Inactivation of Escherichia coli O157: H7 in liquid whole egg using combined pulsed electric field and thermal treatments (original) (raw)
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Inactivation of Escherichia Coli O157:H7 in Liquid Dialyzed Egg Using Pulsed Electric Fields
Food and Bioproducts Processing, 2004
P ulsed electric field (PEF) pasteurization may be used either to replace or supplement conventional processing of heat-sensitive products such as liquid egg. The objective of this study was to investigate inactivation characteristics of Escherichia coli O157:H7 in liquid egg products at low temperature using square waveform pulsed electric fields. Dialyzed liquid egg products, namely whole egg, egg white and egg yolk, were exposed to an electric field of 15 kV cm À1 at a low temperature of 0 C. The square voltage fields were generated across parallel plate treatment chambers. A pulse frequency of 1 Hz was used. Up to 500 pulses were applied. Product temperature during the PEF treatment was controlled using a water cooling system. About 1, 3 and 3.5 log reductions were obtained for the dialyzed egg white, egg yolk and whole egg products, respectively. The results showed that microbial inactivation rate increased with increasing number of pulses, especially for the egg yolk and whole egg products. The inactivation kinetics was exponential with some tailing. A new kinetic model for the bacteria inactivation was proposed.
Journal of Food Engineering, 2007
The effects of temperature, treatment time and electric field strength on inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in liquid egg yolk by pulsed electric field (PEF) processing were examined using the reaction kinetics approach. Egg yolk, inoculated with 108CFUmLAˋ1ofE.coliO157:H7orS.enteritidis,wastreatedinacontinuousflowprocessat20,30and40°Cincombinationwithpulsedelectricfieldintensitiesof20and30kVcmAˋ1.AbiphasicinstantreversalPEFwaveformwitha2lspulsewidthwasusedandamaximumof105pulseswereapplied.Increasingtheappliedelectricfieldintensity,treatmenttimeandprocesstemperatureresultedinincreasedbacterialinactivation.At30kVcmAˋ1and40°C,thepopulationsofE.coliO157:H7andS.enteritidiswerereducedby10 8 CFU mL À1 of E. coli O157:H7 or S. enteritidis, was treated in a continuous flow process at 20, 30 and 40°C in combination with pulsed electric field intensities of 20 and 30 kV cm À1 . A biphasic instant reversal PEF waveform with a 2 ls pulse width was used and a maximum of 105 pulses were applied. Increasing the applied electric field intensity, treatment time and process temperature resulted in increased bacterial inactivation. At 30 kV cm À1 and 40°C, the populations of E. coli O157:H7 and S. enteritidis were reduced by 108CFUmLAˋ1ofE.coliO157:H7orS.enteritidis,wastreatedinacontinuousflowprocessat20,30and40°Cincombinationwithpulsedelectricfieldintensitiesof20and30kVcmAˋ1.AbiphasicinstantreversalPEFwaveformwitha2lspulsewidthwasusedandamaximumof105pulseswereapplied.Increasingtheappliedelectricfieldintensity,treatmenttimeandprocesstemperatureresultedinincreasedbacterialinactivation.At30kVcmAˋ1and40°C,thepopulationsofE.coliO157:H7andS.enteritidiswerereducedby5 logs. The inactivation rate constants increased from 0.004 to 0.098 l s À1 for S. enteritidis whereas for E. coli O157:H7 the constants increased from 0.009 to 0.039 ls À1 as processing temperature increased from 20 to 40°C. S. enteritidis was more resistant to PEF inactivation than E. coli O157:H7 at lower processing temperatures.
2004, Ottawa, Canada August 1 - 4, 2004, 2004
The effects of temperature, treatment time and electric field strength on inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in liquid egg yolk by pulsed electric field (PEF) processing were examined using the reaction kinetics approach. Egg yolk, inoculated with 108CFUmLAˋ1ofE.coliO157:H7orS.enteritidis,wastreatedinacontinuousflowprocessat20,30and40°Cincombinationwithpulsedelectricfieldintensitiesof20and30kVcmAˋ1.AbiphasicinstantreversalPEFwaveformwitha2lspulsewidthwasusedandamaximumof105pulseswereapplied.Increasingtheappliedelectricfieldintensity,treatmenttimeandprocesstemperatureresultedinincreasedbacterialinactivation.At30kVcmAˋ1and40°C,thepopulationsofE.coliO157:H7andS.enteritidiswerereducedby10 8 CFU mL À1 of E. coli O157:H7 or S. enteritidis, was treated in a continuous flow process at 20, 30 and 40°C in combination with pulsed electric field intensities of 20 and 30 kV cm À1 . A biphasic instant reversal PEF waveform with a 2 ls pulse width was used and a maximum of 105 pulses were applied. Increasing the applied electric field intensity, treatment time and process temperature resulted in increased bacterial inactivation. At 30 kV cm À1 and 40°C, the populations of E. coli O157:H7 and S. enteritidis were reduced by 108CFUmLAˋ1ofE.coliO157:H7orS.enteritidis,wastreatedinacontinuousflowprocessat20,30and40°Cincombinationwithpulsedelectricfieldintensitiesof20and30kVcmAˋ1.AbiphasicinstantreversalPEFwaveformwitha2lspulsewidthwasusedandamaximumof105pulseswereapplied.Increasingtheappliedelectricfieldintensity,treatmenttimeandprocesstemperatureresultedinincreasedbacterialinactivation.At30kVcmAˋ1and40°C,thepopulationsofE.coliO157:H7andS.enteritidiswerereducedby5 logs. The inactivation rate constants increased from 0.004 to 0.098 l s À1 for S. enteritidis whereas for E. coli O157:H7 the constants increased from 0.009 to 0.039 ls À1 as processing temperature increased from 20 to 40°C. S. enteritidis was more resistant to PEF inactivation than E. coli O157:H7 at lower processing temperatures.
INACTIVATION OF ESCHERICHIA COLI SUSPENDED IN LIQUID EGG USING PULSED ELECTRIC FIELDS
Journal of Food Processing and Preservation, 1997
Liquid egg inoculated with Escherichia coli was exposed to a 26kV/cm pulsed electric field with 2 and 4 μs pulse duration, 1.25 and 2.50 Hz pulsing rates, up to 100 pulses/unit volume, and stepwise and continuous recirculation treatment schemes while maintaining a bulk temperature below 37C. The inactivation of E. coli was a function of the pulse duration and the number of pulses. The destruction of Escherichia coli in liquid egg followed a first order kinetic and the treatment was more effective when the applied pulses were of a 4 μs pulse duration. A 6D reduction was obtained for viable E. coli using both pulsing rates and treatment schemes with no protein coagulation.
Journal of Food Protection, 2003
This investigation was undertaken to study the inactivation of Escherichia coli O157:H7 by pulsed electric field (PEF) treatment and heat treatment after exposure to different stresses. E. coli O157:H7 cells exposed to different pHs (3.6, 5.2, and 7.0 for 6 h), different temperatures (4, 35, and 40°C for 6 h), and different pre-PEF treatments (10, 15, and 20 kV/cm) were treated with PEFs (20, 25, and 30 kV/cm) or heat (60°C for 3 min). The results of these experiments demonstrated that a pH of 3.6 and temperatures of 4 and 40°C caused significant decreases in the inactivation of E. coli O157:H7 by PEF treatment and heat treatment (P < 0.05). Pre-PEF treatments, pHs of 5.2 and 7.0, and a temperature of 35°C, on the other hand, did not result in any resistance of E. coli O157:H7 cells to inactivation by PEF treatment and heat treatment (P > 0.05).
Food Microbiology, 2002
The inactivation of Escherichia coli O157:H7 by pulsed electric ¢eld (PEF) processing as a function of electric ¢eld strength (15^30 kVcm À1), pulse number (1^20), temperature (5^651C) and pH (3?5 and 6?8) was studied using a commercially available pulser, a static chamber and gellan gum gel as a suspension medium.The custom-designed static chamber achieved near-isothermal treatment conditions while eliminating £ow ¢eld e¡ects. Gellan gum gel was used to suspend the bacteria for treatment. It allowed uniform distribution of bacteria and neither inhibited nor promoted bacterial growth.The combination of equipment design and experimental protocol allowed the contribution of electrical (PEF) and thermal energy to be measured separately. In water-based gel, a maximum of 3 log reductions were achieved by PEF energy. Greater inactivation was observed at a treatment temperature of 55 o C, but the additional inactivation was attributable entirely to thermal energy. Microbial injury was also observed at this temperature. At 60 o C and above, complete inactivation was achieved, but this was attributable entirely to thermal energy. In water-based gellan gum gel adjusted to pH 3?5, again a 3 log reduction was achieved by PEF. In gel made from freshly squeezed apple juice naturally having the same pH, however, a maximum of 1?5 log reduction was observed.
International Journal of Food Science and Technology, 2009
Pulsed electric field (PEF) exposes a fluid or semi-fluid product to short pulses of high-energy electricity, which can inactivate microorganisms. The efficacy of PEF treatment for pasteurisation of liquid eggs may be a function of processing temperature. In this study, effects of PEF, temperature, pH and PEF with mild heat (PEF + heat) on the inactivation of Salmonella typhimurium DT104 cells in liquid whole egg (LWE) were investigated. Cells of S. typhimurium were inoculated into LWE pH adjusted to 6.6, 7.2 or 8.2 at 15, 25, 30 and 40 °C. The PEF field strength, pulse duration and total treatment time were 25 kV cm−1, 2.1 μs and 250 μs respectively. Cells of S. typhimurium in LWE at pH 7.2 were reduced by 2.1 logs at 40 °C and 1.8 logs at 30 °C. The PEF inactivation of S. typhimurium cells at 15 or 25 °C was pH dependent. Heat treatment at 55 °C for 3.5 min or PEF treatment at 20 °C resulted in c. 1-log reduction of S. typhimurium cells. Combination of PEF + 55 °C achieved 3-log reduction of S. typhimurium cells and was comparable to the inactivation by the heat treatment at 60 °C for 3.5 min. With further development, PEF + heat treatment may have an advantage over high-temperature treatment for pasteurisation of liquid eggs.
Innovative Food Science & Emerging Technologies, 2010
In this study, the lethal effectiveness of pulsed electric fields (PEF) on the inactivation of Salmonella enterica subs. enterica ser. Typhimurium and Staphylococcus aureus in liquid whole egg (LWE) has been investigated. Maximum inactivation levels of 4 and 3 Log 10 cycles of the population of Salmonella Typhimurium and S. aureus were achieved with treatments of 45 kV/cm, 30 μs and 419 kJ/kg, and 40 kV/cm for 15 μs and 166 kJ/ kg, respectively. The non-linear kinetics of inactivation observed for both microorganisms at all the investigated electric field strengths were described by mathematical equations based on the Weibull distribution. The developed equations enabled to compare the microbial resistance to PEF and to establish the most suitable treatment conditions to achieve a determined level of microbial inactivation. PEF treatments varying from 30 kV/cm, 67 µs and 393 kJ/kg to 45 kV/cm, 19 µs and 285 kJ/kg allow to reduce 3 Log 10 cycles the population of the microorganism of concern in PEF food processing of LWE, Salmonella Typhimurium. Industrial relevance: The data presented in this investigation in terms of electric field strength, specific energy and treatment time result of relevance to evaluate the possibilities of PEF technology to pasteurize LWE with this technology. The models developed in this study can be applied to engineering design, and for the evaluation and optimization of the PEF technology as a new technique to obtain Salmonella free LWE. Based on our results it is not recommended to apply treatments of energy levels higher than 250 kJ/kg, since PEF lethality hardly increased but markedly augmented the energetic costs. For these energy values, PEF technology by itself is not sufficient (3 Log10 cycles in the best case scenario) to assure the safe security of LWE. Therefore, intelligent combinations of PEF with other preservation technologies have to be developed in order to use pulsed electric fields as an alternative to heat pasteurization of LWE.
2010
The aim of this work was to study the efficiency of inactivation of Escherichia coli cells in aqueous suspensions using combined moderate pulsed electric field (PEF) and thermal treatments. The inactivation kinetics of E. coli cells in aqueous suspensions (1 wt%) was monitored using conductometric technique. The electric field strength E was within 5-7.5 kV/cm, the effective PEF treatment time PEF t was within 0-0.75 s, the pulse duration t i was within 0.3-1 ms, the medium temperature was 30-50°C, and the time of thermal treatment t T was within 0-7000 s. The organic acid concentration was within 0-0.5 g/L.The damage of E. coli was accompanied by release of intracellular components. The synergy between the PEF and thermal treatments in E. coli inactivation was clearly demonstrated. The damage efficiency was noticeably improved by addition of organic acids, especially lactic acid.
Food Research International, 1995
Inactivation of microorganisms exposed to high-voltage pulsed electric fields is a promising non-thermal food preservation technology. This paper demonstrates and validates the inactivation of Escherichia coli, a Gram-negative bacterium and Staphylococcus aureus, a Gram-positive bacterium, subjected to high-voltage electric field pulses. A four-log cycle reduction in microbial population is achieved in model foods such as simulated milk ultrafiltrate (SMUF) with a peak electric field strength of 16 kV/cm and 60 pulses with a pulse width ranging between 200 and 300 μs. The temperature of the cell suspension was kept below the lethal temperature, demonstrating that inactivation is not due to thermal effects induced by the pulses of high-voltage electricity. Thermal food preservation causes undesirable changes in the physical character, quality and nutrient content of foods. Non-thermal preservation techniques minimize the undesirable changes in foods. A comparison between the inactivation of microorganisms by high-voltage pulsed electric fields and thermal methods of food preservation is also discussed.