2.0D while less than 1.6D was observed when the temperature was below 53C.