Processing & Evaluation of Egg Quality Flashcards
Main Parts of Egg
• Shell: It forms the protective covering of inner contents of the egg along with the two membranes.
• Shell membranes: within the shell are inner and outer membrane-porous and composed of fibres.
• Egg white: thin white and thick white.
• Egg yolk: The yolk is enclosed in a sac called the vitelline membrane.
• The chalazae appears as small twisted ropes of thickened white.
Composition of eggs
• Rich in protein, low in caloric value-to curb obesity and other health problems.
• Egg protein - high biological value.
• Used as a standard for measuring the quality of other food protein.
• Eggs are also known for their vitamin content.
• Vitamins A, D, and E are mainly concentrated in the yolk protein
• Eggs are also known for their fatty acids - saturated and unsaturated.
Processing of eggs
1) Collection
2) Handling & Washing
3) Grading & Candling
4) Quality Control Test
5) Quality Control & Standardization
6) Packaging & Marketing
Collection (Eggs)
• Belt conveyors are used for collecting and conveying the eggs.
• Frequent collection of eggs is an important factor for maintaining its quality.
• The frequency of collection of eggs should be at least three times a day.
Handling (Eggs)
• Important step to maintain its quality.
• To minimize the problem of damage.
• Use of clean and cool containers while handling.
Washing (Eggs)
• Individual eggs are grasped by small suction cups and placed on to another conveyor.
• Eggs is then moved by the conveyor into the cleaner.
• All eggs in the United States are washed in warm water with a mild detergent in order to remove any contaminants (manure, grease, blood, yolk, etc.) before they are sold for human consumption.
Cleaning and Grading (Eggs)
• They are rotated as brushes and water jets move carefully across the eggs.
• A fan then dries the egg.
• Eggs that are not cleaned or contain defects are removed from the processing line and are not packaged for human consumption.
• The cleaned eggs are graded in a candling booth, which is a dark cubical room.
• A penetrating light is shined on the eggs in order to grade them.
Candling (Eggs)
• Candling is a technique that allows a view of the shell
and inside of eggs without breaking the shell; double
yolks and so forth may be seen.
• Candlelight was once used for inspecting the interior of
eggs, where egg contents could be seen when held up
to a candle while being rapidly rotated.
• Today, commercial eggs may be scanned in mass, with
bright lights under trays of eggs.
Letter Grades (Eggs)
• Letter grades are based on candled quality and may appear as shields on the egg cartons.
• Grade shields on the carton indicate that the eggs were graded for quality and checked for size under the supervision of a trained packer.
• The USDA assigns a grade of “AA” to the highest quality egg. Even this high quality may quickly diminish if eggs are exposed to improper storage conditions
AA grade
• A thick white, prominent chalazae cord.
• A yolk must be round, high, and free from apparent defects. A flattened yolk indicates that the vitelline
membrane has weakened with age or by poor storage conditions.
• An air cell that may not exceed 1/8 inch in depth.
• A shell that must be clean and unbroken.
A grade
• An egg white is clear, reasonably thick, and stands high.
• The yolk must be practically free from apparent defects.
• The air cell must not exceed 3/16 inch in depth.
• The shell must be unbroken.
B grade
• Cover a wider area when broken open and are thinner and more flattened, possibly containing blood spots.
• Contain a yolk that may be slightly flattened and enlarged.
• Have an air cell size that exceed 3/16 inch in depth.
• Have a shell that must be unbroken and show no adhering dirt.
Air cell (Eggs)
• The air cell, also known as the air sac or air pocket, is the empty space formed at the large end of the egg.
• By definition, it holds oxygen.
• Initially, there either is no air cell or a small one.
• Then it becomes large and apparent to the eye when the warm egg cools, the egg contents shrink.
• The air cell increases in size with age, cooling, and moisture loss. It could result in microbial spoilage due to the plentiful oxygen it supplies to microorganisms.
Interior quality of egg: condition of yolk
• Fresh eggs
❖Yolk of fresh eggs are slightly acid pH, 6-6.2, and as there is increased loss of carbon dioxide, alkalinity is increased.
❖The pH of the eggs may be kept lowered or less alkaline during storage if the egg shells are coated with thin layer of oil.
• Deteriorated egg
❖The yolk takes up water from the white and the yolk membrane (i.e.,vitelline membrane stretches and when broken on to a plate, the deteriorated egg flattens and tends to spread over the plate.
❖Thus, separation of the yolk from the white is difficult or impossible.
Interior quality of egg: condition of albumen
• Fresh eggs
❖When broken the egg on to a plate, the albumen stands up in rounded form due to the viscosity of the thick portion of the egg albumen that surrounds the yolk.
• Deteriorated egg
❖As egg deteriorates, the percentage of the thin white increases due to proteolysis, reduction of S-S bonds, and interaction of mucin and lysozyme.
❖The increase in thinning correlates with an increase in alkalinity and alkaline hydrolysis of the disulphide bonds of ovomucin to yield a lower
molecular weight protein.
❖As the quality deteriorates, the pH of white increases from 7.6 to 9.7.
