Physicochemical Index Analyses of the Egg White in Blue-Shelled Eggs and Commercial Brown-Shelled Eggs during Storage

Abstract

To compare the physical and chemical changes in egg whites during storage, assisting in the evaluation of differences in egg freshness between various chicken breeds, we chose 240 blue-shelled eggs (Blue group) and 240 commercial brown-shelled eggs (Brown group) that 28-week-old hens had laid. In this study, all eggs were stored at 25 °C. The egg weight, egg components' weight and proportion, Haugh Unit value and the contents of S-ovalbumin, ovomucin and lysozyme in the thick albumen (KA) and thin albumen (NA) were measured at eight time points every 3 days until the 21st day of storage. The eggshell, yolk and KA proportions in the Brown group were significantly lower, whereas the NA proportion was significantly higher than that in the Blue group (p < 0.001). The Haugh Unit value and S-ovalbumin in the Brown group were significantly higher, whereas KA ovomucin and NA lysozyme were significantly lower than those in the Blue group (p < 0.001). There existed significant negative correlations between the KA and NA, irrespective of weight or proportion. The Haugh Unit value was significantly positively correlated with lysozyme and ovomucin, but significantly negatively correlated with S-ovalbumin. During storage, the KA weight (proportion), Haugh Unit value, lysozyme and ovomucin decreased, whereas the NA weight (proportion) and S-ovalbumin increased. At each time point, the NA lysozyme in the Brown group was lower than that in the Blue group (p < 0.05). After storage for 6 days, the KA ovomucin in the Brown group began to be lower than that in the Blue group (p < 0.05). The study showed that the weight (proportion) differences in egg components between blue-shelled eggs and commercial brown-shelled eggs are mainly due to the NA. The Haugh Unit value and albumin protein indexes of blue-shelled eggs were better than those of brown-shelled eggs, and showed mild changes during storage, indicating the better storage performance of blue-shelled eggs.

Keywords: S-ovalbumin; albumin protein; blue eggshell chicken; brown eggshell layer; egg; lysozyme; ovomucin.

Figure 1

Changes in the proportion of the main components of egg during storage. Subfigure (A) shows the changes in eggshell proportion and yolk proportion, whereas subfigure (B) shows the changes in the thick albumen proportion and the thin albumen proportion. Brown: the Brown group of eggs from commercial brown eggshell layer; Blue: the Blue group of eggs from blue eggshell chicken; ESP: eggshell proportion; EYP: egg yolk proportion; KAP: thick albumen proportion; NAP: thin albumen proportion.

Figure 2

Changes in Haugh Unit and albumin protein components during storage. Subfigure (A) shows the changes in Haugh Unit, whereas subfigures (B–D) show the changes in S-ovalbumin, lysozyme and ovomucin in thick albumen and thin albumen, respectively. Brown: the Brown group of eggs from commercial brown eggshell layer; Blue: the Blue group of eggs from blue eggshell chicken; KA: thick albumen; NA: thin albumen.