Edible Eggs

Abeer Abdel-naser Awad Abdel-All

Items of lecture:

A. Changes occur after laying.

B. Egg quality (external and internal quality).

C. Egg freshness.

A-changes occur after laying

A- chemical changes: (aging)

The rate of deterioration is closely related to the

loss of CO2 through the shell and increase

alkalinity of egg contents.

The higher the temperature the higher the loss of

CO2.

• The pH of the white may rise from about 7.6

in a freshly laid egg to high as 9.0 to 9.7 within

few days (due to loss of CO2 ).

• The white become thinner, so spread more

when the egg is broken out.

Why the white become thinner?

• The rise in pH allows the electrostatic

complex between lyzozyme and ovomucin to

break.

• Breaking of disulphide bonds in ovomucin has

been suggested as a factor in the thinning of

egg white.

• The thinner white cannot withstand the yolk

centered in the egg. In addition the white

became yellow.

• The vitelline membrane which confines the

yolk stretches due to water passage from the

white to the yolk.

• The yolk becomes enlarged and flattened.

• The chalazae become detached allowing the

yolk to move freely within the egg.

• The free yolk may rest against the shell

leading to sided or stuck yolk or may be

ruptured leading to spreading yolk

• Air cell enlarged due to the water evaporates

from liquid contents through the shell pores

and the air replaces the water lost.

• The egg becomes extremely suitable for

invasion by microorganisms.

• B-Microbial changes:• Rot and mold:

These develop in some eggs by the presence of

microorganisms like bacteria, mold and yeast

within the egg.

• These organisms mainly enter the egg after

laying from dirty and moist shell. Washing

increase the case due to removal of the bloom

and help the microorganisms to invade the

egg contents through the pores.

• Rotten eggs:

• These eggs normally contain a mixed infection

of Gram-negative and a few Gram-positive

organisms also.

• Alcaligenes, Achrimobacter, Pseudomonase,

Serratia, Cloaca, Hafnia, Citrobacter, Proteus

and Aeromonase.

• Bacteria causing abnormal flavors (taint):

• Proteus vulgaris-------------- foul odor.

• Pseudomonase-------------- ammoniacal odor.

• Bacillus subtilis------------- H2S production.

• Eggs may pick up flavors from strange odors in

the storage area.

Organisms produce pigments

Organism Type of rot

Proteus sp.Black rot

Aeromonas liquefaciensBlack rot

Serratia marcescensRed rot

Pseudomonase maltophiliaGreen rot

Pseudomonase fluorescensFluorescent green changed to pink

Pseudomonase putidaFluorescent green rot

Pseudomonase aeruginosaFluorescent blue rot

FlavobacteriumYellow rot

AlcaligensColorless

• Mold spoilage:

• Less important than bacteria, only under

humid conditions the shell could be clothed

with mycelium “Whiskers”.

• Hyphae penetrate the pores and grow on the

shell membranes associated with gelling of

the albumen around patches of mycelia.

• On candling these show up as dark or colored

patches or rings.

• Further growth results in the complete gelling

of the albumen and the break down of yolk

membrane.

• Cladosporium and Sporotrichum the most

common types.

B- Egg quality

• Egg quality standards are based on:• Shell cleanliness.• Shell soundness. External • Shell texture.• Shell shape.• Relative viscosity of albumen.• Freedom from foreign matter in albumen. Internal • Shape and firmness of yolk.• Freedom from yolk defects.

What is Egg Quality?

Exterior egg quality – shell quality based on shell cleanliness, shell soundness, shell texture, shell shape.

Interior egg quality – based on relative viscosity of the albumen, freedom from foreign matter in the albumen, shape and firmness of the yolk, and freedom from yolk defects.

Judging Egg Quality

• External quality:Shell stability faultsCleanlinessAppearance faultsGrades- A, B, Loss

Controlling Egg Size

• In many markets, producing eggs that are above the size of large eggs holds

• no economic benefit. Larger eggs tend to have weaker shells

• and are more likely to be broken in transit due to current packaging

• materials and shapes.

Controlling Egg Size

• Factors that influence egg size:• Protein Intake, esp. Methionine and Lysine• Breed• Caloric intake• Linoleic acid levels in the feed• Body weight at the onset of production.

Internal egg quality (Broken-out Egg Quality)

• Shape and Uniformity of Albumen• Amount of Thick Albumen• Shape and Height of Yolk• Presence of Meat or Blood Spots– Less than 1/8 inch diameter = Grade B– More than 1/8 inch diameter = Inedible

Egg grading - exterior• Grade A – Clean, unbroken,

practically normal shape. Ridges and rough spots that do not materially detract from the appearance of the egg are ok.

• Grade B – Unbroken, clean to moderately stained (1/32 of surface if localized, or 1/16 of surface if scattered). Maybe somewhat unusual to misshapen, or show pronounced ridges or thin spots.

• Dirty – Unbroken. Adhering dirt or foreign material, prominent stains, or moderately stained if in excess of B grade.

Egg grading - interiorQuality factorGrade AAGrade AGrade B

Air cell1∕8 inch or less depth

3∕16 inch or less depth

Over 3∕16 inch depth

White Clear and firmClear and reasonably firm

Weak and watery. Small (< 1/8 inch diameter) blood and meat spots may be present

Yolk Outline slightly defined

Outline fairly well defined

Outline plainly visible, enlarged and flattened. May have clearly visible germ development but no blood.

A Grade AA egg will stand tall. The yolk is firm and the area covered by the white is small. There is a large proportion of thick white to thin white.

Grade A egg covers a relatively small area. The yolk is round and upstanding. The thick white is large in proportion to the thin white and stands fairly well around the yolk

A Grade B egg spreads out more. The egg yolk is flattened and there is about as much (or more) thin white as thick white

AA QualityAA Quality

High AA Average AA Low AA

A QualityA Quality

High A Average A Low A

B QualityB Quality

High B Average B Low B

Practice

Grade AAGrade AA

Practice

Grade AAGrade AA

Practice

Grade AAGrade AA

Practice

Grade InedibleGrade Inedible

Practice

Grade InedibleGrade Inedible

Practice

Grade InedibleGrade Inedible

Practice

Grade AGrade A

Practice

Grade AGrade A

Practice

Grade BGrade B

Practice

Grade BGrade B

Important functional and aesthetic Important functional and aesthetic properties of eggproperties of egg

1- act as a leavening agent in baked goods (texture of breads and cakes).

2- act as binding agent to hold other ingredients together.

3- act as a thickening agent (custards, puddings, etc.).4- albumen act as a smoothing agent to give icings a

desirable texture.

5- yolk contains lecithin (a natural emulsifier) which helps keeping fat and other ingredients in a uniform suspension.

6- eggs are used as a clarifying agent which are used to remove extraneous materials from beverages, coffee, etc.

7- eggs are used as a coating for cakes, rolls, cookies, etc.

8- yolks add color and richness to foods.9- eggs tend to take up flavors and odors of

surroundings.

Egg handling for quality preservation

1. by frequent gathering.2. by careful handling & proper cooling.3. by holding under controlled humidity.4. by proper packaging. 5. by frequent marketing.6. by moving eggs rapidly through marketing

channels.7. by proper care of eggs at home.

C- Egg freshness

The ideal conditions that keeping eggs so long fresh and of good quality are:

-Temperature that don’t go above 4oC.-Relative humidity 70-80%.-Proper handling.

Testing egg for freshness

A) Egg shell:On small scale:a) Brine solution: 10% NaCL solution but

actually it is used to determine shell thickness.

b) Shaking test: fresh egg emit no sound, while old egg will emit sound due to thin albumen and loose chalazae and free yolk.

c) Ultra-violet rays: using Quartz lamp fresh egg give pink color due to reaction between UV rays and ooporpherin pigment in the bloom, while old egg give violet color due to reflection of UV on surface of an egg.

N.B.:Disadvantages : it depends on the presence of

bloom which may be lost due to: aging after 14 days or, washing, or brushing, or bad handling. This test is restricted to white shell eggs only.

On large scale:Only one method to detect freshness without

breaking eggs “candling “.Tow types of candling either individual candling

or mass candling.In individual candling the egg is hold and the

broad end upper most to measure the air cell using the egg caliber as increase its volume exceeding 3mm. means old egg.

In mass candling rows of egg is tested.

Individual candling

““candling an eggcandling an egg””

Measuring Air Cell DepthMeasuring Air Cell Depth

Mass candling

B) Broken out appearance: Egg contentsFresh egg:Normal odor, yolk stand up well centrally by the

albumen, yolk color is even yellow, no mottling or foreign bodies.

Both chalazae are distinct and firmly attached to yolk.

Albumen is clear with no taint or color, both thick and thin are distinct, no blood, no bodies.

Germinal disc is just visible

Old egg:Abnormal odor may be present.Thick albumen is not apparent.Chalazae become detached and very weak.Yolk is displaced, flattened and severely patched

or mottled.Blood or meat spots may present.