Short communicationEfficacy of pulsed electric fields for the inactivation of indicator microorganisms and foodborne pathogens in liquids and raw chicken
Introduction
There are an estimated 9 million cases of human Campylobacteriosis per year in the European Union (EFSA, 2011). While a large proportion of Campylobacter infections are attributed to the handling, preparation and consumption of chicken meat, contaminated water and milk have also been implicated as sources of infection (Danis et al., 2009, Fahey et al., 1995, Heuvelink et al., 2008, Mosqueda-Melgar et al., 2008, Oliveira et al., 2005). Pulsed electric fields (PEF) is a non-thermal decontamination treatment which has been shown to be lethal to many pathogenic and spoilage bacteria (Alvarez et al., 2003, Amiali et al., 2007, Grahl and Markl, 1996, Mosqueda-Melgar et al., 2008, Wan et al., 2009). It has also demonstrated great potential as an alternative to conventional thermal pasteurisation for milk (Walkling-Ribeiro, Noci, Cronin, Lyng, & Morgan, 2008). PEF treatment generally involves the application of short pulses (1–100 μs) of high voltage electric fields (10–80 kV/cm) to foods flowing through or placed between two electrodes (Gongora-Nieto, Pedrow, Swanson, & Barbosa-Cánovas, 2004). The application of an external electric field to biological cells induces an electrical potential across the cell membrane which, when exceeding critical levels, leads to an electrical breakdown and local structural changes to the cell membrane (Heinz, Toepfl, & Knorr, 2003). While numerous studies have investigated PEF for the inactivation of foodborne bacteria such as Escherichia coli and Salmonella spp. (Danis et al., 2009, Mosqueda-Melgar et al., 2008), there is only a single published study which has examined the application of PEF technology for the inactivation of Campylobacter (Sagarzazu, Cebrián, Pagán, Condón, & Mañas, 2010).
Thus far, data published on PEF technology suggest its ability to inactivate microorganisms is more suited to liquid and semi-solid foods while its application to solid foods is thought to be mainly suited to the extraction of components or the acceleration of certain processes (i.e. marination or curing of meat) (Mosqueda-Melgar et al., 2008, Raso and Heinz, 2006, Toepfl et al., 2007). However, the authors are unaware of any studies which have investigated the potential of PEF for the decontamination of solid foods such as chicken. There is growing interest in exploring and identifying technologies that could reduce contamination of chicken carcasses as risk assessment studies predict that reducing the microbial load on carcasses can result in a significant reduction in the incidence of gastroenteritis in humans (Havelaar et al., 2007, Loretz et al., 2009). Current physical decontamination methods such as hot water immersion or steam pasteurisation can reduce numbers of Campylobacter on carcases by up to 1.9 or 1.3 log10 CFU/g, respectively, although these thermal treatments may have a negative impact on the appearance of broiler skin (James et al., 2007, Whyte et al., 2003). PEF is a potential alternative technology though its effectiveness for microbial decontamination of poultry has not been studied. In particular, its effectiveness towards Campylobacter needs to be investigated given the public health significance of this organism. Therefore, the aims of the present study were (i) to investigate the susceptibility of a number of Campylobacter isolates to PEF treatment in a liquid medium using E. coli ATCC 25922 and Salmonella Enteritidis ATCC 13076 for comparative purposes, and (ii) to assess whether or not PEF treatment had potential for decontaminating raw chicken inoculated with the aforementioned microorganisms.
Section snippets
Microorganisms and culture preparation
A total of ten Campylobacter isolates (7 × Campylobacter jejuni and 3 × Campylobacter coli) were used in the susceptibility studies. The C. coli isolates were 1140 DF, 1662 DF and 2124 GF, while 323 BC, 1135 DF, 1136 DF, 1146 DF, 1147 DF, 1354 DF, NCTC 11168 were C. jejuni. All campylobacters were isolated from retail chicken with the exception of 323 BC, and the typed C. jejuni strain NCTC 11168, both of which are of human clinical origin. All Campylobacter chicken isolates were recovered and
Results and discussion
This study demonstrated that large differences in the susceptibilities of Campylobacter spp to PEF existed which, As can be seen from Table 1, all C. jejuni and C. coli isolates suspended in liquid (1:5 v/v MRD solution) were susceptible to PEF treatments (65 kV/cm, 5 μs, 500 Hz, 10–30 s) with reductions of up to 7.22 log10 CFU/mL achieved for the longest treatment time of 30 s (P < 0.05). In addition, large differences in the susceptibility of isolates were also observed, which, to the
Conculsions
This study showed that Campylobacter are more susceptible to PEF treatment in liquids than E. coli and S. Enterititidis. Furthermore, significant differences in susceptibility to PEF existed between Campylobacter isolates, which has not previously been reported and highlights the importance of strain selection in PEF inactivation studies involving Campylobacter spp. Although the results of this study indicate the unsuitability of PEF for decontaminating raw chicken, it may have a potential
Acknowledgements
Funding for this research was provided under the Irish National Development Plan, through the Food Institutional Research Measure programme administered by the Department of Agriculture, Fisheries and Food.
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