Ozone based treatments for inactivation of Salmonella enterica serovar Enteritidis in shell eggs.

摘要

Illnesses due to ingestion of Salmonella enterica subspecies enterica serovar Enteritidis (Salmonella Enteritidis) increased steadily and inexplicably throughout the 1980s. Numerous risk assessment studies have demonstrated that the number one risk factor for Salmonella Enteritidis illness is the consumption of eggs or egg-containing products. As this serious health threat persisted throughout the 1990s, increased research efforts elucidated the complexity of the issue at hand. Eggs may be contaminated during or after lay, leading to the presence of cells on the egg shell, in the egg contents (in albumen or yolk), or both. While selected technologies have proven efficacious in reducing external and/or internal Salmonella Enteritidis contamination in whole eggs, products produced using these methods are far from ideal. Both extended heat treatment and application of gamma irradiation have been demonstrated to greatly reduce Salmonella Enteritidis contamination, but both processes also compromise the quality of treated eggs. A process that can combine safety with the production of a high-quality product is needed.;The objectives of this research were: (i) to evaluate the efficacy of heat and ozone combination treatment against Salmonella Enteritidis, inoculated onto the vitelline, membrane using pilot-scale equipment and to verify the acceptable quality of treated eggs; (ii) to develop a protocol sufficient to pasteurize eggs inoculated with Salmonella Enteritidis in the yolk; and (iii) to examine the chemical changes, physical quality and functionality of eggs treated with a pasteurization process. The effect of inoculation and incubation procedure on process lethality was also investigated.;Shell eggs were inoculated with Salmonella Enteritidis near the vitelline membrane (∼105 CFU/egg). Inoculated eggs were subjected to heat (57°C for 21 minutes), gaseous ozone (vacuum of 67.5 kPa broken with gaseous ozone at maximum concentration of ∼140 g m-3 and pressure of 184--198 kPa for 40 minutes) or both. Following treatment, eggs were analyzed using a modified most probable number (MPN) technique. Ozone alone, heat alone and combination treatments resulted in a reduction of Salmonella Enteritidis of 0.11, 3.1 and 4.2 log CFU/egg, respectively.;The quality of eggs subjected to this combination treatment was verified in a six week storage study. Treated and untreated eggs were held at 4 or 25°C and were subjected to weekly quality testing. At 4°C, treated and untreated eggs retained similar quality throughout storage. At 25°C, albumen quality, as defined by Haugh units and albumen pH, was maintained significantly better in treated eggs than in untreated samples.;Process parameters were fine-tuned in the design of a treatment capable of pasteurizing eggs inoculated with Salmonella in the yolk. In this study, eggs were inoculated within the yolk and incubated overnight at 30°C, allowing cells to multiply to high population (representing the worst-case-scenario for naturally contaminated eggs). Final population of Salmonella Enteritidis before treatment was approximately 10 7 CFU g-1 egg contents. Contaminated eggs were treated with heat in one of several time-temperature combinations or heat followed by ozone (vacuum of 67.5 kPa broken with gaseous ozone at maximum concentration of ∼160 g m-3 and pressure of 184--198 kPa for 60 minutes). All treatments tested resulted in greater than 6 log CFU g-1 reduction in internal Salmonella, but produced eggs varying greatly in visual appeal. From this set of treatments, one was selected for in-depth quality and functionality testing.;Physical quality and functionality of ozone plus heat pasteurized eggs was compared with that of heat pasteurized and untreated eggs over the course of eight weeks of storage, under normal storage (4°C) and temperature abuse (25°C) conditions. Quality of albumen was maintained better in pasteurized eggs than untreated eggs, regardless of storage temperature. No significant differences were observed in yolk quality. While ozone-based pasteurization reduced functionality of albumen compared to untreated eggs, heat pasteurization resulted in the greatest functionality reduction.;Several chemical analyses were performed to better assess the effect of treatments on albumen proteins. Heat plus ozone combination treatment did not damage either ovotransferrin or lysozyme, two of the predominant antimicrobial albumen proteins. Application of ozone did not significantly change the ratio of free sulfhydryl groups to disulfide bonds in albumen. Slight but not significant differences among treatments were observed with FTIR spectroscopy, indicating that the albumen of combination-pasteurized eggs more closely resembled that of untreated eggs than did albumen from heat-pasteurized eggs.;Inoculation/incubation procedures were examined throughout this research and differences in the reduction of Salmonella were observed according to several factors, including the location/depth of inoculum placement, cell density of inoculum, and incubation time and temperature. This research demonstrates that treatment with a combination of heat and gaseous ozone can be utilized to produce safe, high quality whole shell eggs.