Decontamination Because egg decontamination effectively reduces the bacteria load on an eggs surface and prevents rapid penetration, it should be carried out as soon as eggs are collected. Ways to decontaminate eggs include different detergents in wash water, such as free chlorine, new N-halamine compounds, and an iodine-based disinfectant, (Worley and others 1992; Knape and others 2001), electrolyzed oxidative water (Russell 2003), microwave (Mudau 2007; Sivaramakrishnan 2007), ultrasonic in combination with heat and/or pressure treatment (Piyasena and others 2003; Cabeza and others 2004, 2005), ozone, and UV (ultraviolet radiation) (Rodríguez Romo 2004). The use of egg washing is a continuous debate despite its broad commercial application. Current concerns focus on whether egg washing increases the internal microbial load. Within the European Union, egg washing is prohibited except in Sweden and parts of the Netherlands. The reason offered is that egg-washing procedures may damage the quality of the cuticle enhancing the opportunity for bacterial invasion (Peebles and Brake 1986; Bialka and others 2004; EFSA 2005). Factors related to cuticle damage caused by egg washing include presence of water on the eggshell, presence of iron in the wash water, physical brushing damage, and high pressure (Commission of European Communities, 2003). These are the reasons that class A eggs for human consumption are not eligible for the practice of egg washing by European Union legislation and eggs will be downgraded if any forms of disinfection are used. However, this reasoning is at odds with research that showed the washing procedure did not appear to affect the incidence of open pores and the overall cuticle quality. Meanwhile, it was also indicated that brown eggs in general were of better quality in terms of their cuticle scores than the white eggs when 4 standards, such as mechanical damage, debris, open pores, and cuticle coverage, were considered (Messens 2009). And the use of egg washing is yet authorized in Canada, America, Japan, Australia, Russia, and Mexico for the reason that egg washing can reduce the total microbial load on the surface of sanitized eggs by approximately 2 to above 5 log units (Hutchison and others 2004; Rodríguez Romo 2004).
Given the controversy on the advantages and disadvantages of egg washing, other procedures are being evaluated. Hierro and others (2009) used pulsed light (PL) as a method of egg decontamination and the effects were more notable when the cuticle was preserved intact. In addition, this treatment is most effective when applied as soon as eggs are laid. And, it is limited by the motility of Salmonella and low penetration depth of UV radiation. Hot air treatment for table eggs (2 shots for 8 s at 600 °C with an interval of 30 s of cold air) reduced Salmonella load up to 1.9 log units without significant changes for any of the egg's quality traits, such as the cuticle, breaking strength, and yolk index (Pasquali 2009). Nonthermal atmospheric gas plasma device, a resistive barrier discharge prototype able to generate an ionized gas containing free electrons and neutral reactive species such as atoms, molecules, and radicals at atmospheric conditions, which is able to reduce Salmonella load up to 4.5 log units per eggshell with a humidity of 65% at 25 °C for 90 min of treatment, provides a decontamination choice for farmers and industries that need stock eggs for a relatively long period (Ragni and others 2010). However, the time and cost needed for this method may become a limitation for its practical use in commercial production.
In hot water immersion, heat is transferred from hot water through the eggshell all the way to the inside egg contents until the center of the yolk reaches the desired temperature for sufficient time. In light of early research findings, the use of hot water immersion at 57 °C for 25 min followed by hot air heating at 55 °C for 60 min resulted in a 7 log unit reduction of Salmonella in shell eggs and produced acceptable changes on egg qualities at the same time (Hou and others 1996). The patent of Davidson and others (2004) indicated that the heated fluid bath with a temperature of between about 128 to 145 °F allows a reduction of at least 4.6 log units of any Salmonella bacteria within the eggs. This followed by antibacterial gas treatment and further wax cover could result in at least another 5 log units reduction of bacteria and provide additional antibacterial barriers to egg contents. And, this method is commercially used by Davidson's pasteurized eggs. Nevertheless, pasteurization methods employing liquid immersion or spray washing of shell eggs are prohibited under certain regulatory schemes in many European countries due to possible undesirable effects to egg quality (Ball and others 2002). Schuman and others (1997) revealed that 50 to 57.5 min treatment with a bath temperature of 58 °C or 65 to 75 min treatment with a temperature of 57 °C increased Haugh unit values and had no influence on albumen pH values and yolk index but that it affected albumen clarity and functionality.
In addition to Salmonella disinfection, an effective measure for preventing Salmonella growth in egg contents is necessary. The rapid cooling was introduced to cool eggs from 40 or 45 °C to 7 °C in approximately 15 min or less, which may take 7 or 10 d in conventional conditions, to suppress the significant bacteria multiplication (Keener and others 2000b). Moreover, rapid cooling was also found to improve internal egg quality and increase shelf life (Sabliov and others 2002). Further study showed that rapid cooling with CO2 produces higher quality eggs with increased shelf life than rapid air cooling but with no difference on Haugh units unless followed by subsequent storage in CO2 (Keener and others 2000a). Although rapid cooling might cause slight cracks in eggshells, if well managed, it is a good way for controlling Salmonella growth on the whole (Thompson and Knutson 2000).
Most importantly, though lots of work can be done for shell eggs, secondary pollution in the process of packing and palletizing may also introduce Salmonella to decontaminated eggs. Thus, decontamination should not only focus on the egg itself, but the equipment for egg storage as well.
Storage Storage conditions present issues in contamination with focus on duration, temperature, and environmental hygiene. Different countries have different regulations. Storage limits for table eggs in the United Kingdom were 3 wk at 8 °C (Kinderlerer 1994), while in Israel 3 mo for refrigerated eggs and 16 d at room temperature (Lublin and Sela 2008). In many countries, eggs are required to be stored at low temperatures to restrict microbial growth. In Germany, legislation required that egg cooling be applied at 5 to 8 °C for 18 d maximum post lay (EFSA 2009). And in the United States, either shell eggs packed for consumers or eggs that receive a treatment from egg producers were required to be kept at 45 °F (7.2 °C) no later than 36 h after the eggs are laid during storage and transportation (FDA 2010). In this scenario, it is more advisable to apply low-temperature storage in order to minimize the possibility that eggs infected with S. Enteritidis are transmitted to humans. This recommendation is supported by the study of Gast and Holt (2000), which showed that low temperatures were more effective for controlling S. Enteritidis multiplication in the yolk when high concentration of S. Enteritidis was artificially introduced into egg contents. (Gast and Holt 2000). On the other hand, low temperature can slow down the process of penetration (Chousalkar and others2010). However, Kang and others (2006) suggested that it is preferable to store eggs at 37 °C for a certain period of time first, instead of 4 °C directly, to allow the endogenous bactericidal activity of egg albumen to kill the contaminating S. Enteritidis. This reasoning is valid especially when most eggs are infected through trans-shell contamination. While in the case of vertical transmission, this application awaits more research. Further studies show that, although low preservation temperature for table eggs will limit the multiplication of Salmonella, it does not reduce the existing Salmonella concentration. It may indeed prolong the survival of Salmonella because Salmonella may be increased by low storage temperature (Baker and Balch 1962; Radkowski 2002; Messens and others 2006) and reduced with higher temperature (Rizk and others 1996).
From the aspect of an egg's structure, Humphrey and Whitehead (1993) showed that storage had little direct impact on albumen with respect to the growth of Salmonella, but rather, it influenced the integrity of the vitelline membrane that might result in a difference in Salmonella multiplication in the albumen and yolk. The pH of the albumen rose along with the storage time, and finally led to the dissipation of fibers contained on the vitelline membrane of fresh eggs, as well as the decline in protein and hexosamine content of the vitelline membrane (Fromm 1967). Consequently, it is easier for the bacteria to either invade the yolk or obtain nutrients from it. Therefore, cooling practices should to be carried out shortly after lay to keep eggs fresh and also to prevent Salmonella multiplication in eggs. Besides, the speed with which changes in membrane integrity occur as during storage, it is also highly temperature dependent. No significant changes occurred over 3 wk of storage at 20 °C, whereas apparent changes occurred only after 7 to 10 d of storage with temperatures fluctuating between 18 and 30 °C (Humphrey and Whitehead 1993). Thus, it is highly recommended that eggs should be kept in a cooling environment and temperature fluctuation be avoided during egg storage.
Additional concern for egg processing Eggshell is especially fragile so special care should be taken in the process of egg handling. The data by USDA showed that 177 million dozen shell eggs were cracked during August 2010, 3% up from a year ago (USDA 2010). A cracked egg loses part of its defense system, thereby is in danger of Salmonella invasion. Cross-contamination, on the other hand, always happens in transportation and egg processing. Therefore, safety education for egg handlers is necessary to mitigate Salmonella dissemination and egg products should be pasteurized. It was estimated that the annual number of illness would be reduced from 5500 to 3200, if all liquid egg products produced in the United States were pasteurized for a 6 log units reduction of Salmonella (FSIS 2005). Outreach efforts should stress the importance of properly cooking eggs. Salmonella are susceptible to heat treatment. Temperatures above 55 °C for enough time are sufficient to destroy Salmonella. Uncooked and semi-cooked eggs should be avoided for the public.