Eggs and Processing of Eggs Flashcards
Groups of properties determining egg quality
Egg size / egg weight
Quality of the eggshell
Quality of the egg content
Swiss egg weight classes
Small eggs (S): < 53 g
Normal eggs (M): >= 53 g
Large eggs (L): >= 63 g
Extra large eggs (XL): >= 73 g
Measurement of the ggshell quality
Shell stability
- breaking strength, elsaticity, shell thickness
- Crack detector, determination of the proportions of broken eggs, electronic egg
Eggshell quality defects
- visual examination, determination of the format index
- screening by UV light (candling lamp, table or automatic device): detection of eggs with “light” cracks, blood and meat spots, and fertilized, hatched eggs
Crack detector
Technology for use in automatic eggshell quality testing
Egg is taped with tiny, electronically controlled hammers
Tiny microphones are installed in the hammers
Computer software to analyse the sounds: Eggs with suspicious sound patterns are removed
Types of eggshell quality defects
Light crack eggs
Nicked eggs (inner membrane intact)
Broken eggs (Content flows out)
Dirty eggs
Damaged cuticula
Mis-shaped eggs (too oval, differing thikness, appositions)
Soft shelled eggs
Flowing eggs ((partially) without shell)
Undesired eggshell colour
Light crack eggs
Low shell stability
Eatng quality ok, discarded
Nicked eggs
Reason and occurrence:
Low shell stability, type of housing, diseases
Eating quality ok, cannot be stored
Broken eggs
Reason, occurrence:
Low shell stability, type of housing, diseases
Eating quality: not for use
Dirty eggs
Reason, occurrence:
Type of housing, bad hygiene
Eating quality: ok, short shelf life
Damaged cuticula
Reason, occurrence:
Dirt, nickings, washing of the eggs
Eating quality: ok, short shelf life
Mis-shaped eggs
Reason, occurrence:
Diseases, genetics, low consumer acceptance and difficult to sort
Eating quality: ok
Soft shelled eggs
Reason, occurrence:
Ca deficiency, start of laying, age, metabolic diseases
Eating quality: not edible
Flowing eggs
Reason, occurrence:
Ca deficiency, start of laying, age, metabolic diseases
Eating quality: not edible
Undesired eggshell colour
Reason, occurrence:
diseases, intoxifications
Eating quality: ok?, low acceptance
Washing eggs before selling
undesired by big retailers
Reasons:
Masking of microbial load by dirt & temperature during wahsing affects egg content
Dry cleaning is allowed
Eggs with dents
two eggs are formed together -> shell of the later egg is dented
s. 30
Genetic modification of eggshell stability
Heritabilities (breaking strength, crack detector resonance): 0.3 - 0.6
Heterosis effects: small
Genetic variablitiy: high between origins, still present between breeding lines
Slight decline with increasing level of performance (egg size, egg number)
Decline with processing laying period
Improvement after moult
Modification of eggshell quality by feeding
Decline of eggshell stability in case of deficiency of:
- Calcium
- Vitamin D3
- Phosphorus
- Magnesium, manganese, further trace elements
- Calcium and manganese in the rearing phase of the hens
Decline of eggshell stability in case of excess of:
- Phosphorus
- Chloride
Increase of eggshell quality when offering minerals in a favourable manner:
- ad libitum access
- coarse
- offer in the evening
- offer by choice feeding
Modification of eggshell quality by housing conditions
Avoid impairment by inappropriate lighting regimen and too high ambient temperatures
Type of husbandry: same breaking strength; broken eggs: cage > floor, outside stay
Impairment with different diseases (newcastle disease, metabolic diseases)
Eggshell colour
Colour types (genetically determined):
white, brown, blue-green, pink
Colour quality in brown-shelled eggs:
ideal: intensiv and creamy, homogenous, no freckles (?), rather dark
Genetic determination of brown eggshell colour quality
Heritabilities: 0.4 - 0.6
Genetic variability between breeding lines and within lines available
Almost no relationship to laying performance and egg size (= independent breeding goal)
Effects of feeding in brown eggshell colour quality
small effects (exception: wrong dosage of coccidiostatics)
Effects of housing conditions in brown eggshell colour quality
likely higher frequency of discoloration:
- at high ambient temperature and in the morning
- with various of diseases and with stress
- colour intensity may decline with processing laying period
Properties describing the quality of the egg content
Nutritional quality
Sensory quality
Egg age
Quality defects of the egg content
Processing quality
Modification of egg content with storage period, cause and measurement
Air chamber height (increase)
Cause: water loss through shell
Measurement: Screening (Candling lamp)
pH (increase in egg white)
Cause: CO2 diffusion through shell
Measurement: pH meter
Density (decline)
Cause: Water loss through shell
Measurement: Areometer, salt, solution, dry matter content, weight loss
Viscosity of egg white (decline)
Cause: Ovomucin liquefaction
Measurement: Egg white height/index, Haugh units, viskosimeter, refractometer, foam forming device
Egg white texture (change)
Cause: Ovomucin liquedaction
Measurement: Optical grading
Diffusion processes (egg white <-> yolk, osmotic porcesses)
Cause: Water diffusion: white -> yolk, Phosphate diffusion: yolk -> white
Measurement: Visual grading
Yolk membrane stability (decline)
Cause: Egg yolk deswelling
measurement: Yolk height, yolk index, yolk membrane stability (texture analyser)
Measurement traits describing physical properties of egg white and yolk in eggs
Egg white height, mm = average height of the egg white in about 1 cm distance from the yolk
Egg white index, promille = egg white height x 1000 / average egg white diameter
Haugh Units = 100 x log(egg white height - 1.7 x egg white^0.37 + 7.6)
Yolk index, % = yolk height x / yolk diameter
Modification of egg content with storage period - Old taste
Cause: Changes in yolk lipids, cleavage of phosphatids, formation of aldehydes, increase of organic acids
Measurement: Organoleptic test
Modification of egg content woth storage period - Elevation of the yolk
Cause: lower yolk density
Measurement: Screening (candling lamp)
Midification of egg content with storage period - Occurrence of free amonia, amino acids, phosphorus
Cause: Microbial degradation
Measurement: Chemical analysis
Modification of egg content with storage period - Decay
Cause: Microbial degradation
Measurement: Smell (e.g. H2S), appearance
Quality defects of egg white and yolk
Blood and meat stains
Yolk stains
‘Trace eggs’
‘Candling lamp eggs’
Bacterial contamination
‘Putrid eggs’
‘Hay eggs’
Mouldy eggs
Yolk discoloration
Egg in egg (2 shells and 2 egg whites)
‘Spare eggs’ (no yolk)
Double yolk
Deviations in egg white structure
Cloudy blurring of the egg white
-> p. 78, 85, 88 for details
Egg products
Entire egg, egg white, egg yolk:
- form: liquid, pulverised, frozen
- low-cholesterol products
Individual proteins:
- Lysozyme, foreign proteins (“molecular pharming”) and antibodies
Scheme of egg processing
P. 95
Minimal conditions to be fulfilled for egg products
Pasteurisation, if not subjected to another heat treatment
If pasteurised, cooling to maximal +5°C directly after heating required
No mixing of eggs of different animal species
For liquid products, the conditions of sale are the same as for marketing of shell eggs (broken eggs can not be used)
Raw egg properties
High freshness and hygienic quality (shelf life)
Low eggshell proportion and high breaking strength
High egg yolk proportion (high dry matter content)
Processing properties
Good foaming properties / baking quality (egg white)
High emulgation forming ability (yolk)
High cooking stability and easy shell removing properties after cooking
Limited discoloration of the yolk after cooking
High heat stability during manufacturing of the egg products
Foaming ability of the egg white
Importance: Improvement of baking quality (shaping effect, binding ability, loosening effect, e.g. bubbles in bread)
Assessment methods:
- indirect: egg weight height/ Haugh units, viscosity, lysozyme activity
- foam formation ability (foaming index = multiple of initial volume) and foam stability (eluate after a given time), devices: foam forming device, kitchen mixer, shaker with sieve, N2 gassing through glass filter
- Binding ability and baking properties (extension and firmness of sample bakeries)
Factors of influence on foaming ability of the egg white
Genetic determination
Feeding effects
Effects of husbandry
Effects of egg processing
details see p. 108
Emulsifying capacity of the egg yolk
Importance:
Baking properties, natural emulsifyer for food processing
Measurement:
Emulsion stability (drainage from an emulsion of yolk, maize germ oil and water)
Factors of influence:
- Content of lipoproteins -> differences in origins and lines; repeatability 0.5-0.6
- Improvement with progressing stage of laying period
- Egg age: trend for a decline
- Emulsifying properties: egg yolk proportion, method, decline with egg white contamination and pasteurisation
Importance:
Most important processing property for cooking suitability; certain importance for liquid egg processing
Measurement:
Determination of time for shell removal & proportion of damaged surface (difficult to standardise)
Improvement:
- Use of older eggs (increase in pH, fewer connection points between shell and egg white)
- Longer cooking time
- Use vapour pressure or at least put eggs into already cooking water
- Cooling by cold water
Measures against shell damage during cooking:
- Picking before cooking (easier removal of hot air and, especially, reducion of tension in disturbance of the eggshell structure)
- Incubating the egg in vinegar before cooking (dissolves crystals and smothes structure)
General heating properties of eggs
Importance:
Pasteurisation without coagulation of the proteins of the egg white (84.5°C) and yolk (65°C)
Cooking of shell eggs: egg white absorbs thermic energy until it is coagulated before the full heat reaches the yolk
Measurement:
e.g., observation of the time needed for coagulation at defined temperature
Factors of influence:
not yet investigated
Green yolk discoloration in cooked eggs
Reason:
FeS (green) formed from Fe and H2S; S from protein (sulphur-containing amino acids)
Importance:
Discoloration in heated egg products and long-cooked coloured eggs produced for Easter
Alleviation (Linderung):
Less pronounced in fresh eggs and in eggs cooked not too long; addition of acid to liquid eggs
