INACTIVATION of E. COLI FOR FOOD PASTEURIZATION BY HIGH-STRENGTH PULSED ELECTRIC FIELDS

Abstract

Pulsed electric fields of very high field strength and short duration are effective in the inactivation of E. coli. Nine log reduction in E. coli viability was achieved using a stepwise pulsed electric field treatment where E. coli suspensions were treated repeatedly in batches. It was demonstrated that high-strength pulsed electric field treatment is adequate for pasteurization of liquid foods. A 40,000 volt pulse generator was constructed to supply high voltage electric pulses to a treatment chamber with two parallel plate stainless steel electrodes where fluid food was contained. the gap between electrodes was 0.51 cm and the chamber volume was 14 ml. Pulse electric field strength ranged from 35 to 70 kV/cm. Pulse width was selected at 2 μs. Number of pulses per treatment varied from 1 to 80. E. coli were suspended in a simulated milk ultra-filtrate (SMUF) and treated with pulsed electric fields in a batch mode. the suspension fluid was maintained at constant temperatures of 7, 20, or 33C. Maximum temperature change occurring during each pulse was 0.3C measured by a fiber optics temperature probe. E. coli viability before and after treatment were assayed by counting colony forming units (cfu).