Effects of cool water washing of shell eggs on haugh unit, vitelline membrane strength, aerobic bacteria, yeast, and mold
Type of DegreeThesis
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Most retail shell eggs in the United States are washed in water that can be upwards of 49°C which increases the internal temperature of shell eggs. After processing, internal egg temperatures may be 6.1 to 7.8°C higher than initial internal egg temperatures. The internal post-processing temperature of shell eggs fall within the growth range of Salmonella Enteritidis (SE), the most common human pathogen associated with eggs and egg products. It can take several days for the internal temperature of processed packaged eggs to reach a temperature that is cool enough to inhibit the growth of most microorganisms, including SE. Washing eggs with cool water may be a way to prevent the increase in internal egg temperature during processing. Experiments were conducted to study the effects of cool water washing on shell egg quality. The presence of aerobic bacteria, yeasts, and molds on exterior shell surfaces, in the contents, and within the shell matrix of eggs were also examined. Egg quality was evaluated by Haugh unit and vitelline membrane strength determination. This study was conducted in two phases. Phase one consisted of a pilot study, in which six different dual tank wash water temperature combinations, including a single warm water temperature (49°C) and two cool water temperatures (15.5°C and 24°C), were used to wash eggs. The pilot study was conducted in order to identify the best temperature, or combination of temperatures, for washing shell eggs while limiting the increase in the internal egg temperature. Phase two consisted of a commercial study in which shell eggs were washed using four different dual tank wash water temperature combinations in two commercial egg processing facilities. The commercial study examined how commercially washing shell eggs in cool water affects interior egg quality, as well as the presence of aerobic bacteria, yeasts, and molds on and within the egg. The pilot study and the commercial study each included ten weeks of storage in which the presence of aerobic bacteria, yeasts, and molds on exterior shell surfaces, in the contents, and within the shell matrix of processed eggs were monitored weekly. Microbial quality was monitored by the USDA Agriculture Research Service Egg Safety and Quality Research Unit. Egg quality was also monitored during both the commercial and pilot study. During the pilot storage study, no significant differences in Haugh unit values or vitelline membrane strength were found between wash water temperature combinations, indicating that cool water washing does not affect the egg quality measurements monitored. However, results from the pilot study showed significant differences (P = 0.05) in vitelline membrane strength and the Haugh unit values as storage time progressed. The average force required to break the vitelline membrane decreased 13.9% and average Haugh unit values decreased from 59.2 to 56.4 due to storage. The results of the commercial study indicate that wash water temperature did not significantly affect Haugh unit values or vitelline membrane strength. As storage time progressed, however, average Haugh unit values declined 14.8% and the average force required to rupture the vitelline membrane decreased 20.6%. Although no significant differences were found among wash water temperature schemes in amounts of aerobic bacteria, yeast, and mold present on exterior shell surfaces, within the shell matrix, and in egg contents, average amounts of bacteria present on shell surfaces also decreased 11.3% during storage, and bacteria present in egg contents increased 39.5% due to storage. Results of the commercial study indicate that there is a potential for utilizing cool water washing in the commercial setting while still producing safe eggs.