EGG QUALITY PARAMETERS

Egg Quality Parameters

Anatomy of the Egg

  • Yolk: Yellow portion of the egg.

    • Color varies with the hen's diet.

    • Major source of vitamins, minerals, and fats.

  • Albumen (Egg White):

    • Comprises approximately 60% of the total egg weight.

    • Thin albumen is nearest to the shell; thick albumen stands higher and contains riboflavin and protein.

    • Total solids content is around 11-12%.

  • Germinal Disk:

    • Located on the yolk's surface; where fertilization occurs.

  • Chalazae:

    • Twisted, cordlike strands of egg white that anchor the yolk at the center of the egg.

    • Prominent chalazae indicate freshness.

  • Air Cell:

    • Pocket of air formed at the large end of the egg due to the contraction of contents during cooling.

    • Size increases as the egg ages.

  • Shell:

    • Outer covering of the egg, mainly composed of calcium carbonate and minor amounts of magnesium carbonate, calcium phosphate, and organic matter.

    • Colors range from white to brown depending on the chicken breed; color does not affect quality.

  • Vitelline Membrane:

    • Membrane that holds the yolk contents.

Egg Composition and Quality

Nutritional Composition

  • Egg White (Albumen): 60% of total egg weight.

    • Total solids: 11-12%

  • Yolk: 30-33% of total egg weight.

    • Total solids: 50-52%

  • Shell: 9-12% of total egg weight.

    • Composition: 94% calcium carbonate, 1% magnesium carbonate, 1% calcium phosphate, and 4% organic matter.

Factors Affecting Internal Egg Quality

  1. Disease:

    • Diseases like Newcastle disease and infectious bronchitis can lead to watery albumen.

  2. Egg Age:

    • Weak and watery albumen appears as eggs age; loss of CO2 makes the contents more alkaline, affecting flavor.

  3. Temperature:

    • High temperatures lead to rapid internal quality decline.

  4. Humidity:

    • High relative humidity decreases water losses from the egg.

  5. Handling:

    • Rough handling may crack eggs and degrade internal quality.

  6. Storage:

    • Frequent collection and rapid cooling (ideally at 50°F/10°C) are advised.

    • Avoid storage above 60°F (15.5°C) to prevent water loss; higher humidity (>70% RH) helps maintain freshness.

Physical Egg Quality Tests

  • Various tests used to determine egg quality include:

    • Whole Egg Tests: overall inspections.

    • Candling: light examination to detect defects.

    • Haugh Unit: measurement of albumen height.

    • Specific Gravity: assessing potential floating.

    • Component Tests: focusing on yolk index, color, and vitelline membrane strength.

Haugh Unit

  • A measure of egg protein quality based on the thickness of the albumen.

  • Haugh Unit Formula: HU = 100 \times log_{10}(h - 1.7w^{0.37} + 7.6)

    • Where:

    • h = observed height of the albumen (mm)

    • w = weight of the egg (g)

  • Haugh Unit Ratings:

    • AA: 72 or more

    • A: 60-71

    • B: 31-59

    • C: 30 or less

USDA Descriptors for Egg Quality

  • Clear: Free from discolorations or foreign bodies.

  • Firm (AA quality): Thick white that prevents yolk definition during twirling.

  • Reasonably Firm (A quality): Moderate thickness allows yolk outline to show slightly.

  • Weak and Watery (B quality): Thin white showing clear yolk outline.

Egg Nutrients


  • Percentage of Nutrients Found in Yolk vs. White:

    Nutrient

    Yolk (%)

    White (%)


    Energy

    76

    24


    Protein

    42

    58


    Choline

    100

    0


    Riboflavin

    33

    67


    Vitamin B12

    100

    0


    Folate

    96

    4


    Vitamin D

    100

    0


    Vitamin A

    100

    0


    Vitamin B6

    100

    0


    Iron

    100

    0


    Vitamin E

    100

    0


    Selenium

    59

    41


    Phosphorous

    93

    7


    Zinc

    100

    0


    Total Fat

    100

    0


    Cholesterol

    100

    0

    Egg Shell Problems

    1. Cracks due to excess pressure

    2. Cracks due to thin shells

    3. Body-checks

    4. Pimpled or toe holes

    5. Shell-less eggs

    Egg Defects via Candling

    • Common defects identified during candling include:

      • Prominent stains

      • Blood spots

      • Meat spots

      • Pressure cracks

      • Thin shell cracks

      • Body-checks

      • Pimpled eggs

      • Toe holes

    Typical Defect Rates

    • In 97% of AA-quality eggs:

      • 2.13% stains

      • 0.85% blood spots

      • 0.85% meat spots

      • 61% pressure cracks

      • 9.8% thin shell cracks

      • 6.8% body-checks

      • 13.6% pimpled eggs

      • 5.1% toe holes

    Consumer Egg Grades

    • AA Quality:

      • Clean, unbroken shell; firm white; yolk free of defects; Haugh unit > 72

    • A Quality:

      • Clean shell; clear and reasonably firm white; yolk must be free from apparent defects; Haugh unit 60-72

    • B Quality:

      • May have slight stains; weak and watery white; yolk may have small defects; Haugh unit < 60

    Anti-Nutrients in Raw Eggs

    • Avidin: Binds biotin (a B vitamin), making it unavailable for absorption.

      • High intake of raw egg whites could lead to biotin deficiency.

      • Cooking denatures avidin, preventing nutrient depletion.

    Yolk Color Influencers and Measurements

    • Carotenoid Sources:

      • Grass, corn, marigold petals, and paprika influence yolk coloration.

      • Different carotenoids have various deposition rates and impacts on yolk color.

      • Measurement involves color scales (e.g., Hunterlab).

    Conclusion

    • Understanding egg quality parameters is crucial for production, marketing, and nutritional assessments of eggs. Knowledge on how to improve egg quality via yolk color adjustment and nutritional content enhances consumer satisfaction and safety.