History and Composition of Eggs

History of Commercial Egg Production

• Wild fowl were domesticated around 3200 B.C.
• Egyptian and Chinese records show fowl laying eggs for humans by 1400 B.C.
• Europe domesticated hens starting from 600 B.C.
• There is evidence of native fowl in the Americas before Columbus.
• Columbus' second trip in 1493 brought the first chickens to the New World from Asia.

Composition of Eggs

• Eggs have five main structural components: shell, shell membranes, air cell, albumen, and yolk.

Shell

• Primarily calcium carbonate (CaCO3)
• Rigid structure with 7,000 to 17,000 microscopic pores, making it semi-permeable to air and moisture
• Porosity aids in gas exchange and influences the egg's aging
• Shell color depends on the breed of the hen, which does not affect flavor, quality, or nutritional value.
• Acts as a physical barrier against bacterial contamination.

Natural Cuticle

• A thin, waxy layer that seals the pores
• Shields the egg from microorganisms
• Washing eggs removes the cuticle
• Refrigeration is necessary to prevent contamination.

Membranes

• Two beneath the shell include inner and outer layers
• Made of keratin
• Prevent bacteria from entering the egg.

Air Cell

• Forms between the two membranes as the egg ages
• Small when the egg is freshly laid.
• The air cell grows when moisture leaves the shell.
• Older eggs are more buoyant and float in water
• The size indicates age and is used in grading.

Albumen (Egg White)

• Makes up 60% of the egg's weight
• Consists of 90% water and 10% protein
• Proteins are responsible for foaming, binding, and coagulating.
• The most abundant protein is ovalbumin
• Other proteins include conalbumin, ovomucin, and lysozyme

Chalazae

• Twisted strands of albumen
• Anchors the yolk to center

Vitelline Membrane

• Surrounds the yolk
• Branches to form the chalazae
• Consists of a thin layer of albumen.

Thin Albumen

• Farther from the yolk
• Becomes more watery as the egg ages.

Yolk

• Makes up 30% of the egg's weight.
• Is the egg's primary source of nutrients: fats, proteins, vitamins, and minerals.
• Consists of roughly 50% water, 33% lipids, and 17% proteins.
• Lecithin is a fat-based emulsifying agent,
• Screened to ensure it is not fertilized
• Its color depends on the hen's diet.

Functions of eggs in foods

• Serves as a coagulant for proteins, a structure builder, provides moisture retention, is an emulsifying agent, creates foams, and is an interfering agent

Coagulation of Proteins

• Heat changes texture by protein denaturation
• Egg proteins, ovalbumin in whites and lipoproteins in yolks
• They unfold and lose their natural structure, forming new bonds when they coagulate
• Egg whites coagulate around 144-149°F (62-65°C)
• Egg yolks coagulate at about 149-158°F (65-70°C)

Structure Building

• Whites coagulate during baking, solidifying the structure of cakes, cookies, and bread
• Provide structure by creating a protein network that traps air and moisture
• Heat expands the air
• Proteins firm up, creating a light, airy texture
• Proteins unfold and gel together
• Thicken products like sauces and custards.

Moisture Retention

• Contributes moisture in baked goods, keeping them soft and tender.
• Egg yolks, high in fat and water, adds richness and moisture to batters and doughs.

Emulsifying Agent

• Lecithin has hydrophilic and hydrophobic ends
• Makes it ideal for forming stable emulsions.
• Recipes include mayonnaise, hollandaise sauce, or aioli.
• It binds oil, water, and vinegar into a smooth, homogenous mixture
• Forms a stable emulsion with thick, creamy textures.

Foaming

• Egg-white foams are essential for aerating and leavening
• Examples: meringue, angel food
• There is protein denaturation from vigorous beating of whites.
• Unfolded proteins form films around air cells, which expand when heated.
• Proteins coagulate and set the structure after expansion.
• Formation and stability depend on beating technique, temperature, and added ingredients.

Stabilizing Foams

• Acidic ingredients like Cream of tartar or lemon juice lowers the pH of egg whites
• Denatures protiens more easily
• Helps them bond more tightly.
• This creates a more stable foam that is less likely to collapse during cooking
• Sugar slows the unfolding of egg proteins, delaying foam formation and protecting against overwhipping.
• Sugar dissolves and syrups are too thick to drain.

Interfering Agent

• They interfere with the formation of large ice crystals in frozen desserts or sugar crystals in candies
• This creates a smoother, velvety texture

Color

• Yolks contribute to golden brown color
• Proteins contribute to Maillard browning.

Purchasing Eggs

• 1970 Egg Products Inspection Act mandates inspection of egg-processing plants.
• Ensures defective eggs are not sold to consumers.
• Enforced by the USDA Poultry Division.
• Consumers should look for cracks, fertilization, mold, blood, and off-color
• "Restricted eggs" fail inspection.

Restricted Eggs

• Identified by shipping container using “Restricted Eggs - For Processing Only In An Official USDA Egg Products Plant," for checks or dirties;
• Or “Restricted Eggs - Not To Be Used As Human Food," for inedibles, loss, and incubator rejects
• Or "Restricted Eggs - To Be Regraded" for graded eggs with more restricted eggs than allowed
• Checks has a broken shell or a crack in the shell, but the shell membranes are intact so that the egg contents don't leak.
• Dirties may have adhering dirt, prominent or conspicuous stains, or moderate stains covering more than one-fourth of the shell surface.
• Incubator rejects have been subjected to the incubation process for a period of time.
• Inedibles are moldy, musty or sour or exhibit rot, blood rings, green whites, stuck yolks or embryo chicks.
• Leakers have a crack or break in both shell and shell membranes so that the contents are leaking.
• Loss eggs are leakers, inedibles and any eggs that have been cooked, frozen or contaminated.

Grading

• Grading by the USDA is optional and paid for by the egg producer.
• USDA grades: AA > A > B
• Grade B is not sold directly to consumers but is used to make liquid, frozen, and dried egg products.
• Three methods for grading: candling, measuring Haugh units, and evaluating appearance.

Candling

• Was developed from holding an egg to the light of a candle to check contents
• They are mechanically rotated over lights on rollers.
• Whites become thinner with viscosity and are more transparent over time.
• Yolks appear as shadows
• They sit closer to the shell given that no longer held up by the chalazae

Haugh Units

• An egg is cracked open onto a flat surface
• The height of albumen is measured
• Fresh egg whites are tall and firm, older ones tend to spread out.
• Haugh unit is calculated by measuring albumen height to weight ratio and a conversion table.
• As Haugh unit decreases, qualities decreases.

Appearance

• Graded by based on their appearance broken flat onto a surface

• Quality eggs should have a thick albumen that is not spread

• Yolk should be upright and compact

• Quality decreases/flattens over time

• Eggs are sold in various sizes which are determined by their weight (minimum per dozen)

• Large eggs are mainly used in recipes

Egg Replacement

• One egg contains 215mg cholesterol
• Substitutes are made by eliminating/replacing the egg yolk (rich in cholesterol)
• Replacements can be vegetable oil
• These substitutes are ultra-pasteurized which allows for a longer shelf life
• This also alows them them to be added to uncooked foods
• Can have a high sodium level

Types of Eggs

• Chicken eggs are standard
• Standard eggs are white or brown-shelled non-fertilized eggs
• Fertilized eggs will not develop if refrigerated
• Free-range have acess to outdoor areas although there no definition of this
• Organic eggs come from uncaged hens that are fed an organic diet

Speciality Eggs

• Pickled eggs: Hard boiled, soaked in vinegar, often with beets
• Salted duck eggs: Chinese preserved food made by soaking duck eggs in brine
• Century eggs: Chinese delicatcy perserved by clay mixture for several weeks to months

Preparation of Eggs

• The preparation of eggs is affected by temperature and time
• It's key to keep temp low and/or reduce time
• Overheated proteins become tough and rubbery and shrink from dehydration
• Coagulation temperatures differ for whites and yolks (whites have temps the cool faster) but its still recommended to firm yolks and soft whites

Changes in prepared eggs

• Color changes occur when the eggs are overcooked or the temps are too high
• Sulfur may react with the egg white and turn it into ferrous sulfide
• This creates a green colored ring

Storage of Eggs

• Eggs lose quality quickly at room temperature
• During storage, the egg whites thin and the vitelline membrane degrades while the yolk flattens
• Futhermore the air cell get larger
• Fresher eggs wil sink unlike older eggs

Safety

• American's refigerate their eggs because salmonella is more prominent in their manufacturing plants

Extra Tips

• Keep eggs in cartons and fridge
• Eggs have pores so it is best to keep cool

Egg Products

• Eggs can be spray dried in powder whole and sepreately
• The Sugars are removed prior
• Made by rewetting instantly
• Shell life dried with unlimited
• Shell life whole limited to 1 year

Safety

• It's best to buy refrigerated eggs
• One should check the carton for clean eggs
• An egg seperator should be used to seperate yolk
• Eggshells shouldn't be in food products