Impact of cuticle quality and eggshell thickness on egg antibacterial efficiency.

The cuticle is the first barrier against bacterial trans-shell penetration. To evaluate the cuticle quality among different colored eggshells, an efficient and reliable method is proposed in this paper on the basis of the opacity theory. It is shown that the Spearman's rank correlation coefficients between the proposed opacity method and the reported reflectance and ΔE*ab methods are all more than 0.90 in measuring the cuticle deposition for the same breed eggs, indicating that the result measured by the opacity method is credible. In addition, the validity of opacity method is also verified by the Escherichia coli penetration experiments performed on the eggs of Dwarf Layer (tinted-shelled), Hy-Line Brown (brown-shelled), and White Leghorn (white-shelled) birds. Results show that the Dwarf Layer eggs, with the thickest cuticle deposition, have the lowest bacterial penetration ratio than the eggs of the other 2 investigated breeds. We found that eggshell thickness is another important factor influencing bacterial penetration apart from the cuticle. Therefore, enhancing cuticle deposition and eggshell thickness would significantly improve the eggs' antibacterial efficiency. It is found that the antibacterial efficiency will reach as high as 98% in such a case where the cuticle opacity is over 27.5% and the eggshell is thicker than 340 μm. No significant difference was found in pore density between the penetrated and non-penetrated eggs. Moreover, according to the data for 3 regions of the penetrated eggs, we found that the sharp end shows the highest proportion of bacterial contamination compared with the blunt end and equator. The cuticle quality at equator shows a strong positive correlation between the blunt and sharp end (r2 = 0.8 and 0.7, respectively, P < 0.05). The cuticle at the equator can be selected as an indicator for cuticle breeding to improve the cuticle quality at the blunt and sharp end simultaneously. These results are of significance for the improvement of egg quality and safety in modern commercial breeding.