Effects of pH and temperature on inactivation of Salmonella typhimurium DT104 in liquid whole egg by pulsed electric fields

Abstract

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 ls and 250 ls 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.

Effect of temperature, pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

“…However, in order to avoid the negative effects of heat on sensory and nutritional properties of foods and to answer the increasing consumer's demand for high-quality, minimally processed foods, considerable efforts have been directed toward the development of novel nonthermal processes, such as pulsed electric fields (PEF) (Rajkovic, Smigic, & Devlieghere, 2010, Zwietering, 2002. PEF is a novel processing technology that has been demonstrated to be effective in inactivating different vegetative cells of pathogenic bacteria, including Salmonella Typhimurium STCC 878 and E. coli O157:H7 at temperatures below those used in thermal processing (Amiali, Ngadi, Smith, & Raghavan, 2007;Evrendilek & Zhang, 2005;Jin, Zhang, Hermawan, & Dantzer, 2009;Monfort et al, 2010;Wouters, Álvarez, & Raso, 2001). The application of an external electric field causes also a sublethal injury in some of the microbial population, but it can be inactivated if recovery conditions are not suitable (García et al, 2005a;García, Somolinos, Hassani, Alvarez, & Pagán, 2009).…”

Combination of Pulsed Electric Fields with Other Preservation Techniques

“…Even so, bacterial resistance in liquid egg seemed to depend on the target microorganism, PEF parameters, process temperature and pH. The sensitivity of S. typhimurium in LWE varied according to pH (6.6-8.2) and temperature (15-40°C); its minimum level corresponded to a neutral pH and 25°C (Jin, Zhang, Hermawan and Dantzer 2009). In the case of treating egg yolk, increasing field strength, PEF treatment time and process temperature resulted in more severe cell death (Amiali et al 2007).…”

“…Moreover, counts of pseudomonads, coliforms, (2009) PEF pulsed electric field, SM skim milk, LWE liquid whole egg, HPCD high-pressure carbon dioxide, CI complete inactivation, UV ultraviolet radiation lactobacilli and staphylococci were negligible during the same period. The commercialization and safety of egg products may also benefit from the synergism of PEF and moderate temperature heating because proteins in liquid egg start to form aggregates at temperatures as low as 56°C and then their functional and physical attributes may be seriously affected (Jin, Zhang, Hermawan and Dantzer 2009). Zhao et al (2007) claimed that pulsing liquid egg white at 40°C with 800 μs at 30 kV/cm was sufficient to achieve pasteurization conditions with Salmonella enteritidis, E. coli and S. aureus as targets without altering such technical features as its foaming capacity.…”

“…Zhao et al (2007) claimed that pulsing liquid egg white at 40°C with 800 μs at 30 kV/cm was sufficient to achieve pasteurization conditions with Salmonella enteritidis, E. coli and S. aureus as targets without altering such technical features as its foaming capacity. The inactivation of 3.0-log units of S. typhimurium in liquid whole egg (LWE) was achieved by combining PEF (250 μs at 25 kV/cm) and heat (55°C); this was comparable to that obtained by pasteurization at 60°C for 3.5 min (Jin, Zhang, Hermawan and Dantzer 2009). Notwithstanding the positive results reported in LWE, Amiali et al (2007) suggested that egg yolk treated with PEF at mild temperatures must be used in conjunction with strictly refrigerated conditions since residual inoculums of E. coli and S. enteritidis could grow to levels posing a threat to public health.…”

Study of short-wave ultraviolet treatments (UV-C) as a non-thermal preservation process for liquid egg products

“…irradiation (Alvarez et al, 2007), biopreservation (Ponce et al, 1998;Boziaris et al, 1998;Calderon-Miranda et al, 1999;Lee et al, 2003), pulsed electric fields (Amiali et al, 2004;Bazhal et al, 2006;Jin et al, 2009), high hydrostatic pressure (Lee et al, 2001), hydrostatic pressure pulsing (Bari et al, 2008), and ultra high pressure homogenisation (Velazquez-Estrada et al, 2008), combination of high hydrostatic pressure with high ultra sound treatment , hydrogen peroxide treatment (Isiker et al, 2003), and pH-adjusted pasteurisation (Schuman and Sheldon, 2003), among others. All these methods are focused on the elimination of pathogens like Salmonella spp., Listeria monocytogenes, E. coli O157:H7 or Bacillus cereus.…”