Introduction to egg quality assessment
This is particularly true of the eggshell. The complex dimensions and structure of the shell creates unique problems for biologists and engineers in their endeavour to unravel its complexities. Unfortunately, much of this research has raised more questions than answers.
Despite this research, shell faults still create the greatest financial loss at commercial level and there is little indication of improvement.
Several items need to be mentioned about methods to maintain higher interior egg quality and prevent the breakdown of egg albumen and yolk. It has been shown that an egg will lose on the average of about 2 percent of its weight when held at 10 deg C compared with 5 percent of its weight when kept at 20 deg C after 20 days of storage. Hence, the main method utilised to maintain high interior egg quality is to store eggs at a relatively cool temperature of 7-8 deg C or lower.
It is also important to maintain a relatively high humidity (70-80 percent) in the egg storage area. Since eggs lose moisture due to increased storage time and temperature, the high humidity environment will slow this process down. Use of low storage temperatures will help maintain the good functional properties of both albumen and yolk, reduce loss of carbon dioxide through the shell from the albumen, and help maintain albumen pH.
As soon as the egg is laid, its quality begins to decline. As storage time increases, the overall egg quality as measured by conventional grading standards declines.
The albumen has a major influence on overall egg quality. In the intact egg, it controls the position of the yolk, which in turn has a significant physical influence on the microbiological defense of the egg.
Within the intact egg, the albumen consists of concentric layers of colourless gel and liquid. When a fresh egg is carefully broken out onto a smooth, flat surface, the round yolk stands proud in a central position surrounded by a pouch of thick albumen containing liquid and an outer thin layer.
Early attempts to assess albumen quality in broken-out eggs used the area of spread of the albumen as an indicator, and the USDA produced standard charts in order to formally categorise the degree of staleness into grades.
A more qualitative approach was introduced by Haugh (1937), and despite some critical appraisals, Haugh units have remained the standard evaluation of albumen quality.
In any consumer survey of egg quality, yolk colour ranks high and preferences vary between countries. Subjective techniques rely on colour comparisons with standard coloured solutions, discs, rings and fan blades.
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Article made possible through the contribution of EPAC.