Comprehensive Notes on Eggs

Egg Structure

  • 5 Major Structural Components:
    • Shell
    • Yolk
    • Latebra
    • Germinal Disc
    • Vitelline (Yolk) Membrane
    • Chalazae
    • Air Cell
    • Shell Membranes
    • Chalazae
    • Chalaziferous Layer
    • Thin Albumen (White)
    • Thick Albumen (White)

Yolk

  • Approximately 30% of the egg's weight.
  • Nutritionally dense part of the egg.
  • Anchored in the center by chalazae, which are twisted strands of albumen.
  • The hen's diet determines the color of the yolk.
  • Artificial colors are not allowed in egg production.

Egg White (Albumen)

  • Makes up about 60% of the egg's weight.
  • Two types:
    • Thick albumen: Located around the yolk.
    • Thin albumen: Located around the thick albumen.
  • Three main types of protein in the albumen:
    • Ovalbumin: 54% of the protein; gels well, and denatures easily when heated.
    • Conalbumin: 13% of the protein; protects against bacterial contamination by binding iron which bacteria need to grow.
    • Ovomucoid: 11% of the protein; does not denature.
  • Avidin is present in very small amounts; binds biotin (a B vitamin), which is a reason why raw egg consumption is discouraged.

Shell

  • About 12% of the egg's weight.
  • Composed of calcium carbonate.
  • Porous, allowing gas exchange between the inner egg and the atmosphere.
  • The hen's breed determines shell color.
  • Brown eggs are not necessarily more nutritious or tasty than white eggs; color is breed-specific.
  • The shell has a natural coating which is removed during processing in the US.

Shell Membranes and Air Cell

  • Inner and outer membranes exist between the albumen and the shell.
  • Membranes provide protection against bacterial contamination.
  • The air cell is located between these two membranes, usually at the larger end of the egg.

Large Egg Nutrition - Macronutrients

  • Calories: 75 per large egg (60 from yolk, 15 from white).
  • Protein: 7 grams of complete protein.
    • 4 grams from the white.
    • 3 grams from the yolk.
    • High-quality protein, considered a reference protein.
  • Fat: 5 grams in the egg yolk, none in the egg white.
  • Cholesterol: 186 mg (two eggs provide the Daily Value (DV) for cholesterol).
  • Carbohydrate: Very little.

Large Egg Nutrition - Micronutrients

  • Vitamins:
    • Yolk: Fat-soluble vitamins A, D, E, K.
    • White: Water-soluble B vitamins.
  • Minerals: Zn (Zinc), Se (Selenium), I (Iodine), Fe (Iron).
    • Iron is less available due to protein binding.
  • Phytochemicals: Xanthophylls such as Lutein and Zeaxanthin.

Regulation and Inspections

  • 1970 Egg Products Inspection Act.
  • All processing facilities are inspected by the USDA Poultry Division.
  • This applies whether the sale is intra or inter-state.
  • Grading is voluntary and paid for by the producer.
  • Grocery stores typically sell only grades AA and A.

Three Grading Methods

  • Candling: A non-invasive measure where eggs are rotated over a light to evaluate inner contents.
    • Quality indicators:
      • Yolks well suspended by the chalazae.
      • Small air cell.
      • Absence of contaminants (e.g., blood spots).
  • Invasive measures:
    • Haugh Units: Analytical assessment of albumen thickness.
    • Physical Evaluation: Subjective assessment of albumen thickness.

Value-Added Eggs

  • Marketing term with no official definition.
  • Special attributes due to nutrient content or hen's environment.
  • High omega-3 fatty acid eggs: Originate from hens fed a diet enhanced with Omega-3 Fatty Acids (according to the USDA).

Cage-Free Eggs

  • United Egg Producers (UEP): A co-op representing 95% of US egg production.
  • UEP Set guidelines in 2006:
    • Dedicated nests for laying eggs.
    • Perches for hens to rest.
    • Vertical and lateral movement allowed.
    • Continuous access to food and water.
    • Access to a litter area for scratching, foraging, and dust bathing.

USDA Definition of Cage-Free Eggs

  • Eggs packed in USDA grademarked consumer packages labeled as cage-free must be produced by hens housed in a building, room, or enclosed area that allows for unlimited access to food, water, and provides the freedom to roam within the area during the laying cycle.

USDA Definition of Free-Range Eggs

  • Eggs packed in USDA grademarked consumer packages labeled as free-range must be produced by hens housed in a building, room, or area that allows for unlimited access to food, water, and continuous access to the outdoors during their laying cycle. The outdoor area may be fenced and/or covered with netting-like material.

Egg Sizing

  • Eggs are sorted by size into 6 weight classes.
  • Recipes are typically based on large-size eggs.
  • Egg size substitutions:
    • Two large eggs = two medium eggs
    • Three large eggs = three medium eggs
    • Four large eggs = five medium eggs
  • Sizing is not an indicator of quality.

Importance of Size to Pricing or Cooking

  • Economic consideration: Compare the cost of medium versus large eggs.
  • If one dozen medium eggs costs 0.15 less than one dozen large eggs, buying medium eggs is more economical; vice versa if they cost 0.15 more.

Determining Egg Freshness

  • The contents of the egg become more alkaline as it ages.
  • The air cell of the egg increases in size.
  • The albumen thins in viscosity.
  • When cracked, the yolk of an older egg is not centered due to weakening chalazae.

Safely Handling Eggs

  • Maintain refrigerated temperatures at all times.
  • Cook to a proper temperature of 145°F (FDA recommended) until the white is completely coagulated and the yolk has begun to thicken.
  • Use eggs in the shell within 3 weeks.
  • Avoid eating raw eggs.
  • Mishandling eggs can lead to Salmonella enteritidis infection.