Eggs as food
An egg is a body consisting of an ovum surrounded by layers of membranes and an outer casing of some type, which acts to nourish and protect a developing embryo. Most edible eggs, including bird eggs and turtle eggs, consist of a protective, oval eggshell, the albumen (egg white), the vitellus (egg yolk), and various thin membranes. Every part is edible, although the eggshell is generally discarded. Nutritionally, eggs are considered a good source of protein.
Roe and caviar are edible eggs produced by fish.
Egg uses as food ingredients
Bird eggs are a common food source. The most commonly used bird eggs are those from the chicken, duck, and goose, but smaller eggs such as quail eggs are occasionally used as a gourmet ingredient, as are the largest bird eggs, from ostriches. Most commercially produced chicken eggs intended for human consumption are unfertilized, since the laying hens are kept without any roosters. Fertile eggs can be purchased and eaten as well, with little nutritional difference. Fertile eggs will not contain a developed embryo, as refrigeration prohibits cellular growth.
Chicken eggs are widely used in many types of cooking. Dishes that use eggs range from both sweet to savoury dishes. Eggs may be pickled; hard-boiled, scrambled, fried and refrigerated; or eaten raw, though the latter is not recommended for people who may be susceptible to salmonella, such as the elderly, the infirm, or pregnant women. In addition, the protein in raw eggs are only 51% bio-available, whereas a cooked egg is nearer 91% bio-available, meaning the protein of cooked eggs is nearly twice as absorbable as the protein from raw eggs.[1]
A boiled egg can be distinguished from a raw egg without breaking the shell by spinning it. A hard-boiled egg's contents are solid due to the denaturation of the protein, allowing it to spin freely, while the inertia of the liquid contents of a raw egg causes it to stop spinning within approximately three rotations.
White
The albumen, or egg white contains protein but little or no fat. It is used in cooking separately from the yolk, and can be aerated or whipped to a light, fluffy consistency. Beaten egg whites are used in desserts such as meringues and mousse.
Eggshell
Ground egg shells are sometimes used as a food additive to deliver calcium.
Boiled eggs that are difficult to peel are usually too fresh. Fresh eggs have a lower pH, and this does not allow the shell to separate easily from the underlying albumen.
When put into vinegar the shell will disintegrate slowly
Problems when cooking eggs
If a boiled egg is overcooked, a greenish ring sometimes appears around egg yolk. This is a manifestation of the iron and sulfur compounds in the egg. It can also occur when there is an abundance of iron in the cooking water. The green ring does not affect the egg's taste; overcooking, however, harms the quality of the protein (chilling the egg for a few minutes in cold water until the egg is completely cooled prevents the greenish "ring” from forming on the surface of the yolk).[2]
Cooking also increases the risk of atherosclerosis due to increased oxidization of the cholesterol contained in the egg yolk.[3]
Egg substitutes for baking
For those who choose not to or are unable to consume eggs, alternatives used in baking include other rising agents or binding materials, such as ground flax seeds or potato flour. Tofu can also act as a partial binding agent, since it is high in lecithin due to its soy content. Applesauce can be used as well as arrowroot. Extracted soybean lecithin, in turn, is often used in packaged foods as an inexpensive substitute for egg-derived lecithin.
Egg characteristics
The shape of an egg is an oval with one end larger than the other end. The egg has cylindrical symmetry along the long axis.
An egg is surrounded by a thin, hard shell. Inside, the egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae (from the Greek word khalazi, meaning hailstone or hard lump.)
Air cell
The larger end of the egg contains the air cell that forms when the contents of the egg cool down and contract after it is laid. Chicken eggs are graded according to the size of this air cell, measured during candling. A very fresh egg has a small air cell and receives a grade of AA. As the size of the air cell increases, and the quality of the egg decreases, the grade moves from AA to A to B. This provides a way of testing the age of an egg: as the air cell increases in size, the egg becomes less dense and the larger end of the egg will rise to increasingly shallower depths when the egg is placed in a bowl of water. A very old egg will actually float in the water and should not be eaten.[4]
Shell and its colour
Egg shell color is caused by pigment deposition during egg formation in the oviduct and can vary according to breed, from the more common white or brown to pink or speckled blue-green. Although there is no significant link between shell color and nutritional value, there is often a cultural preference for one color over another. For example, in most regions of the United States, eggs are generally white; while in the northeast of that country and in the United Kingdom, eggs are generally light-brown. In Brazil, white eggs are generally regarded as industrial, and brown or reddish eggs are preferred. Regarding chicken eggs, the color of the egg depends on the breed of the bird. In general, chicken breeds with white ear lobes lay white eggs, whereas chickens with red ear lobes lay brown eggs.[5]
White (Albumen)
Yolk
The yolk in a newly laid egg is round and firm. As the yolk ages it absorbs water from the albumen which increases its size and causes it to stretch and weaken the vitelline membrane (the clear casing enclosing the yolk). The resulting effect is a flattened and enlarged yolk shape.
Yolk color is dependent on the diet of the hen; if the diet contains yellow/orange plant pigments known as xanthophylls, then they are deposited in the yolk, coloring it. A colorless diet can produce an almost colorless yolk. Farmers may enhance yolk color with artificial pigments, or with natural supplements rich in lutein (marigold petals are a popular choice), but in most locations, this activity is forbidden.
Abnormalities
Some hens will lay double-yolked eggs as the result of unsynchronized production cycles. Although heredity causes some hens to have a higher propensity to lay double-yolked eggs, these occur more frequently as occasional abnormalities in young hens beginning to lay.[citation needed] Usually a double-yolked egg will be longer and thinner than an ordinary single-yolk egg. Double-yolked eggs occur rarely, only leading to observed successful hatchings under human intervention, as the unborn chickens would otherwise fight each other and die. [6]
It is also possible for a young hen to produce an egg with no yolk at all. Yolkless eggs are usually formed about a bit of tissue that is sloughed off the ovary or oviduct. This tissue stimulates the secreting glands of the oviduct and a yolkless egg results.
Nutritional value
| Nutritional value per 100 g (3.5 oz) | |||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Energy | 647 kJ (155 kcal) | ||||||||||||||||||||||||||||||||||||||
1.12 g | |||||||||||||||||||||||||||||||||||||||
| Sugars | 1.12 g | ||||||||||||||||||||||||||||||||||||||
| Dietary fiber | 0.0 g | ||||||||||||||||||||||||||||||||||||||
10.61 g | |||||||||||||||||||||||||||||||||||||||
12.58 g | |||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||
| †Percentages estimated using US recommendations for adults,[7] except for potassium, which is estimated based on expert recommendation from the National Academies.[8] | |||||||||||||||||||||||||||||||||||||||
Eggs provide a significant amount of protein to one's diet, as well as various nutrients.
Chicken eggs are the most commonly eaten eggs, and are highly nutritious. They supply a large amount of complete, high-quality[9] protein (which contains all essential amino acids for humans), and provide significant amounts of several vitamins and minerals, including vitamin A, riboflavin, folic acid, vitamin B6, vitamin B12, choline, iron, calcium, phosphorus and potassium. They are also one of the least expensive single-food sources of complete protein. One large chicken egg contains approximately 7 grams of protein.
All of the egg's vitamin A, D and E is in the eggyolk. The egg is one of the few foods which naturally contain Vitamin D (although, since this nutrient is naturally produced in humans when their skin is exposed to sunlight, other foods' lack of natural Vitamin D is not necessarily detrimental to their nutritional value). A large egg yolk contains approximately 60 Calories (250 kilojoules); the egg white contains about 15 Calories (60 kilojoules). A large yolk contains more than two-thirds of the recommended daily intake of 300 mg of cholesterol (although one study shows that the human body does not absorb much cholesterol from eggs[10]). The yolk makes up about 33% of the liquid weight of the egg. It contains all of the fat in the egg and slightly less than half of the protein and much of the nutrients. It also contains all of the choline, and one yolk contains approximately half of the recommended daily intake. Choline is an important nutrient for development of the brain, and is said to be important for pregnant and nursing women to ensure healthy fetal brain development.[11]
Recently, chicken eggs that are especially high in Omega 3 fatty acids have come on the market. These eggs are made by feeding laying hens a diet containing polyunsaturated fats and kelp meal. Nutrition information on the packaging is different for each of the brands.
Eggs may have different nutritional content depending on the feed and living conditions of the chickens who lay them. Mother Earth News compared eggs from "battery" chickens and eggs from pastured chickens, and found that when compared to the battery eggs, the pastured eggs contained, on average, four times as many omega-3 fatty acids, twice as much vitamin E, half the cholestrol and between two and six times as much beta carotene.[12]
Health issues of eating chicken eggs
 |
Cholesterol and fat
About 60% of the calories in an egg come from fat; Chicken egg yolks contain about 10 grams of fat. People on a low-cholesterol diet may need to cut down on egg consumption, although most of the fat in egg is unsaturated fat and may not be harmful. The egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little, if any, fat.
Some people try to avoid eggs in their diet because they are high in cholesterol, which is concentrated in the yolk. This issue is sometimes addressed by eating only some or none of the yolk. People sometimes remove the yolk themselves, or may use prepared egg substitutes such as Egg Beaters.
There is debate over whether egg yolk presents a health risk. Some research suggests it may lower total Low density lipoprotein ("bad" cholesterol) while raising High density lipoprotein ("good" cholesterol).[citation needed] Some advocate the eating of raw eggs and egg yolks for this reason, as cholesterol in the yolk is healthier when uncooked. However issues of salmonella contamination remain for raw eggs. Food scientist Harold McGee argues that the cholesterol in the yolk is not what causes a problem as fat (particularly saturated) is much more likely to raise cholesterol levels than the actual consumption of cholesterol.[4]
Contamination
A health issue associated with eggs is contamination by pathogenic bacteria like Salmonella enteritidis. Contamination of eggs exiting a female bird via the cloaca may also occur with other members of the Salmonella group, so care must be taken to avoid the egg shell becoming contaminated with fecal matter. In commercial practice, eggs are quickly washed with a sanitizing solution within minutes of being laid.
Most health experts advise people to cook their eggs thoroughly before eating them, as the heat is necessary to kill any infectious micro-organisms that may be present. Raw and undercooked eggs have been associated with salmonella infection. As with meat, containers and surfaces that have been used to process raw eggs should not come in contact with ready-to-eat food.
The risk of infection from raw or undercooked eggs is dependent in part upon the sanitary conditions under which the hens are kept. Some smaller egg producers make a point of keeping their hens in cleaner (and, in some people's view, more humane) conditions, and observe few or no cases of salmonella in the birds themselves.[citation needed]
Recent evidence suggests the problem is not as prevalent as once thought. A study by the U.S. Department of Agriculture in 2002 (Risk Analysis April 2002 22(2):203-18) showed that of the 69 billion eggs produced annually, only 2.3 million of them are contaminated with salmonella - equivalent to just one in every 30,000 eggs - thus showing that salmonella infection is quite rarely induced by eggs.
Egg shells act as hermetic seals which guard against bacteria entering, but this seal can be broken through improper handling or if laid by unhealthy chickens. Most forms of contamination enter through such weaknesses in the shell. Fresher eggs often have a more prominent chalazae.
Food allergy
One of the most common food allergies in infants is eggs.[13] Infants usually have the opportunity to grow out of this allergy during childhood, if exposure is minimized. Generally, physicians will recommend feeding only the whites to infants because of the higher risk of allergic reaction to the egg yolk.
The egg allergy is prevalent enough in the United States that food labeling practices now include eggs, egg products and the processing of foods on equipment that also process foods containing eggs in a special allergen alert section of the ingredients on the labels.
Edwina Currie, salmonella, and the UK Lion mark
The Lion mark was introduced to the UK by the British Egg Information Council in 1957, later falling into disuse. British Health Minister Edwina Currie sparked a controversy in 1988 after she issued a warning about salmonella in British eggs that was criticised by the egg-producing industry for being hysterical and over-cautious, despite being substantially true. The Lion mark was revived in 1998 as a means of increasing public trust in eggs. The amount of eggs infected by salmonella was a minority and Currie resigned after the then UK Prime Minister Margaret Thatcher stated, "I had eggs for breakfast".
The Lion Quality Code of Practice includes compulsory vaccination against Salmonella enterica of all pullets destined for Lion egg-producing flocks, independent auditing improved traceability of eggs and a "best-before" date stamped on the shell and pack which shows that they are fresher than required by law, as well as on-farm and packing station hygiene controls.
The Lion Mark was itself well known in the UK from the 1950s, which was one reason why it helped to restore public confidence. The British Egg Industry also brought back the popular advertising strapline from the 1950s, Go To Work On An Egg. The British Egg Marketing Board used the "Go To Work On An Egg" strapline on a series of TV adverts starring Tony Hancock. The Egg Information Service wanted to rerun the adverts in 2007 but were blocked from doing so by the Broadcast Advertising Clearance Centre (BACC), which claimed that the adverts went against the idea of eating a balanced diet.
Chicken egg sizes
 | The examples and perspective in this article may not represent a worldwide view of the subject. |
Chicken eggs are graded by size, for the purpose of sales. The United States Department of Agriculture grades them by weight per dozen. The most common US size of chicken egg is 'Large' and is the egg size commonly referred to for recipes. The following egg masses have been calculated on the basis of the USDA grades:
| Size | Mass per egg |
|---|---|
| Jumbo | Greater than 2.5 oz. or 71g |
| Very Large or Extra Large (XL) | Greater than 2.25 oz. or 64g |
| Large (L) | Greater than 2 oz. or 57g |
| Medium (M) | Greater than 1.75 oz. or 50g |
| Small (S) | Greater than 1.5 oz. or 43g |
| Peewee | Greater than 1.25 oz. or 35g |
In the United Kingdom, modern egg sizes are defined as follows:
| Size | Mass per egg |
|---|---|
| Very Large | 73g and over |
| Large | 63-73g |
| Medium | 53-63g |
| Small | 53g and under |
In Australia, the Australian Egg Corporation defines the following sizes in its labelling guide.[14]
| Size | Mass per egg |
|---|---|
| Jumbo | 68g |
| Extra Large | 60g |
| Large | 52g |
In Western Australia, two additional sizes are also standardized by the Golden Eggs Corporation[15]
| Mega or XXXL | 72g |
|---|---|
| Medium | 43g |
In New Zealand sizes are based on the minimum mass per egg: [16]
| Size | Minimum mass per egg |
|---|---|
| 8 (Jumbo) | 68g |
| 7 (Large) | 62g |
| 6 (Standard) | 53g |
| 5 (Medium) | 44g |
| 4 (Pullet) | 35g |
| Size | Mass |
|---|---|
| Size 0 | Greater than 75g |
| Size 1 | 70g-75g |
| Size 2 | 65g-70g |
| Size 3 | 60g-65g |
| Size 4 | 55g-60g |
| Size 5 | 50g-55g |
| Size 6 | 45g-50g |
| Size 7 | less than 45g |
Issues in mass production
 | This article contains weasel words: vague phrasing that often accompanies biased or unverifiable information. |
Commercial factory farming operations often involve raising the hens in small crowded cages, preventing the chickens from engaging in natural behaviors such as wing-flapping, dust-bathing, scratching, pecking, perching and nest-building. Such restrictions can lead to frustration and cause agitated pacing and escape behavior.[17]
Many hens confined to battery cages, and some raised in cage-free conditions, are de-beaked to prevent cannibalistic pecking. According to critics of the practice, this can cause hens severe pain to the point where some may refuse to eat and prefer to starve to death. Some hens may be force molted to increase egg quality and production level after the molting.[18] Molting can be induced by extended feed withdrawal, water withdrawal or controlled lighting programs.
Laying hens are often slaughtered between 100 - 130 weeks of age when their egg productivity starts to decline.[19] Due to modern selective breeding, laying hen strains differ from meat production strains. As male birds of the laying strain do not lay eggs and are not suitable for meat production, they are generally culled at the hatchery.[20]
Free-range eggs are considered by some advocates to be an acceptable substitute to factory farmed eggs. Free range laying hens are given outdoor access instead of being contained in crowded cages. Questions on the actual living conditions of free range hens have been raised as there is no legal definition or regulations for eggs labeled as free range in the US.[21]
In the US, increased public concern for animal welfare has pushed United Egg Producers to establish a new volunteer welfare program known as United Egg Producers Certified(UEP Certified).[22] The program includes guidelines with regard to housing, feed, water, and air, space allowance, beak trimming, molting, and handling and transportation.
Culture
A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing but often by spray-painting). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl.
Egging
Although a food item, eggs are sometimes thrown at houses, cars or people. This act, known commonly as egging in the various English-speaking countries, is a minor form of vandalism and, therefore, usually a criminal offense and is capable of damaging property (egg whites can degrade certain types of vehicle paint) as well as cause serious eye injury[23]. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing. Eggs are also often thrown in protests, as they are inexpensive and nonlethal,[citation needed] yet at the same time very messy when broken. There is also an element of humiliation associated with being covered in an egg's contents, referenced by the phrase "egg on one's face."
See also
References
- ^ Evenepoel, P., Geypens, B., Luypaerts, A., Hiele, M., Ghoos, Y., & Rutgeerts, P. (1998). Digestibility of Cooked and Raw Egg Protein in Humans as Assessed by Stable Isotope Techniques. The Journal of Nutrition, 128 (10), 1716-1722. abstract
- ^ Rose Acre Farms (United Egg Producer Certified)
- ^ The role of eggs, margarines and fish oils in the nutritional management of coronary artery disease and strokes
- ^ a b McGee, H. (2004). On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner. ISBN 0-684-80001-2.
- ^ Information on chicken breeds
- ^ Double-yolked eggs and chicken development
- ^ United States Food and Drug Administration (2024). "Daily Value on the Nutrition and Supplement Facts Labels". FDA. Archived from the original on 2024-03-27. Retrieved 2024-03-28.
- ^ National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Food and Nutrition Board; Committee to Review the Dietary Reference Intakes for Sodium and Potassium (2019). Oria, Maria; Harrison, Meghan; Stallings, Virginia A. (eds.). Dietary Reference Intakes for Sodium and Potassium. The National Academies Collection: Reports funded by National Institutes of Health. Washington, DC: National Academies Press (US). ISBN 978-0-309-48834-1. PMID 30844154. Archived from the original on 2024-05-09. Retrieved 2024-06-21.
- ^ Food and Agriculture Organization article on eggs
- ^ University Science article on eggs and cholesterol
- ^ Eggs and fetal brain development
- ^ Long, Cheryl and Umut Newbury, "The Good Egg," Mother Earth News, August/September 2005
- ^ Egg Allergy Brochure, distributed by Royal Prince Alfred Hospital
- ^ Egg Labelling Guide July 2007
- ^ Golden Eggs Western Australia Product Range
- ^ [1]
- ^ Scientists and Experts on Battery Cages and Laying Hen Welfare
- ^ Eggs and force-moulting
- ^ Commercial Egg Production and Processing
- ^ Egg laying and male birds
- ^ Free-range eggs
- ^ United Egg Producers Certified Program
- ^ Stewart RM. Durnian JM. Briggs MC. "Here's egg in your eye": a prospective study of blunt ocular trauma resulting from thrown eggs. Emergency Medicine Journal. 23(10):756-8, 2006 Oct.
- Stadelman, W.J. and O.J. Cotterill. (1995). Egg Science and Technology, Fourth Edition. New York: Food Products Press.
External links
- The American Egg Board
- Nutritional values of eggs
- Nutritional value of free range eggs compared with factory eggs
- Undercover investigation of animal cruelty in Ohio's largest egg factory
- Criticism of the validity of the "Animal Care Certified" logo used by United Egg Producers(UEP)
- British Egg Industry and the Lion Mark
- 10 Health Benefits of Eggs