Quality Of Eggs
quality Of Eggs defined as the inherent characteristics of an egg which determines its degree of superiority and which is liked by customers. The producers fetch a better price for the good quality products and customers always prefer the product of assured quality.
Some significant egg qualities are egg size, egg shape, shell color, shell condition, Eggshell thickness and strength, albumen quality, yolk quality, air cell quality, etc. For evaluation of these quality parameters, the requirements are as follows:
i) Egg weighing balance (for egg size)
(ii) Vernier Caliper (for egg shape)
(iii) Egg candler which is wax or electric(for shell soundness; air cell, albumen and yolk qualities)
(iv) Screw gauge (for shell strength)
(v) Scale expressed in cm and mm (for the depth of air cell)
(vi) Glass containers (for egg contents, etc.)
(vii) Special types of Brine solutions of known specific gravity ranging from 1.062 to 1.09.0 (for specific gravity of egg
The procedure of determinating the quality of eggs is essential and which are easily evaluated by the two distinct criteria. Now we discuss the system to determine the quality of eggs.
a) External qualities of eggs
It is further identified by the following points such as Egg size, egg weight, egg shape, shell soundness, shell color, eff shell condition, eggshell strength, etc
(1) Egg size/Egg weight
The terms called ‘egg size’ and ‘egg weight’ are used synonymously. The egg size is
weighted simply with the help of egg weighing balance.
The standard weights of table eggs of different species are –
Turkey Egg 85 gram
Duck Egg 70 gram
Quail egg 10 gram
Chicken Egg 58 gram
The normal shape of an egg is oval. Slight abnormality in the shape of an egg (like elongated, flat, round, conical, etc.) is not preferred by consumers, because they though abnormal eggs are laid by diseased birds. Besides these, the bad shaped eggs are not suitable for hatching purposes.
The egg shape is measured by Vernier Caliper in terms of egg shape index (ESI). The length and breadth of an egg are to be measured to nearest O.lmm and the breadth-length ratio is to be multiplied by 100 to get the ESI. BESI = LX 100The higher egg shape index indicates round shape and the lower index indicates an elongated egg.
The optimum shape indices of eggs of various poultry species are
The shell color of the egg is very characteristic of the breeds of poultry. The breeds of Mediterranean class (e.g. White Leghorn, Minorca, Ancona) always lay white shelled eggs. The breeds of American class (e.g. New Hampshire) and English class (e.g. Australorp, Sussex) always lay a brown shelled egg.
Quail eggs are tinted with different colors. (Nowadays quail strain is produced which lays white shelled eggs.) The shell of a duck egg is more transparent than a chicken egg.
The dull or stained color of the eggshell is not preferred by the consumers. Note: The shell color of the egg has nothing to do with its quality. So it is not included in the USDA egg standards.
Shell cleanliness: It is judged by visual observation. On the basis of the degree of cleanliness, the eggs are classified into four groups, viz., clean, slightly stained, moderately stained and dirty.
Clean egg: The shell is totally free from foreign material including stains.
A bit of stained egg: The shell is free from dirt but having a few stains covering up to 1/161h of its surface area.
Moderately stained egg: The shell is free from dirt but having a moderate degree of stains covering up to one-fourth of its surface area.
Filthy egg: The shell has both dirt and stains covering more than one-fourth of its surface is.
A standard grade chicken egg (around 58 g) has a surface area of about 68.00sq.cm. and its 1/4th and 1/16th parts mean an approximate area of 4.12cm x 4.12cm and 2.05cm x cm, respectively.
Shell soundness: A sound egg means an egg with an intact and unbroken shell. An unsound egg may be cracked (having a hairline crack on the shell), leaking ( a huge breach on shell and shell membranes leading to oozing of egg contents) and smashed (having crushed shell).
Cracked Egg: The cracked egg is of poor quality and leaking and smashed eggs are supposed in the category of loss (according to USDA grading of eggs).
The discharge and smashed eggs: It may be identified by visual observation. For identification of hairline crack on the shell, candling is to be done. the Candling of eggs means viewing through egg by holding it in front of a source of light (or candler) in a dark room.
Egg candler is a wooden or metal box closed from all sides except an egg-sized aperture (2.5cm diameter) on one side and Has an electric bulb fitted inside the box. Observation is to be taken while viewing constantly and twirling the egg before the aperture of the candler.
Egg Shell thickness, the specific gravity of intact egg, percentage of shell present in the egg are important parameters for evaluating the strength of the shell. Shell strength is an efficient important trait as weak shelled eggs may cause considerable losses during handling and transport for marketing purposes due to breakage.
The normal shell thickness of chicken egg is 0.30 to 0.50 mm. The specific gravity of intact egg: It can be determined by the brine flotation technique. The eggs are to be permitted to
2) Internal Egg Qualities
Evaluation of Internal egg qualities include conditions of the air cell, albumen, and yolk. These indicators of intact eggs can be evaluated by means of candling for commercial purposes.
with the help of candling of eggs, i.e., passing white light through the egg contents shadow is emitted by the yolk and air cell. The shadow signalizes the size of the air cell, position of yolk, condition of vitelline membrane and condition of albumen.
Air cells – may be larger or smaller.
Yolk – may be a central position or away from the center.
Vitelline membrane – weak if the shadow of egg yolk becomes smooth.
Albumen – if the shadow of egg yolk is darker and it moves freely, there is thinning of thick albumen.
Air cell – Height in the freshly laid egg is 3.2mm and placed at the broader end of the egg.
Yolk – Centrally located; outline invisible, free from blood spot or meat spot (i.e., free from the shadow of foreign bodies).
Albumen -Transparent, thick and completely firm, free from blood spot or meat spot.
Air cell deepness: Depth of the air cells is to be measured with the help of scale.
Air cell deepness of eggs of various ages are-
Freshly laid egg 3.2mm
3 days old egg 6.4mm
15 days old egg 15.9mm
the shallowness of air cell up to 4mm is graded as ‘A’ and up to 8mm as ‘B’.
Manual on Avian Production and Management by Dr. Nilotpal Ghosh & Dr. Rajarshi Samanta