Egg (food)

A chicken egg (left), the most commonly eaten egg, and quail eggs (right), a delicacy

An egg is a spheroid or ovoid shaped cell laid by females of many different species, including birds, reptiles, amphibians, and fish. Eggs have been eaten by mankind for millennia. Bird eggs (including chicken and turkey eggs) consist of a protective eggshell, albumen (egg white), and vitellus (egg yolk), contained within various thin membranes.

Egg yolks and whole eggs are a good source of protein and choline.[1][2] For this reason, the USDA (United States Department of Agriculture) categorizes eggs as Meats within the Food Guide Pyramid[1]

Roe and caviar are edible eggs produced by fish.

Contents

Production

Ostrich egg (right), compared to chicken egg (lower left) and quail eggs (upper left)

Most commercially produced chicken eggs intended for human consumption are unfertilized, since the laying hens are kept without 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 for an extended amount of time (although sometimes the embryo is allowed to develop on purpose, as in balut).

Varieties

A variety of eggs as sold in Haikou, Hainan, China

Bird eggs are a common food and one of the most versatile ingredients used in cooking. They are important in many branches of the modern food industry.[3] The most commonly used bird eggs are those from the chicken. Duck and goose eggs, and smaller eggs such as quail eggs are occasionally used as a gourmet ingredient, as are the largest bird eggs, from ostriches. Gull eggs are considered a delicacy in England,[4] as well as in some Scandinavian countries, particularly in Norway. In some African countries, guineafowl eggs are commonly seen in marketplaces, especially in the spring of each year.[5] Pheasant eggs and emu eggs are perfectly edible but less widely available.[4] Sometimes they are obtainable from farmers, poulterers, or luxury grocery stores. Most wild birds’ eggs are protected by laws in many countries, which prohibit collecting or selling them, or permit these only during specific periods of the year.[4]

Quail eggs are considered a delicacy in many countries. They are used raw or cooked as tamago in sushi. In Colombia, quail eggs are considered less exotic than in other countries, and a single hard-boiled quail egg is a common topping on hot dogs and hamburgers, often fixed into place with a toothpick.

Uses

A fried chicken egg, "sunny side up".

Chicken eggs are widely used in many types of dishes, both sweet and savory, including many baked goods. Eggs can be scrambled, fried, hard-boiled, soft-boiled, pickled, and refrigerated. They can also be eaten raw, though this is not recommended for people who may be especially susceptible to salmonella, such as the elderly, the infirm, or pregnant women. In addition, the protein in raw eggs is only 51% bio-available, whereas that of 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.[6] As an ingredient, egg yolks are an important emulsifier in the kitchen, and the proteins in egg white allow it to form foams and aerated dishes.

Soft-boiled quail eggs, with potato galettes

The albumen, or egg white, contains protein but little or no fat, and can be used in cooking separately from the yolk. Egg whites may be aerated or whipped to a light, fluffy consistency and are often used in desserts such as meringues and mousse. Ground egg shells are sometimes used as a food additive to deliver calcium.[7]

Every part of an egg is edible, although the eggshell is generally discarded.

Flavor

Although the age of the egg and the conditions of its storage have a greater influence, the bird's diet does affect the flavor of the egg.[8] For example, when a brown-egg chicken breed eats rapeseed or soy meals, its intestinal microbes metabolize them into fishy-smelling triethylamine, which ends up in the egg.[8] The unpredictable diet of free-range hens will produce unpredictable eggs.[8]

Cooking

Shopping for chicken eggs in a grocery store.

Egg white coagulates, or solidifies, when it reaches temperatures between 144 °F and 149 °F (62.2 °C-65 °C).[9] Egg yolk coagulates at slightly higher temperatures, between 149 °F and 158 °F (65 °C-70 °C).[9]

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).

Cooking also increases the risk of atherosclerosis due to increased oxidization of the cholesterol contained in the egg yolk.[10]

Preservation

Salted duck egg

Preservation of edible eggs is extremely important, as an improperly handled egg can contain elevated levels of Salmonella, bacteria that can cause severe food poisoning. The simplest method to preserve an egg is to treat it with salt. Salt draws water out of bacteria and molds, which prevents their growth.[11] The Chinese salted duck egg is made by immersing duck eggs in brine, or coating them individually with a paste of salt and mud or clay. The eggs stop absorbing salt after about a month, having reached chemical equilibrium.[11] Their yolks take on an orange-red color and solidify, but the white remains liquid. They are boiled before consumption and often served with rice congee.

Pickled egg, colored with beetroot juice

Another method is to make pickled eggs, by boiling them first and immersing them in a mixture of vinegar, salt, and spices like ginger or allspice. Frequently, beetroot juice is added to impart a red color to the eggs.[12] If the eggs are immersed in it for a few hours, the distinct red, white, and yellow colors can be seen when the eggs are sliced.[12] If marinated for several days or more, the red color will reach the yolk.[12] If the eggs are marinated in the mixture for several weeks or more, the vinegar will dissolve much of the shell's calcium carbonate and penetrate the egg, making it acidic enough to inhibit the growth of bacteria and molds.[11] Pickled eggs made this way will generally keep for a year or more without refrigeration.[11]

Century egg

A century egg or hundred-year-old egg is preserved by coating an egg in a mixture of clay, wood ash, salt, lime, and rice straw for several weeks to several months, depending on the method of processing. After the process is completed, the yolk becomes a dark green, cream-like substance with a strong odor of sulfur and ammonia, while the white becomes a dark brown, transparent jelly with a comparatively mild, distinct flavor. The transforming agent in a century egg is its alkaline material, which gradually raises the pH of the egg from around 9 to 12 or more.[13] This chemical process breaks down some of the complex, flavorless proteins and fats of the yolk into simpler, flavorful ones, which in some way may be thought of as an "inorganic version" of fermentation.

Substitutes

For those who do not consume eggs, alternatives used in baking include other rising agents or binding materials, such as ground flax seeds or potato starch 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 and banana. Extracted soybean lecithin, in turn, is often used in packaged foods as an inexpensive substitute for egg-derived lecithin.

Other egg substitutes are made from just the white of the egg for those who worry about the high cholesterol and fat content in eggs. These products usually have added vitamins and minerals as well as vegetable-based emulsifiers and thickeners such as xanthan gum or guar gum. These allow the product to maintain the nutrition and several culinary properties of real eggs, making possible foods like Hollandaise sauce, custard, mayonnaise, and most baked goods with these substitutes.

History

Bird eggs have been valuable foodstuff since prehistory, in both hunting societies and more recent cultures where birds were domesticated. The chicken was probably domesticated for its eggs from jungle fowl native to tropical and subtropical Southeast Asia and India before 7500 BCE. Chickens were brought to Sumer and Egypt by 1500 BCE, and arrived in Greece around 800 BCE, where the quail had been the primary source of eggs.[14] In Thebes, Egypt, the tomb of Haremhab, built about 1420 BCE, shows a depiction of a man carrying bowls of ostrich eggs and other large eggs, presumably those of the pelican, as offerings.[15] In ancient Rome, eggs were preserved using a number of methods, and meals often started with an egg course.[15] The Romans crushed the shell in their plate to prevent evil spirits from hiding there.[3] In the Middle Ages, eggs were forbidden during Lent because of their richness.[3] It is possible that the word mayonnaise was derived from moyeu, the medieval French word for the yolk meaning center or hub.[3]

Egg scrambled with acidic fruit juices were popular in France in the 17th century; this may have been the origin of lemon curd.[8]

The dried egg industry developed in the 19th century, before the rise of the frozen egg industry.[16] In 1878, a company in St. Louis, Missouri started to transform egg yolk and white into a light-brown, meal-like substance by using a drying process.[16] The production of dried eggs significantly expanded during World War II, for use by the United States Armed Forces and its allies.[16]

The egg carton was invented by Joseph Coyle in Smithers, British Columbia, to solve a dispute about broken eggs between a farmer in Bulkley Valley and the owner of the Aldermere Hotel. Early egg cartons were made of paper.[17]

Anatomy and characteristics

See also: Egg (biology)
Schematic of a chicken egg:
1. Eggshell
2. Outer membrane
3. Inner membrane
4. Chalaza
5. Exterior albumen
6. Middle albumen
7. Vitelline membrane
8. Nucleus of pander
9. Germinal disc (nucleus)
10. Yellow yolk
11. White yolk
12. Internal albumen
13. Chalaza
14. Air cell
15. Cuticula

The shape of an egg is an ovate spheroid 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.[14]

Shell

Egg shell color is caused by pigment deposition during egg formation in the oviduct and can vary according to species and breed, from the more common white or brown to pink or speckled blue-green. In general, chicken breeds with white ear lobes lay white eggs, whereas chickens with red ear lobes lay brown eggs.[18] 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, chicken eggs are generally white; while in the northeast of that country, and in countries as diverse as Costa Rica, Ireland, and the United Kingdom, they are generally light-brown. In Brazil and Poland, white chicken eggs are generally regarded as industrial, and brown or reddish ones are preferred.

White (albumen)

Yolk

Main article: Egg 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. Lutein is the most abundant pigment in egg yolk.[19] A colorless diet can produce an almost colorless yolk. Yolk color is for example enhanced if the diet includes products such as yellow corn and marigold petals.[20] In the US, the use of artificial color additives is forbidden.[20]

Abnormalities

See Egg yolk#Double-yolk eggs and Egg yolk#Yolkless eggs.

Nutritional value

Chicken egg, whole, hard-boiled
Nutritional value per 100 g (3.5 oz)
Energy 647 kJ (155 kcal)
Carbohydrates 1.12 g
Fat 10.6 g
Protein 12.6 g
Tryptophan 0.153 g
Threonine 0.604 g
Isoleucine 0.686 g
Leucine 1.075 g
Lysine 0.904 g
Methionine 0.392 g
Cystine 0.292 g
Phenylalanine 0.668 g
Tyrosine 0.513 g
Valine 0.767 g
Arginine 0.755 g
Histidine 0.298 g
Alanine 0.700 g
Aspartic acid 1.264 g
Glutamic acid 1.644 g
Glycine 0.423 g
Proline 0.501 g
Serine 0.936 g
Water 75 g
Vitamin A equiv. 140 μg (16%)
Thiamine (Vit. B1) 0.066 mg (5%)
Riboflavin (Vit. B2) 0.5 mg (33%)
Pantothenic acid (B5) 1.4 mg (28%)
Folate (Vit. B9) 44 μg (11%)
Calcium 50 mg (5%)
Iron 1.2 mg (10%)
Magnesium 10 mg (3%)
Phosphorus 172 mg (25%)
Potassium 126 mg (3%)
Zinc 1.0 mg (10%)
Choline 225 mg
Cholesterol 424 mg
For edible portion only. Refuse: 12% (Shell). One large egg is 50 grams.
Percentages are relative to US recommendations for adults.
Source: USDA Nutrient database

Eggs add protein to one's diet, as well as various other nutrients.

Chicken eggs are the most commonly eaten eggs. They supply all essential amino acids for humans,[21] and provide several vitamins and minerals, including vitamin A, riboflavin (vitamin B2), folic acid (vitamin B9), vitamin B6, vitamin B12, choline, iron, calcium, phosphorus and potassium. They are also an inexpensive single-food source of protein.

All of the egg's vitamin A, D and E are in the egg yolk. The egg is one of the few foods that naturally contains vitamin D. 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 indicates that the human body may not absorb much cholesterol from eggs[22]). The yolk makes up about 33% of the liquid weight of the egg. It contains all of the fat, slightly less than half of the protein, and most of the other 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.[23]

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.

Cooked eggs are easier to digest,[24] as well as having a lower risk of salmonellosis.[25]

Health issues

Cholesterol and fat

More than half the calories found in eggs come from the fat in the yolk; a large 50-gram chicken egg contains approximately 5 grams of fat. People on a low-cholesterol diet may need to reduce egg consumption; however, only 27% of the fat in egg is saturated fat (palmitic, stearic and myristic acids[26]) that contains LDL cholesterol. The egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little, if any, fat.

There is debate over whether egg yolk presents a health risk. Some research suggests dietary cholesterol increases the ratio of total to HDL cholesterol and, therefore, adversely affects the body's cholesterol profile;[27] whereas other studies show that moderate consumption of eggs, up to one a day, does not appear to increase heart disease risk in healthy individuals.[28] Harold McGee argues that the cholesterol in the yolk is not what causes a problem, because fat (particularly saturated) is much more likely to raise cholesterol levels than the actual consumption of cholesterol.[14] A 2007 study of nearly 10,000 adults demonstrated no correlation between moderate (6 per week) egg consumption and cardiovascular disease or strokes except in the sub-population of diabetic patients which presented an increased risk of coronary heart disease.[29] Other research supports the idea that a high egg intake increases cardiovascular risk in diabetic patients.[30]

Type 2 diabetes

Consumption of eggs has been linked to an increased risk of type 2 diabetes in both men and women. A 2008 study using data on over 50,000 individuals collected by the Physicians' Health Study I (1982-2007) and the Women's Health Study (1992-2007) determined that the “data suggest that high levels of egg consumption (daily) are associated with an increased risk of type 2 diabetes.”[31]

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 genus, 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. The risk of infection from raw or undercooked eggs is dependent in part upon the sanitary conditions under which the hens are kept.

Health experts advise people to refrigerate eggs, use them within two weeks, cook them thoroughly, and never consume raw eggs.[25] As with meat, containers and surfaces that have been used to process raw eggs should not come in contact with ready-to-eat food.

A study by the U.S. Department of Agriculture in 2002 (Risk Analysis April 2002 22(2):203-18) suggests the problem is not as prevalent as once thought. It showed that of the 69 billion eggs produced annually, only 2.3 million are contaminated with Salmonella—equivalent to just one in every 30,000 eggs—thus showing that Salmonella infection is quite rarely induced by eggs. However, this has not been the case in other countries where Salmonella enteritidis and Salmonella typhimurium infections due to egg consumptions are major concerns.[32][33][34] 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. In the UK, the British Egg Industry Council award the lions stamp to eggs that, among other things, come from hens that have been vaccinated against Salmonella. [35][36][37]

Food allergy

One of the most common food allergies in infants is eggs.[38] Infants usually have the opportunity to grow out of this allergy during childhood, if exposure is minimized.[39] Allergic reactions against egg white are more common than reactions against egg yolks.[40]

In addition to true allergic reactions, some people experience a food intolerance to egg whites.[40]

Food labeling practices in most developed countries 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.

Antibiotic resistance

Information obtained by the Canadian Integrated Program for Antimicrobial Resistance (CIPARS) “strongly indicates that cephalosporin resistance in humans is moving in lockstep with use of the drug in poultry production.” According to the Canadian Medical Association Journal, the unapproved antibiotic ceftiofur is routinely injected into eggs in Quebec and Ontario to discourage infection of hatchlings. Although the data are contested by the industry, antibiotic resistance in humans appears to be directly related to the antibiotic's use in eggs.[41]

Chicken egg grading

The US Department of Agriculture grade eggs by the interior quality of the egg (see Haugh unit) and the appearance and condition of the egg shell. Eggs of any quality grade may differ in weight (size).

In other countries, particularly in European Union, eggs are graded by the hen farming method instead, e.g. from free range hens, battery cages, etc.

Chicken egg sizes

Medium white eggs in carton

Chicken eggs are graded by size, for the purpose of sales. The United States Department of Agriculture sizing is based 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 sizing:

Modern Sizes (USA)
Size Mass per egg Cooking Yield (Volume)[3]
Jumbo Greater than 2.5 oz. or 71 g
Very Large or Extra-Large (XL) Greater than 2.25 oz. or 64 g 56 mL (4 tbsp)
Large (L) Greater than 2 oz. or 57 g 46 mL (3.25 tbsp)
Medium (M) Greater than 1.75 oz. or 50 g 43 mL (3 tbsp)
Small (S) Greater than 1.5 oz. or 43 g
Peewee Greater than 1.25 oz. or 35 g

In Canada, modern egg sizes are defined as follows:

Modern Sizes (Canada)[42]
Size Mass per egg
Jumbo 70 g or more
Extra Large 63-69 g
Large 56-62 g
Medium 49-55 g
Small 42-48 g
Peewee Less than 41 g

In Europe, modern egg sizes are defined as follows:

Modern Sizes (Europe)
Size Mass per egg
Very Large 73 g and over
Large 63-73 g
Medium 53-63 g
Small 53 g and under

In Australia, the Australian Egg Corporation defines the following sizes in its labeling guide.[43]

Modern Sizes (Australia)
Size Mass per egg
Jumbo 68 g
Extra-Large 60 g
Large 52 g

In Western Australia, two additional sizes are also standardized by the Golden Eggs Corporation[44]

Additional Sizes (Western Australia)
Mega or XXXL 72 g
Medium 43 g

In New Zealand sizes are based on the minimum mass per egg:[45]

Modern Sizes (New Zealand)
Size Minimum mass per egg
8 (Jumbo) 68 g
7 (Large) 62 g
6 (Standard) 53 g
5 (Medium) 44 g
4 (Pullet) 35 g
Traditional Sizes
Size Mass
Size 0 Greater than 75g
Size 1 70 g - 75 g
Size 2 65 g - 70 g
Size 3 60 g - 65 g
Size 4 55 g - 60 g
Size 5 50 g - 55 g
Size 6 45 g - 50 g
Size 7 less than 45 g

Issues in mass production

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 pacing and escape behavior.[46]

Many hens confined to battery cages, and some raised in cage-free conditions, are de-beaked to prevent harming each other and cannibalism. According to critics of the practice, this can cause hens severe pain to the point where some may refuse to eat and starve to death. Some hens may be force molted to increase egg quality and production level after the molting.[47] 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.[48] 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.[49]

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.[50]

In the US, increased public concern for animal welfare has pushed various egg producers to release eggs under a variety of different standards. The most widespread standard in use is used by United Egg Producers and is a volunteer program known as United Egg Producers Certified (UEP Certified).[51] The program includes guidelines with regard to housing, feed, water, air, space allowance, beak trimming, molting, handling, and transportation; however, critics such as The Humane Society have alleged UEP Certification misleadingly allows for a significant amount of animal cruelty.[52] Other standards include "Cage Free", "Natural", "Certified Humane", and "Certified Organic." Of these standards, "Certified Humane", which carries requirements for stocking density and cage-free keeping, among others, and "Certified Organic", which requires hens have outdoor access and are fed only organic, vegetarian feed, among other requirements, are the most stringent.[53][54]

The European Union will introduce an EU-wide ban on the use of conventional battery cages for egg-laying hens. This ban is expected to come into effect from 1 January 2012, as per EU Directive 1999/74/EC.[55] The EU will instead permit the use of "enriched" cages that must meet certain space and amenity requirements. Egg producers in many member states have objected to the ban.

Cultural significance

Further information: Egg decorating, Easter egg, and Egging
Hanácké kraslice, Easter eggs from the Haná region, the Czech Republic

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.

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 causing serious eye injury.[56] 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, yet very messy when broken.

References

  1. ↑ 1.0 1.1 Agricultural Marketing Service. "How to Buy Eggs". Home and Garden Bulletin (United States Department of Agriculture (USDA)) (264): 1 
  2. ↑ Howe, Juliette C.; Williams, Juhi R.; Holden, Joanne M. (March 2004). USDA Database for the Choline Content of Common Foods. United States Department of Agriculture (USDA). p. 10. http://www.nal.usda.gov/fnic/foodcomp/Data/Choline/Choline.pdf 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Montagne, Prosper (2001). Larousse Gastronomique. Clarkson Potter. pp. 447–448. ISBN 0609609718. 
  4. ↑ 4.0 4.1 4.2 Roux, Michel; Martin Brigdale (2006). Eggs. Wiley. p. 8. ISBN 0471769134. 
  5. ↑ Stadelman, William (1995). Egg Science and Technology. Haworth Press. p. 1. ISBN 1560228547. 
  6. ↑ 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
  7. ↑ Anne Schaafsma, Gerard M Beelen (1999). "Eggshell powder, a comparable or better source of calcium than purified calcium carbonate: piglet studies". Journal of the Science of Food and Agriculture 79 (12): 1596–1600. doi:10.1002/(SICI)1097-0010(199909)79:12<1596::AID-JSFA406>3.0.CO;2-A. http://www3.interscience.wiley.com/cgi-bin/abstract/63003036/ABSTRACT. 
  8. ↑ 8.0 8.1 8.2 8.3 McGee, Harold (2004). On Food and Cooking: The Science and Lore of the Kitchen. Scribner. p. 87. ISBN 0-684-80001-2. 
  9. ↑ 9.0 9.1 "Frequently Asked Questions About Egg Food Safety". Egg Safety Center, Alpharetta, GA. http://www.eggsafety.org/f_a_q.htm. 
  10. ↑ USA (2009-10-16). "The role of eggs, margarines and fish oils in the nutritional management of coronary artery disease and strokes". Ncbi.nlm.nih.gov. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=retrieve&dopt=citation&list_uids=15477726. Retrieved 2010-01-10. 
  11. ↑ 11.0 11.1 11.2 11.3 McGee, Harold (2004). On Food and Cooking: The Science and Lore of the Kitchen. Scribner. p. 116. ISBN 0-684-80001-2. 
  12. ↑ 12.0 12.1 12.2 Stadelman, William (1995). Egg Science and Technology. Haworth Press. pp. 479–480. ISBN 1560228547. 
  13. ↑ McGee, Harold (2004). On Food and Cooking: The Science and Lore of the Kitchen. Scribner. p. 117. ISBN 0-684-80001-2. 
  14. ↑ 14.0 14.1 14.2 McGee, Harold (2004). McGee on Food and Cooking. Hodder and Stoughton. p. 70. ISBN 0340831499. 
  15. ↑ 15.0 15.1 Brothwell, Don R.; Patricia Brothwell (1997). Food in Antiquity: A Survey of the Diet of Early Peoples. Johns Hopkins University Press. pp. 54–55. ISBN 0801857406. 
  16. ↑ 16.0 16.1 16.2 Stadelman, William (1995). Egg Science and Technology. Haworth Press. pp. 221–223. ISBN 1560228547. 
  17. ↑ Easterday, Jim (April 21, 2005). "The Coyle Egg-Safety Carton". Hiway16 Magazine. http://www.bcnorth.ca/magazine/pages/Jim/egg/egg1.htm. Retrieved 2008-04-21. 
  18. ↑ "Information on chicken breeds" (PDF). http://www.ces.purdue.edu/extmedia/AS/AS-518.pdf. Retrieved 2010-01-10. 
  19. ↑ F. Karadas et al., Effects of carotenoids from lucerne, marigold and tomato on egg yolk pigmentation and carotenoid composition. Br Poult Sci. 2006 Oct;47(5):561-6. PMID 17050099 (PubMed)
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  20. ↑ 20.0 20.1 Shell eggs from farm to table. USDA Food Safety and Inspection Service (2008).
  21. ↑ "Food and Agriculture Organization article on eggs". Fao.org. http://www.fao.org/AG/againfo/subjects/en/eggs.html. Retrieved 2010-01-10. 
  22. ↑ "University Science article on eggs and cholesterol". Unisci.com. 2001-10-29. http://unisci.com/stories/20014/1029013.htm. Retrieved 2010-01-10. 
  23. ↑ "Eggs and fetal brain development". Pdrhealth.com. http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/cho_0283.shtml. Retrieved 2010-01-10. 
  24. ↑ Evenepoel, P; Geypens B, Luypaerts A et al. (October 1998). "Digestibility of cooked and raw egg protein in humans as assessed by stable isotope techniques". The Journal of Nutrition 128 (10): 1716–1722. PMID 9772141. http://jn.nutrition.org/cgi/content/full/128/10/1716. 
  25. ↑ 25.0 25.1 "Eggs -- No Yolking Matter." Nutrition Action Health Letter, July/August 1997.
  26. ↑ U.S. Department of Agriculture, Agricultural Research Service. 2007. USDA National Nutrient Database for Standard Reference, Release 20. Nutrient Data Laboratory Home Page
  27. ↑ Weggemans RM, Zock PL, Katan MB (2001). "Dietary cholesterol from eggs increases the ratio of total cholesterol to high-density lipoprotein cholesterol in humans: a meta-analysis". Am. J. Clin. Nutr. 73 (5): 885–91. PMID 11333841. 
  28. ↑ Hu FB, Stampfer MJ, Rimm EB, et al. (1999). "A prospective study of egg consumption and risk of cardiovascular disease in men and women". JAMA 281 (15): 1387–94. doi:10.1001/jama.281.15.1387. PMID 10217054. 
  29. ↑ Qureshi AI, Suri FK, Ahmed S, Nasar A, Divani AA, Kirmani JF (2007). "Regular egg consumption does not increase the risk of stroke and cardiovascular diseases". Med. Sci. Monit. 13 (1): CR1–8. PMID 17179903. 
  30. ↑ Schärer M, Schulthess G (2005). "[Egg intake and cardiovascular risk]" (in German). Ther Umsch 62 (9): 611–3. PMID 16218496. 
  31. ↑ "Egg Consumption and Risk of Type 2 Diabetes in Men and Women". Biowizard.com. http://www.biowizard.com/pmabstract.php?pmid=19017774. Retrieved 2010-01-10. 
  32. ↑ Kimura, Akiko C. et al.; Reddy, V; Marcus, R; Cieslak, PR; Mohle-Boetani, JC; Kassenborg, HD; Segler, SD; Hardnett, FP et al. (2004). "Chicken Consumption Is a Newly Identified Risk Factor for Sporadic Salmonella enterica Serotype Enteritidis Infections in the United States: A Case-Control Study in FoodNet Sites". Clinical Infectious Diseases 38: S244–S252. doi:10.1086/381576. PMID 15095196. 
  33. ↑ Little, C.L et al.; Surman-Lee, S; Greenwood, M; Bolton, FJ; Elson, R; Mitchell, RT; Nichols, GN; Sagoo, SK et al. (2007). "Public health investigations of Salmonella Enteritidis in catering raw shell eggs, 2002-2004". Letters in Applied Microbiology (Blackwell Publishing) 44 (6): 595–601. doi:10.1111/j.1472-765X.2007.02131.x. PMID 17576219. 
  34. ↑ Stephens, N. et al.; Sault, C; Firestone, SM; Lightfoot, D; Bell, C (2007). "Large outbreaks of Salmonella Typhimurium phage type 135 infections associated with the consumption of products containing raw egg in Tasmania". Communicable diseases intelligence (Blackwell Publishing) 31 (1): 118–24. PMID 17503652. 
  35. ↑ Knowledge Guide, British Egg Information Service. Retrieved 26 February 2010.
  36. ↑ Lion Code of Practice. Retrieved 26 February 2010.
  37. ↑ Farming UK news article. Retrieved 26 February 2010.
  38. ↑ Egg Allergy Brochure, distributed by Royal Prince Alfred Hospital
  39. ↑ “Egg Allergy Facts” Asthma and Allergy Foundation of America
  40. ↑ 40.0 40.1 Arnaldo Cantani (2008). Pediatric Allergy, Asthma and Immunology. Berlin: Springer. pp. 710–713. ISBN 3-540-20768-6. 
  41. ↑ Gulli, Cathy (June 17, 2009). "Playing chicken with antibiotics Antibiotics injected into chicken eggs is making Canadians resistant to meds". Macleans Magazine. http://www2.macleans.ca/2009/06/17/playing-chicken-with-antibiotics/. Retrieved 2009-06-24. 
  42. ↑ Source: Agriculture and Agri-food Canada
  43. ↑ Egg Labelling Guide July 2007
  44. ↑ "Golden Eggs Western Australia Product Range". Goldeneggs.com.au. http://www.goldeneggs.com.au/product_range/golden_eggs.html. Retrieved 2010-01-10. 
  45. ↑ "Egg Quality". Egg Producers Federation of New Zealand. http://www.eggfarmers.org.nz/egg-quality.asp. Retrieved 2010-01-10. 
  46. ↑ "Scientists and Experts on Battery Cages and Laying Hen Welfare". Hsus.org. http://www.hsus.org/farm/resources/research/welfare/scientists_and_experts_on_battery_cages.html. Retrieved 2010-01-10. 
  47. ↑ "Eggs and force-moulting". Ianrpubs.unl.edu. http://ianrpubs.unl.edu/poultry/mp70/mp70-15.htm. Retrieved 2010-01-10. 
  48. ↑ "Commercial Egg Production and Processing". Ag.ansc.purdue.edu. http://ag.ansc.purdue.edu/poultry/publication/commegg/. Retrieved 2010-01-10. 
  49. ↑ "Egg laying and male birds". Vegsoc.org. http://www.vegsoc.org/info/laying.html#male. Retrieved 2010-01-10. 
  50. ↑ "Free-range eggs". Cok.net. http://www.cok.net/lit/freerange.php. Retrieved 2010-01-10. 
  51. ↑ United Egg Producers Certified Program
  52. ↑ "Wondering What The "UEP Certified" Logo Means?". Hsus.org. http://www.hsus.org/farm/resources/pubs/uep_certified_logo.html. Retrieved 2010-01-10. 
  53. ↑ "Egg Labels". EggIndustry.com. http://www.eggindustry.com/cfi/faq/. Retrieved 2010-01-10. 
  54. ↑ The Humane Society of the United States. "A Brief Guide to Egg Carton Labels and Their Relevance to Animal Welfare". Hsus.org. http://www.hsus.org/farm/resources/pubs/animal_welfare_claims_on_egg_cartons.html. Retrieved 2010-01-10. 
  55. ↑ "EUR-Lex - 31999L0074 - EN". Eur-lex.europa.eu. http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31999L0074:EN:HTML. Retrieved 2010-01-10. 
  56. ↑ 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.

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