Application Brief: LI200 Ecutimeter
The LI200 Ecutimeter measures the outer cuticle of poultry eggs, but what is the outer cuticle and why is it important? This Application Brief gives an overview of the cuticle and its importance in ensuring good quality eggs, improving both the profitability of the supplier and reducing risks faced by consumers.
What is the cuticle?
The cuticle is the outermost layer of the poultry egg. It is a very thin protein layer, typically around 10 μm thick, on the outside of the shell and is the first line of defence against infection by bacteria including E-coli and Salmonella. As such, maintaining the quality of the cuticle through the breeding, laying, packaging and supply cycles is a vital aspect of ensuring the safety of the poultry egg and food supply chain. For this reason, there is an ongoing research effort to help with genetic selection for breeders to produce hens that lay with better cuticles. In spite of its importance, there are few routine methods of determining the condition of the cuticle.
The importance of the egg cuticle
The role of the cuticle has been studied for over forty years to determine its importance in defending eggs from bacterial infection1. The poultry industry relies on artificial incubation of eggs to prevent the transfer of potentially harmful bacteria from one generation to the next. Despite this, the vertical transmission, i.e. transmission through reproduction, from both meat and table egg laying birds to production flocks has been identified as the most likely route of transfer of antibiotic resistant E-coli and Salmonella2. There is also opportunity for horizontal transmission, i.e. non-reproductive environmental transmission, to occur during the collection and transportation of eggs.
The cuticle layer, although thin, has been shown to significantly reduce the penetrability of the shell to infection by bacteria such as Salmonella tryphimurium1–3 and has led to a drive for the understanding of the construction of this layer4.
A schematic of an egg, its shell and associated layers is shown below along with a transmission electron microscope (TEM) image of the egg surface showing cracks in the cuticle layer5.
A schematic of the makeup of a chicken egg showing the various membranes of the shell (top), a TEM image of the
surface of an egg (bottom)
The cuticle can be seen to be a very thin incomplete layer on the egg surface. The following figure, produced by Bain et al2, shows the correlation between cuticle deposition and resistance to infection by E-coli demonstrating its ability to block infection.
Furthermore, studies have shown the effect of both hen age and egg freshness on the integrity and quality of the egg cuticle layer coverage. Rodrígues-Navarro et al6 show that significant changes occur in the first 24hrs after laying, an effect of the drying of the egg surface, and so particular care should be taken during this time. In addition, younger hens, in their first year, produce more lipid rich consistent cuticles than older birds with the bulk of the decrease in cuticle component production towards the end of the laying cycle.
Whilst the studies discussed above use a variety of methods to assess the cuticle, such as TEM and attenuated total-reflection-Fourier transform infra-red spectroscopy (ATR-FTIR), these are research grade methods requiring expensive, difficult-to-use instruments. For routine/quality assurance measurements, cheaper, easier-to-use approaches are necessary. One such method entails the use of reflectance spectroscopy of eggs stained with a protein dye designed to attach to the cuticle. Such a method has been used for a long time as a qualitative measure but was recently developed into a quantitative approach by Bain et al.
This forms the design principle for the LI200 Ecutimeter.
The cuticle is a key element of poultry eggs, acting to prevent bacterial infection. Understanding and eliminating such infection is an important determinant of egg quality and hence producers’ profitability and consumer safety.
Till now, only research-grade approaches were available to determine the quality of the cuticle. Using standard methods, Lomond Instruments has produced an instrument which allows rapid, cost-effective analysis of egg cuticle. This will have important benefits to producers and suppliers in terms of both profitability and product quality.
1. Williams, J. E., Dillard, L. H., and Hall, G. O. The Penetration Patterns of Salmonella typhimurium through the Outer Structures of Chicken Eggs. Avian Dis. 12, 445–466 (1968).
2. Bain, M. M. et al. Enhancing the egg’s natural defence against bacterial penetration by increasing cuticle deposition. Anim. Genet. 44, 661–668 (2013).
3. Munoz, A., Dominguez-Gasca, N., Jimenez-Lopez, C. & Rodriguez-Navarro, A. B. Importance of eggshell cuticle composition and maturity for avoiding trans-shell Salmonella contamination in chicken eggs. Food Control 55, 31–38 (2015).
4. Rose-Martel, M., Du, J. & Hincke, M. T. Proteomic analysis provides new insight into the chicken eggshell cuticle. J. Proteomics 75, 2697–2706 (2012).
5. Solomon, S. E. 1997. Egg and eggshell quality. Manson Publishing Ltd., London, UK.
6. Rodriguez-Navarro, A. B., Dominguez-Gasca, N., Munoz, A. & Ortega-Huertas, M. Change in the chicken eggshell cuticle with hen age and egg freshness. Poult Sci 92, 3026–3035 (2013).