The effect of carbon dioxide on lysozyme activity and quality of chicken eggs

Preetha Banerjee, Purdue University

Abstract

Freshly laid chicken eggs are saturated with carbon dioxide of which approximately 40% is quickly lost within a few hours of laying. A high CO 2 content positively influences the quality and safety of eggs. Hence, it is important to maintain CO2 in eggs. Exposure of chicken eggs to a high temperature for an extended period of time increases the rate of CO2 loss. Traditional egg cooling methods require 5 to 7 days to cool eggs from 35°C at laying to the required 7°C. In comparison, rapid cooling using liquid CO2 is able to cool eggs within minutes, and it replaces any CO2 loss since laying. The goal of this research was to assess the influence of CO2 on the safety and quality of shell eggs. The first objective was to determine the effect of CO2 on the lytic activity of both purified and unpurified (egg white) lysozyme at four pH conditions (4.5, 6.5, 8.0 and 9.5) and two temperatures (5°C and 22°C). The second objective was rapid cooling shell eggs using liquid CO2 and evaluating its effect on quality over 12 weeks of refrigerated storage. The two objectives were carried out as separate experiments. For experiment one, the activity of lysozyme was assessed on bacterial cells, Micrococcus lysodeikticus. Results showed that lysozyme was always more active at 22°C as compared to 5°C. Also, purified egg white lysozyme activity was greater than that of egg white with equal lysozyme content. The highest lytic activity was found at pH 6.5 and 22°C. CO2 treatment increased lytic activity under all cases except at pH 9.5. At pH 4.5, the addition of CO2 increased lytic activity of purified lysozyme by more than 50% at both temperatures. At pH 6.5 a slight reduction in lysozyme activity was observed with carbonation; however, it was not significant at 5°C. At pH 8.0, lytic activity increased by over 100% at 5°C and 23-100% at 22°C. At pH 9.5, lytic activity without CO2 addition was high; however, carbonation completely eliminated lytic activity. Thus, CO2 treatment may influence lysozyme activity. In the second experiment, cooling conditions were optimized to achieve a 7°C egg center temperature after cooling and equilibration. Three cooling conditions which met this condition were selected for further comparison in CO2 uptake evaluation: 18 min at -45°C (treatment A); 15 min at -60°C (treatment B) and 12 min at -75°C (treatment C). For quality evaluations all treatments were compared to the control, which was traditionally cooled to 7°C. Results showed that rapid cooling significantly increased Haugh Unit value of eggs (HU 76-78) compared to control (HU 71.8). Rapidly cooled eggs had 116% more AA grades eggs compared to traditionally cooled eggs over the 12 weeks of refrigerated storage. Yolk and albumen pH were not found to be significantly different between the control and the treatments, except treatment C for which the yolk pH was significantly lower than the rest through out the 12 week study. Rapidly cooled eggs (approximately 1.8 mg/g albumen) maintained a significantly higher CO2 content than traditionally cooled eggs (1.3 mg/g albumen) over the 12 weeks of storage. Rapid cooling with liquid CO2 significantly increased the vitelline membrane strength (VMS). The VMS of the traditionally cooled eggs decreased by 50% over the 12 weeks of storage whereas the rapidly cooled eggs showed a high VMS throughout. Overall, results indicated that rapid cooling using liquid CO2 maintained egg quality and extended the shelf life of eggs up to 12 weeks.

Degree

M.S.

Advisors

Keener, Purdue University.

Subject Area

Food Science

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