24 Internal Quality of Egg

Kulsum Jan

Quality

Quality : Degree of excellence
Those conditions and characteristics that consumers want, and are willing to pay for, are, in a broad sense, factors of quality
Egg is determined by comparing a number of factors
Quality factors for eggs may be divided into two general groups

Introduction

However, internal egg quality is relatively unstable and deteriorates from the time it is laid until it is consumed

The Air Space

Laid Egg : Warmer than its surroundings
On cooling : Contracts and a small air space is formed between the inner and the outer shell membrane
The air space generally forms at the broad end of the egg as there are more pores in this part of the shell
With age : moisture and carbon dioxide continue to be lost through the pores
Air moves in and the air space increases in size
The warmer and drier the air, the quicker the moisture loss from the egg.
Size of air cell : As an approximate guide to the quality and age of an egg
Judged objectively : Air-cell gauge
In candling : Considered a relatively unimportant quality factor for determining internal quality when compared to the broken-out appearance of an egg
Depth is the only quality factor considered with the air cell.

Descriptive terms for air cell

Depth of air cell : distance from its top to its bottom when the egg is held air cell upward
Free air cell : An air cell that moves freely towards the uppermost part in the egg as the egg is rotated slowly
Bubbly air cell small, separate main air cell: A ruptured air cell resulting in one or more air bubbles, usually floating beneath the

Albumen Quality

In fresh, good quality : Albumen is jelly-like and may have a cloudy appearance
With age : Albumen becomes transparent and increasingly watery
At higher temp : the rate of carbon dioxide loss is higher and the visible signs of ageing occur quicker
Quality : Measured by the height in millimetres of the outer thick albumen
During storage : It is the proteins in the thick albumen which begin to break down due to alkalinity
At the same time, water slowly migrates into the yolk thus the yolk becomes enlarged and flattened on breakout.
The yolk moves away from the centre of the egg and may eventually rest against the shell itself
Breakdown of the albumen makes the egg extremely vulnerable to microbial invasion

Yolk

The appearance of the yolk as the egg is twirled in candling is one of the best indicators of the interior quality of shell eggs
Characteristics : Determined by shadow that it casts upon the shell before the candling light
Appearance : Dependent on the condition of the white prior to packing
With age : The rate of carbon dioxide and moisture loss in the white increases and affects the condition of the white
Three factors : Distinctness of yolk shadow outline, size and shape of yolk, defects and germ development.

Quality Parameters of Yolk

The thickness and consistency of the white. The thicker the white, the less distinct the outline appears, as yolk is prevented from moving close to the shell.
Condition of the yolk : Determined by the presence or absence of blemishes that show up before the candling light as dark shadows on the yolk, or the presence or absence of an off-colored yolk appearance which shows as a greyish or greenish shadow
Colour of the yolk : Difficult to determine the colour of the yolk before the candling light except off-coloUr. Sometimes yolk colour influences the candler’s judgment. An extremely deep-colored yolk, under some conditions, would cast a darker shadow than would a lighter yolk.

Size and shape of yolk.

Freshly-laid egg : Round and firm
Aged Egg : Yolk membrane weakens allowing water to be absorbed from the white
Increase in size results in stretch and weaken the vitelline membrane and to assume a somewhat flattened shape on top and an “out of- round” shape generally, resembling a balloon partially filled with water
Yolk size and shape are mentioned only in the lowest quality classification for eggs – B quality – where these factors become apparent

Standards of yolk quality

Outline slightly defined — A yolk outline that is indistinctly indicated and appears to blend into the surrounding white as the egg is twirled (AA quality).
Outline fairly well defined — A yolk outline that is discernible but not clearly outlined as the egg is twirled (A quality).
Outline plainly visible — A yolk outline that is clearly visible as a dark shadow when the egg is twirled (B quality).

External quality

Egg shell : quality is given throw the weight and the percentage of shell, thickness and the strength
The differences in egg shell quality depend on the environmental conditions and the feed quality and also of strain of layers
Egg weight : Affects egg shell thickness and egg size as well
Brown egg layers produce higher shell weight in comparison with some other hybrids of white colour, but the egg shell deformation in brown eggs is usually higher
However, negative correlation on egg shell deformation and the strength as well as thickness is found in brown eggs.

Conclusion

Egg shell quality and egg internal quality are of major importance to the egg industry worldwide
Eggs for processing should be visibly clean prior to breaking and separating. Cracked eggs may be processed
Broken eggs should not be processed and should be disposed of in a safe manner
Eggs deteriorate rapidly during storage under ambient conditions
Dirty eggs should be disposed of in a safe manner or may be cleaned, separating of egg contents from the shell should be done in a manner
Avoid contamination by personnel or from equipment, and that permits examination of egg contents.

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Suggested readings

Baek S.B. (1990). Study on the estimation of genetic parameters for the compositions and egg qualities in Korean native ogol fowl. M.Sc. Thesis, Chung Nam National University.
Dudusola. I. O. Comparative evaluation of internal and external qualities of eggs from quail and guinea fowl. International Research Journal of Plant Science (ISSN: 2141-5447) Vol. 1(5) pp. 112-115, November, 2010
Lieu, Eng-Hwa, G. W. Froning, and R. Dam, 1978. Effect of storage on lipid composition and functional properties of dried egg products. Poultry Sci. 57:912–923.
Song KT, Choi SH, Oh HR (2000). A Comparison of Egg quality of Pheasant, Chukar, Quail and Guinea fowl. Asian – Aus. J. Anim. Sci. 13 (7): 986 – 990).
Stadelman WJ (1977). Quality preservation of shell eggs. In Egg Science and Technology (2nd edition) (Ed. W. J. Stadelman and O. J. Cotterill). AVI publ. Co., Inc., Westport, C. T. pp 41– 47.
USDA (1983). Egg grading manual; USDA, AMS, Agriculture handbook 75. U. S. Government Printing Office, Washington, DC.
U.S. Department of Agriculture, “USDA Laboratory Methods for Egg Products,” (C&MS PY Notice, No. 150), U.S. Department of Agriculture, Washington, D.C., March 1 S, 196.