Measurement of Egg Quality
- To assess egg quality of both fresh and stored eggs, using Haugh unit, yolk index and pH.
- To demonstrate the buffering capacity of egg albumen in both fresh and stored eggs.
- To use the data determined in 1 and 2 to examine changes in egg quality on storage.
Introduction to Practical
The contents of an egg are approximately 64 parts white (albumen) and 36 parts yolk by weight. The albumen is composed of four fractions: outer thin albumen, inner thin albumen, thick albumen and the chalazae. The yolk is enclosed by a vitelline membrane and suspended in the centre of the egg by the chalazae which are attached to the surface of the egg membrane.
The eggshell contains thousands of tiny pores and, after an egg is laid, these permit exchange of gases with the atmosphere. On laying, albumen pH is about 7.6 but loss of carbon dioxide to the atmosphere leads to an increase in albumen pH to about 9.3 and this results in changes to some of the albumen proteins, resulting in a thinning of the egg ‘white’.
These changes affect egg quality and can be monitored by measuring:
- Haugh Unit of the thick albumen and
- Yolk Index, a measure of vitelline membrane properties and yolk quality.
The pH change within the egg white is buffered by bicarbonate, the efficacy of which changes during storage as CO2 is lost.