doi:10.1016/j.jfoodeng.2004.06.001
Copyright © 2004 Elsevier Ltd All rights reserved.
Effects of pulse polarity and pulse delaying time on pulsed electric fields-induced pasteurization of E. coli O157:H7
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G. Akdemir Evrendileka,
,
and Q.H. Zhangb
aDepartment of Food Engineering, Faculty of Agriculture, Mustafa Kemal University, Tayfur Sokmen Campus, 31034 Alahan-Hatay, Turkey
bDepartment of Food Science and Technology, The Ohio State University, 2015 Fyffe Road Columbus, OH 43210, USA
Received 28 March 2003;
revised 13 February 2004;
accepted 2 June 2004.
Available online 20 August 2004.
Abstract
Effects of pulse polarity and pulse delaying time on inactivation of E. coli O157:H7 inoculated into apple juice and skim milk samples were determined. Inactivation effect was observed as inoculated food samples were subjected to mono and bipolar square wave pulses. Bipolar pulses with different pulse delaying times were also applied. There was no significant difference between mono (2.56 log10 cfu/ml) and bipolar (2.63 log10 cfu/ml) pulses on the inactivation of E. coli O157:H7 inoculated into apple juice (P > 0.05). However, results in skim milk yielded a significant difference between mono (1.27 log10 cfu/ml) and bipolar (1.96 log10 cfu/ml) pulses with bipolar pulses being significantly more efficient (P < 0.05). Among different pulse delaying times, 20 μs caused a significantly higher inactivation than the others (P < 0.05) in apple juice and skim milk.
Keywords: Microbial inactivation; PEF; Pulse polarity; Pulse delaying time
Fig. 1. (a) Circuit diagram of a laboratory-scale high voltage pulse generator (OSU-4A). Rc refers to the charging resistor, V refers to a power supplier, and C1 refer to the capacitor. U1, U2, U3 and U4 refer to switch 1, switch 2, switch 3 and switch 4, respectively. (b) System diagram of a laboratory-scale high voltage pulse generator (OSU-4A).
Fig. 2. Diagrammatic drawing of co-field flow treatment chambers for OSU-4 PEF systems.
Fig. 3. Configuration of the OSU-4A pulsed electric field system.
Fig. 4. (a) Square wave bipolar pulse, (b) square wave monopolar pulse.
Fig. 5. Inactivation of E. coli O157:H7 by different pulse polarity in apple juice. Pulse delaying time was 20 μs.
Fig. 6. Inactivation of E. coli O157:H7 by different pulse polarity in skim milk samples. Pulse delaying time was 20 μs.
Fig. 7. The effect of pulse delay time on the inactivation of E. coli O157:H7 in apple juice samples.
Fig. 8. The effect of pulse delay time on the inactivation of E. coli O157:H7 in skim milk samples.
Table 1.
PEF treatment parameters used for apple juice and skim milk


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