Maximizing carbon dioxide content of shell eggs by rapid cooling treatment and its effect on shell egg quality

Rapid cooling of shell eggs using liquid CO₂ has been shown to cool eggs to 7°C within minutes, as opposed to days required by traditional cooling treatments. This quick-cooling technique is component in the maintenance of egg quality and extended shelf life beyond the current 30- to 45-d period. The hypothesis for the current study was that maximizing CO₂ content of the eggs during cooling may increase Haugh units and thus extend shelf life (physical quality factors). The objective of this study was to maximize CO₂ content of shell eggs during rapid cooling with liquid CO₂ and determine its effect on egg quality during 12 wk of refrigerated storage. Three cooling conditions selected for the study were -45°C for 18 min (treatment A), -60°C for 15 min (treatment B), and -75°C for 12 min (treatment C). After rapid-cooling treatment, it took approximately 25 min for the internal temperature of eggs to equilibrate to 7°C. The Haugh units of the rapidly cooled eggs were significantly higher than the traditionally cooled (control) eggs. After 12 wk of refrigerated (5-7°C) storage, control eggs were only 37% AA-grade, 57% A-grade, and 6% B-grade. In comparison, all the rapidly cooled eggs averaged to 80% AA-grade and 20% A-grade. After 6 wk, the average quality of control eggs reduced to grade A, whereas rapid cooling treatment was able to maintain AA quality up to 12 wk. The CO₂ content of the rapidly cooled eggs (1.8 mg of CO₂/g of albumen) showed no difference between treatments A, B, and C, but it was significantly higher than the control (1.3 mg of CO₂/g of albumen). In addition, the vitelline membrane strength of the control decreased 65% during storage and was between 30 and 50% of the vitelline membrane strength of CO₂-cooled eggs at 12 wk. Rapid cooling with liquid CO₂ extends shelf life of shell eggs.