Egg Quality Testing
Providing 14 poultry egg testing procedures in less than 4 minutes
Why measure Poultry Egg Quality parameters?
Providing high quality eggs and egg products is crucial to the sustainable economic viability of the egg industry. Surveys conducted in the EU indicated that shell strength, albumen consistency (including height) and yolk colour (intensity of yolk pigment) are the main measures of quality important to consumers. Interestingly, measures of food safety, hygiene and egg freshness ranked higher in importance than the production system used to produce the eggs. Therefore, guaranteeing quality is essential to meeting consumer expectations.
The Egg Quality System on a Texture Analyser
This system provides the tools that enable the producer and packer of poultry eggs to accurately and consistently measure the quality of their produce. They can regularly monitor a range of parameters to ensure that their eggs meet the required quality standards and that these are maintained throughout the laying period. The system is usually used on a TA.XTExpress Texture Analyser with Exponent Lite Express software which has been enabled with additional modules for this special application. The software provides the operator with parameter options from which to choose the tests to be performed on each egg.
14 measurements in 4 minutes including:
Whole Egg Weight (measured to +/- 0.1g)
Egg weight is genetically linked to all three of the major components: shell, albumen and yolk. The link between egg weight and albumen weight is higher than those between egg weight and shell or yolk weight, and as egg size increases, so does the percentage of albumen.
By placing the egg in a cradle mounted to the calibration platform of the instrument the weight of the egg can be measured and recorded in g.
Dry Shell weight (measured to +/-0.1g)
With storage, wet egg weight decreases causing a lower egg weight.
In order to measure the weight of the wet egg the dry shell weight can be subtracted from the original whole egg weight.
Shell Breaking Strength (measured to +/- 0.1g)
Shell strength, which refers to the ability of the shell to remain sound during transit from the hen to the consumer, is economically the most important of all the egg-quality characteristics. The structural quality of the shell egg is important to the processor because eggs that are structurally sound will arrive to the consumer in the best condition. Poor shell quality will result in a greater number of cracked eggs, which will result in greater losses for the producer.
The force required to crush a shell is a measure related to shell integrity and resistance to breakage. At the point of break the force is recorded in g and used as the shell breaking strength.
Shell Deformation (measured to +/-0.1mm)
At the point of breaking the compression distance is recorded. This is the degree of deformation in mm that the shell can withstand before irreversible breakage.
Egg Albumen Height (measured to +/-0.1mm)
The higher the albumen height, the better the albumen quality. The height can vary from as low as 1.5mm in stale eggs of poor quality to 12mm in good quality fresh eggs. Generally the younger the bird, producing newly laid eggs, the higher the albumen height.
Calculation of Haugh Unit and Egg Classification
The Haugh Unit has been widely accepted throughout the world as the “gold standard” for quantifying the internal quality and freshness of eggs. It is the only objective measurement of “freshness” and corresponds very closely to consumer preferences.
It is a ratio calculation involving the egg weight and thick albumen height.
The formula for calculating the Haugh unit is:
Where:
• HU = Haugh unit
• h = height of the albumen in millimeters
• w = weight of egg in grams
After the egg is weighed (in the first procedure) and the shell strength determined (optional) the egg is broken onto the egg tray. The cylinder probe is positioned in a suitable location next within the thick albumen region (immediately surrounding the yolk) and the height of the albumen is measured at the point of touching the albumen surface. The values are inserted into the above formula and a Haugh rating is calculated within the software.
The Haugh unit value ranges from 0 - 130 and can be ranked as below:
• AA : 72 or more
• A : 71 - 60
• B : 59 - 31
• C : 30 or less
The higher the number, the better the quality of the egg (fresher, higher quality eggs have thicker whites). A minimum Haugh unit measurement of 60 is desirable for whole eggs sold to the domestic consumer. Most eggs leaving the farm should average between 75 and 85 Haugh units.
Vitelline Membrane Strength/Yolk quality (measured to +/-0.1g)
With the increase in further processing of eggs, structural integrity of the vitelline (yolk) membrane has become an increasingly important issue for the egg-breaking industry. Today, millions of kilos of liquid egg products are produced each year for use in food service, commercial egg products, and as ingredients in other food products. In the egg breaking operation, liquid egg products consist of liquid whole egg, egg yolk, or egg albumen. Egg albumen is a particularly effective foaming agent that is used in baking and in the preparation of confections. Foaming ability of the egg albumen is dependent on the quality of albumen proteins, and slight crossover contamination with yolk can alter protein functionality and reduce foaming properties of the egg albumen. Recent trends in dietary improvements have also influenced many individuals to take more proactive steps to removing the yolk from the albumen when consuming egg products. Successful separation of the egg yolk from the albumen is therefore extremely important, and the strength of the vitelline membrane, particularly its ability to withstand the breaking process, is a key factor in producing good quality egg albumen.
Vitelline membrane characteristics have been seen as not only physical factors but also as microbial quality contributors in the egg. Factors influencing vitelline membrane strength are the same factors influencing albumen quality. During storage, egg quality deterioration is a factor of time, temperature, humidity, and handling. As the egg ages, egg quality deteriorates and the rate of deterioration is increased with higher storage temperatures.
The Vitelline Membrane Strength is measured by puncturing the yolk using a spherical probe. The probe approaches the yolk and measures the force (in g) to rupture the yolk.
Shell thickness (measured to +/-0.1mm)
Shell thickness is almost entirely dependent on breed, feed and the age of the bird. As the laying period progresses, egg shells become thinner. The rate of decline in shell thickness is particularly marked in the latter half of the laying year but environmental temperature and nutritional factors also influence thickness.
A 0.25” spherical probe is used to approach a small section of the egg shell (broken from the shell of the egg tested with previous procedures) and measure the thickness of the shell (in mm) at the point of contact.
Yolk Colour (using DSM Yolk Colour Fan)
When judging the quality of an egg, another criteria that consumers apply for freshness is the egg yolk colour. A simple but subjective method of determining this involves either the BASF Ovo-colour Fan or the DSM (formerly Roche) Yolk Colour Fan that expresses results in a 1 to 15 scale by means of visual comparison with calibrated cards in a fan. These fans consist of a range of paper blades coloured in fifteen possible outcomes of egg colour and numbered accordingly. The blades are held over the yolk and the colour of the yolk compared with the blades to find a corresponding blade of the same colour. This number is then assigned to the egg yolk.
The DSM Fan is a consistent, economical and readily available means of quantifying yolk colour and has become the preferred method in most parts of the world. DSM has studied consumer preferences in many parts of the world and found that, while preferences vary, consumers in most countries prefer an egg yolk color with a DSM Yolk Color Fan value of 12 or more.
Most egg marketing authorities require deep-yellow to orange-yellow yolk colours in the range 9 to 12 on the DSM Yolk Colour Fan although yolks of more intense colour may be required for specific markets. A wide variation in colour may normally be expected in the yolks from any flock. If a flock averages a yolk colour score of 10 on the DSM Yolk Colour Fan, two out of every three eggs laid by the flock will score between 9 and 11. Also, one egg in 20 will score less than 8, and one in 20 greater than 12.
Yolk Width and index calculation
The accepted quantitative measurement of yolk shape is the yolk index. It was developed by Sharp & Powell in 1930 and was defined by them as the ratio of the height to the width of the yolk (in mm) measured when the egg is broken out on a flat surface.
Yolk index is utilized to determine the shape changes in the yolk, primarily during storage. As the egg deteriorates, the yolk index decreases.
Features & Benefits of the Egg Quality System
Each test (collecting data at 400 points per second) obtains an accurate measurement. Step by step software commands and diagrams guide the operator through test procedures easily, while probes are magnetically located to enable quick removal and switching between tests.
Data from each test or batch can be printed out at the end of each testing session, and can be viewed and acted upon or archived. The software also produces a report to include means, standard deviations and coefficients of variation.
See how 14 poultry egg quality tests can be performed in less than 4 minutes: Watch our video
How does Poulty Egg Quality change?
A fresh egg is a perishable food. Immediately after the egg is laid changes in the contents start to occur and a steady decline in internal quality begins. Simultaneously, the egg starts to lose weight. The conditions of the albumen are primarily responsible for the internal quality assessment. A good quality egg is expected to have a firm and round yolk surrounded by a thick albumen and distinctly thinner outer albumen when broken out. During storage the thick albumen slowly breaks down resulting in more and more thin albumen. This albumen quality is often measured as a function of the height of the inner thick albumen. The Haugh unit is a measure of egg quality based on the height of its egg white (albumen). The test was introduced by Raymond Haugh in 1937 and remains an important industry measure of egg quality next to other measures such as shell thickness and strength. Haugh units are directly correlated to egg grading criteria. Eggs with Haugh value of 72 or higher are considered to be of AA quality.
The major factors in albumen height change are egg storage time and conditions. However, not all newly laid eggs are of the highest quality as the age of the bird, disease status and the environmental conditions of the bird are also factors that influence the initial quality of the egg and determine the starting point for subsequent deterioration. As birds age, the Haugh unit value of their eggs decreases by about 1.5 to 2 units per month of lay. Some birds consistently produce eggs with watery whites (Haugh units less than 30) later in lay, which is one reason that most commercial farms only keep their birds for one laying season. Although watery whites are thought to be mainly an indication of the increasing age of the egg, the problem can be exacerbated by high storage temperatures and low humidity.
Why is Poultry Egg Quality important?
When it comes to the separation of albumen and yolk, using automatic separators that can handle thousands of eggs per hour, the albumen quality is very important. Eggs that are too fresh present a problem when trying to separate the yolk from the albumen. Conversely, eggs that are too stale present problems of yolk breakage which then leads to contamination of the albumen. As there is a narrow range of Haugh values over which separation works well the egg processor needs to screen that day’s egg batch to identify those that would be best selected for that purpose and differentiate those out of this specification for an alternative use.
As the egg ages carbon dioxide is lost through the shell and the albumen pH increases. Water migrates from the albumen into the shell and yolk, causing it to become enlarged and flattened with a reduced cushioning effect from the albumen. With thinning of the albumen comes increased potential of the yolk to rupture when broken out which lowers consumer satisfaction of the egg quality. Higher temperatures accelerate this process highlighting the need to store the eggs at lower temperatures to decrease the deterioration and maintain eggs at their optimum quality level for a period of weeks.
Poultry Egg Quality Research
The Texture Analyser has been used widely in the poultry industry to measure egg quality parameters but here you’ll find the latest Google search of published papers.
Researchers from the USDA have published many papers regarding egg quality determination using the Texture Analyser. Read more
This system provides the tools that enable the producer and packer of eggs to accurately and consistently measure the quality of their produce.
They can regularly monitor a range of parameters to ensure that their eggs meet the required quality standards and that these are maintained throughout the laying period.
This instrument uses Exponent Lite Express software which has been enabled with additional modules for this special application. The software provides the operator with parameter options from which to choose the tests to be performed on each egg.
14 measurements in 4 minutes...
• Whole Egg Weight
• Dry Shell Weight
• Shell Breaking Strength / Shell Deformation
• Albumen Height / Haugh Unit Calculation
• Shell Thickness
• Vitelline Membrane Strength (Yolk Rupture)
• DSM Yolk Colour Fan (for manual matching / input)
Each test (collecting data at 400 points per second) obtains an accurate measurement. Step by step software commands and diagrams guide the operator through test procedures easily, while probes are magnetically located to enable quick removal and switching between tests.
Data from each test or batch can be printed out at the end of each testing session, and can be viewed and acted upon or archived. The software also produces a report to include means, standard deviations and coefficients of variation.
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