Eggs and Processing of Eggs

Question 1

Groups of properties determining egg quality

Answer 1

Egg size / egg weight

Quality of the eggshell

Quality of the egg content

Question 2

Swiss egg weight classes

Answer 2

Small eggs (S): < 53 g
Normal eggs (M): >= 53 g
Large eggs (L): >= 63 g
Extra large eggs (XL): >= 73 g

Question 3

Measurement of the ggshell quality

Answer 3

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

Question 4

Crack detector

Answer 4

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

Question 5

Types of eggshell quality defects

Answer 5

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

Question 6

Light crack eggs

Answer 6

Low shell stability

Eatng quality ok, discarded

Question 7

Nicked eggs

Answer 7

Reason and occurrence:
Low shell stability, type of housing, diseases

Eating quality ok, cannot be stored

Question 8

Broken eggs

Answer 8

Reason, occurrence:
Low shell stability, type of housing, diseases

Eating quality: not for use

Question 9

Dirty eggs

Answer 9

Reason, occurrence:
Type of housing, bad hygiene

Eating quality: ok, short shelf life

Question 10

Damaged cuticula

Answer 10

Reason, occurrence:
Dirt, nickings, washing of the eggs

Eating quality: ok, short shelf life

Question 11

Mis-shaped eggs

Answer 11

Reason, occurrence:
Diseases, genetics, low consumer acceptance and difficult to sort

Eating quality: ok

Question 12

Soft shelled eggs

Answer 12

Reason, occurrence:
Ca deficiency, start of laying, age, metabolic diseases

Eating quality: not edible

Question 13

Flowing eggs

Answer 13

Reason, occurrence:
Ca deficiency, start of laying, age, metabolic diseases

Eating quality: not edible

Question 14

Undesired eggshell colour

Answer 14

Reason, occurrence:
diseases, intoxifications

Eating quality: ok?, low acceptance

Question 15

Washing eggs before selling

Answer 15

undesired by big retailers

Reasons:
Masking of microbial load by dirt & temperature during wahsing affects egg content

Dry cleaning is allowed

Question 16

Eggs with dents

Answer 16

two eggs are formed together -> shell of the later egg is dented
s. 30

Question 17

Genetic modification of eggshell stability

Answer 17

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

Question 18

Modification of eggshell quality by feeding

Answer 18

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

Question 19

Modification of eggshell quality by housing conditions

Answer 19

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)

Question 20

Eggshell colour

Answer 20

Colour types (genetically determined):
white, brown, blue-green, pink

Colour quality in brown-shelled eggs:
ideal: intensiv and creamy, homogenous, no freckles (?), rather dark

Question 21

Genetic determination of brown eggshell colour quality

Answer 21

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)

Question 22

Effects of feeding in brown eggshell colour quality

Answer 22

small effects (exception: wrong dosage of coccidiostatics)

Question 23

Effects of housing conditions in brown eggshell colour quality

Answer 23

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

Question 24

Properties describing the quality of the egg content

Answer 24

Nutritional quality

Sensory quality

Egg age

Quality defects of the egg content

Processing quality

Question 25

Modification of egg content with storage period, cause and measurement

Answer 25

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)

Question 26

Measurement traits describing physical properties of egg white and yolk in eggs

Answer 26

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

Question 27

Modification of egg content with storage period - Old taste

Answer 27

Cause: Changes in yolk lipids, cleavage of phosphatids, formation of aldehydes, increase of organic acids

Measurement: Organoleptic test

Question 28

Modification of egg content woth storage period - Elevation of the yolk

Answer 28

Cause: lower yolk density

Measurement: Screening (candling lamp)

Question 29

Midification of egg content with storage period - Occurrence of free amonia, amino acids, phosphorus

Answer 29

Cause: Microbial degradation

Measurement: Chemical analysis

Question 30

Modification of egg content with storage period - Decay

Answer 30

Cause: Microbial degradation

Measurement: Smell (e.g. H2S), appearance

Question 31

Quality defects of egg white and yolk

Answer 31

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

Question 32

Egg products

Answer 32

Entire egg, egg white, egg yolk:
- form: liquid, pulverised, frozen
- low-cholesterol products

Individual proteins:
- Lysozyme, foreign proteins (“molecular pharming”) and antibodies

Question 33

Scheme of egg processing

Answer 33

P. 95

Question 34

Minimal conditions to be fulfilled for egg products

Answer 34

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)

Question 35

Raw egg properties

Answer 35

High freshness and hygienic quality (shelf life)

Low eggshell proportion and high breaking strength

High egg yolk proportion (high dry matter content)

Question 36

Processing properties

Answer 36

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

Question 37

Foaming ability of the egg white

Answer 37

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)

Question 38

Factors of influence on foaming ability of the egg white

Answer 38

Genetic determination
Feeding effects
Effects of husbandry
Effects of egg processing

details see p. 108

Question 39

Emulsifying capacity of the egg yolk

Answer 39

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

Answer 40

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)

Question 41

General heating properties of eggs

Answer 41

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

Question 42

Green yolk discoloration in cooked eggs

Answer 42

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