Eggs as food
Humans and their hominid relatives have consumed eggs for millions of years.
Hens and other egg-laying creatures are raised throughout the world, and
History
Bird eggs have been valuable foodstuffs since prehistory, in both hunting societies and more recent cultures where birds were domesticated. The chicken was most likely domesticated for its eggs (from jungle fowl native to tropical and subtropical Southeast Asia and Indian subcontinent) 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.[4] In Thebes, Egypt, the tomb of Haremhab, dating to approximately 1420 BCE, shows a depiction of a man carrying bowls of ostrich eggs and other large eggs, presumably those of the pelican, as offerings.[5] In ancient Rome, eggs were preserved using a number of methods and meals often started with an egg course.[5] The Romans crushed the shells in their plates to prevent evil spirits from hiding there.[6]
In the Middle Ages, eggs were forbidden during Lent because of their richness,[6] although the motivation for forgoing eggs during Lent was not entirely religious. An annual pause in egg consumption allowed farmers to rest their flocks, and also to limit their hens' consumption of feed during a time of year when food stocks were usually scarce.
Eggs scrambled with acidic fruit juices were popular in
The dried egg industry developed in the nineteenth century, before the rise of the frozen egg industry.
In 1911, the
Whereas the wild Asian fowl from which domesticated chickens are descended typically lay about a dozen eggs each year during the breeding season, several millennia of selective breeding have produced domesticated hens capable of laying more than three hundred eggs each annually, and to lay eggs year round.
Varieties
The most commonly used bird eggs are those from the
The largest bird eggs, from ostriches, tend to be used only as special luxury food. Gull eggs are considered a delicacy in England,[11] as well as in some Scandinavian countries, particularly in Norway. In some African countries, guineafowl eggs often are seen in marketplaces, especially in the spring of each year.[12] Pheasant eggs and emu eggs are edible, but less widely available;[11] sometimes they are obtainable from farmers, poulterers, or luxury grocery stores. In many countries, wild bird eggs are protected by laws which prohibit the collecting or selling of them, or permit collection only during specific periods of the year.[11]
Production
In 2017, world production of chicken eggs was 80.1 million tonnes. The largest producers were China with 31.3 million of this total, the United States with 6.3 million, India at 4.8 million, Mexico at 2.8 million, Japan at 2.6 million, and Brazil and Russia with 2.5 million each.[13] The largest egg factory in British Columbia, for example, ships 12 million eggs per week.[14]
For the month of January 2019, the United States produced 9.41 billion eggs, with 8.2 billion for table consumption and 1.2 billion for raising chicks.[15] Americans are projected to each consume 279 eggs in 2019, the highest since 1973, but less than the 405 eggs eaten per person in 1945.[15]
During production, eggs can be
Anatomy and characteristics
Bird and reptile eggs consist of a protective
Air cell
The larger end of the egg contains an 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 due to air being drawn through pores in the shell as water is lost, 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 float in the water and should not be eaten,[17] especially if a foul odor can be detected if the egg is cracked open.[18]
Shell
Eggshell color is caused by pigment deposition during egg formation in the oviduct and may vary according to species and breed, from the more common white or brown to pink or speckled blue-green. Generally, chicken breeds with white ear lobes lay white eggs, whereas chickens with red ear lobes lay brown eggs.[19] Although there is no significant link between shell color and nutritional value, often there is a cultural preference for one color over another (see § Color of eggshell below). As candeling is less effective with brown eggs, they have a significantly higher incidence of blood spots.[20]
Membrane
The
These membranes may be used commercially as a dietary supplement.White
"White" is the common name for the clear liquid (also called the albumen or the glair/glaire) contained within an egg. Colorless and transparent initially, upon cooking it turns white and opaque. In chickens, it is formed from the layers of secretions of the anterior section of the hen oviduct during the passage of the egg.[22] It forms around both fertilized and unfertilized yolks. The primary natural purpose of egg white is to protect the yolk and provide additional nutrition during the growth of the embryo.
Egg white consists primarily of approximately 90 percent water into which is dissolved 10 percent proteins (including albumins, mucoproteins, and globulins). Unlike the yolk, which is high in lipids (fats), egg white contains almost no fat and the carbohydrate content is less than one percent. Egg white has many uses in food and many other applications, including the preparation of vaccines, such as those for influenza.[23]
Yolk
Yolk color is dependent on the diet of the hen. If the diet contains yellow or orange plant
Abnormalities
Abnormalities that have been found in eggs purchased for human consumption include:
- Double-yolk eggs, when an egg contains two or more yolks, occurs when ovulation occurs too rapidly, or when one yolk becomes joined with another yolk.[26]
- Yolkless eggs, which contain whites but no yolk, usually occurs during a pullet's first effort, produced before her laying mechanism is fully ready.[27]
- Double-shelled eggs, where an egg may have two or more outer shells, is caused by a counter-peristalsis contraction and occurs when a second oocyte is released by the ovary before the first egg has completely traveled through the oviduct and been laid.[28]
- Shell-less or thin-shelled eggs may be caused by egg drop syndrome.[29]
Culinary properties
Types of dishes
Chicken eggs are widely used in many types of dishes, both sweet and savory, including many
As a cooking ingredient, egg yolks are an important
The
Ground eggshells sometimes are used as a food additive to deliver calcium.[31] Every part of an egg is edible, although the eggshell is generally discarded. Some recipes call for immature or unlaid eggs, which are harvested after the hen is slaughtered or cooked, while still inside the chicken.[32]
Cooking
Eggs contain multiple proteins that gel at different temperatures within the yolk and the white, and the temperature determines the gelling time. Egg yolk becomes a gel, or solidifies, between 61 and 70 °C (142 and 158 °F). Egg white gels at different temperatures: 60 to 73 °C (140 to 163 °F). The white contains exterior albumen which sets at the highest temperature. In practice, in many cooking processes the white gels first because it is exposed to higher temperatures for longer.[33]
Salmonella is killed instantly at 71 °C (160 °F), but also is killed from 54.5 °C (130.1 °F), if held at that temperature for sufficiently long time periods. To avoid the issue of salmonella, eggs may be pasteurized in-shell at 57 °C (135 °F) for an hour and 15 minutes. Although the white then is slightly milkier, the eggs may be used in normal ways. Whipping for meringue takes significantly longer, but the final volume is virtually the same.[34]
If a boiled egg is overcooked, a greenish ring sometimes appears around the egg yolk due to changes to the iron and sulfur compounds in the egg.[35] It also may occur with an abundance of iron in the cooking water.[36] Overcooking harms the quality of the protein.[37] Chilling an overcooked egg for a few minutes in cold water until it is completely cooled may prevent the greenish ring from forming on the surface of the yolk.[38]
Peeling a cooked egg is easiest when the egg was put into boiling water as opposed to slowly heating the egg from a start in cold water.[39]
Flavor variations
Although the age of the egg and the conditions of its storage have a greater influence, the bird's diet affects the flavor of the egg.[7] For example, when a brown-egg chicken breed eats rapeseed (canola) or soy meals, its intestinal microbes metabolize them into fishy-smelling triethylamine, which ends up in the egg.[7] The unpredictable diet of free-range hens will produce likewise, unpredictable egg flavors.[7] Duck eggs tend to have a flavor distinct from, but still resembling, chicken eggs.
Eggs may be soaked in mixtures to absorb flavor. Tea eggs, a common snack sold from street-side carts in China, are steeped in a brew from a mixture of various spices, soy sauce, and black tea leaves to give flavor.
Storage
Careful storage of edible eggs is extremely important, as an improperly handled egg may contain elevated levels of
Refrigeration also preserves the taste and texture, however, intact eggs (unwashed and unbroken) may be left unrefrigerated for several months without spoiling.[42] In Europe, eggs are not usually washed, and the shells are dirtier, however the cuticle is undamaged, and they do not require refrigeration.[41] In the UK in particular, hens are immunized against salmonella and generally, their eggs are safe for 21 days.[41]
Preservation
The simplest method to preserve an egg is to treat it with
Another method is to make
A
Nutrition and health effects
Nutritional value per 100 g (3.5 oz) | |
---|---|
Energy | 647 kJ (155 kcal) |
1.12 g | |
10.6 g | |
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 |
Niacin (B3) | 0% 0.064 mg |
Pantothenic acid (B5) | 28% 1.4 mg |
Vitamin B6 | 7% 0.121 mg |
Folate (B9) | 11% 44 μg |
Vitamin B12 | 46% 1.11 μg |
Choline | 53% 294 mg |
Vitamin D | 11% 87 IU |
Vitamin E | 7% 1.03 mg |
Vitamin K | 0% 0.3 μg |
Minerals | Quantity %DV† |
Calcium | 4% 50 mg |
Iron | 7% 1.2 mg |
Magnesium | 2% 10 mg |
Phosphorus | 14% 172 mg |
Potassium | 4% 126 mg |
Sodium | 5% 126 mg |
Zinc | 9% 1.0 mg |
Other constituents | Quantity |
Water | 75 g |
Cholesterol | 373 mg |
For edible portion only. Refuse: 12% (shell). An egg just large enough to be classified as "large" in the U.S. yields 50 grams of egg without shell. This size egg is classified as "medium" in Europe and "standard" in New Zealand. Link to USDA Database entry | |
†Percentages estimated using US recommendations for adults,[46] except for potassium, which is estimated based on expert recommendation from the National Academies.[47] |
Egg yolks and whole eggs store significant amounts of
A 50-gram (1.8 oz) medium/large chicken egg provides approximately 70 kilocalories (290 kJ) of food energy and 6 grams of protein.[50][51]
Eggs (boiled) supply several vitamins and minerals as significant amounts of the
The diet of laying hens also may affect the nutritional quality of eggs. For instance, chicken eggs that are especially high in
A 2010 USDA study determined there were no significant differences of
Cooked eggs are easier to digest than raw eggs,[56] as well as having a lower risk of salmonellosis.[57]
Cholesterol and fat
More than half the calories found in eggs come from the fat in the yolk; 50 grams of chicken egg (the contents of an egg just large enough to be classified as "large" in the US, but "medium" in Europe) contains approximately five grams of fat. Saturated fat (palmitic, stearic, and myristic acids) makes up 27 percent of the fat in an egg.[58] The egg white consists primarily of water (88 percent) and protein (11 percent), with no cholesterol and 0.2 percent fat.[59]
There is debate over whether egg yolk presents a health risk. Some research suggests dietary
Type 2 diabetes
Studies have shown conflicting results about a possible connection between egg consumption and type 2 diabetes.
A meta-analysis from 2013 found that eating four eggs per week was associated with a 29 percent increase in the relative risk of developing diabetes.[62] Another meta-analysis from 2013 also supported the idea that egg consumption may lead to an increased incidence of type two diabetes.[63] A 2016 meta-analysis suggested that association of egg consumption with increased risk of incident type 2 diabetes may be restricted to cohort studies from the United States.[64]
A 2020 meta-analysis found that there was no overall association between moderate egg consumption and risk of type 2 diabetes and that the risk found in US studies was not found in European or Asian studies.[65]
Cancer
A 2015 meta-analysis found an association between higher egg consumption (5 a week) with increased risk of breast cancer compared to no egg consumption.[66] Another meta-analysis found that egg consumption may increase ovarian cancer risk.[67]
A 2019 meta-analysis found an association between high egg consumption and risk of upper aero-digestive tract cancers in hospital-based case-control studies.[68]
A 2021 review did not find a significant association between egg consumption and breast cancer.[69] A 2021 umbrella review found that egg consumption significantly increases the risk of ovarian cancer.[70]
Cardiovascular health
One systematic review and meta-analysis of egg consumption found that higher consumption of eggs (more than 1 egg/day) was associated with a significant reduction in risk of coronary artery disease.[71] Another systematic review and meta-analysis of dietary cholesterol and egg consumption found that egg consumption was associated with an increased all-cause mortality and CVD mortality.[72] These contrary results may be due to somewhat different methods of study selection and the use primarily of observational studies, where confounding factors are not controlled.[73]
A 2018 meta-analysis of randomized clinical trials found that consumption of eggs increases total cholesterol (TC),
A 2013 meta-analysis found no association between egg consumption and heart disease or stroke.[79][80] A 2013 systematic review and meta-analysis found no association between egg consumption and cardiovascular disease or cardiovascular disease mortality, but did find egg consumption of more than once daily increased cardiovascular disease risk 1.69-fold in those with type 2 diabetes mellitus when compared to type 2 diabetics who ate less than one egg per week.[63] Another 2013 meta-analysis found that eating four eggs per week increased the risk of cardiovascular disease by six percent.[62]
Eggs are one of the largest sources of phosphatidylcholine (lecithin) in the human diet.[81] A study published in the scientific journal, Nature, showed that dietary phosphatidylcholine is digested by bacteria in the gut and eventually converted into the compound TMAO, a compound linked with increased heart disease.[82][83] Another study found that type 2 diabetes mellitus and kidney disease also increase TMAO levels and that evidence for a link between TMAO and cardiovascular diseases may be due to confounding or reverse causality.[84]
Other
Egg consumption does not increase hypertension risk.[85][86] A 2016 meta-analysis found that consumption of up to one egg a day may contribute to a decreased risk of total stroke.[87] Two recent meta-analyses found no association between egg intake and risk of stroke.[88][89]
A 2019 meta-analysis revealed that egg consumption has no significant effect on serum biomarkers of inflammation.[90] A 2021 review of clinical trials found that egg consumption has beneficial effects on macular pigment optical density and serum lutein.[91]
Contamination
A health issue associated with eggs is contamination by
Health experts advise people to refrigerate washed eggs, use them within two weeks, cook them thoroughly, and never consume raw eggs.[57] 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 so prevalent in the U.S. 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 Salmonella infection is quite rarely induced by eggs. This has not been the case in other countries, however, where Salmonella enteritidis and
Egg shells act as
In 2017, authorities blocked millions of eggs from sale in the Netherlands, Belgium, and Germany because of contamination with the insecticide
Food allergy
One of the most common food allergies in infants is eggs.[99] Infants usually have the opportunity to grow out of this allergy during childhood, if exposure is minimized.[100] Allergic reactions against egg white are more common than reactions against egg yolks.[101] In addition to true allergic reactions, some people experience a food intolerance to egg whites.[101] 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.[102]
Farming
Most commercially farmed chicken eggs intended for human consumption are unfertilized, since the laying hens are kept without
Grading by quality and size
The U.S. Department of Agriculture grades 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).
- U.S. Grade AA
- Eggs have whites that are thick and firm; have yolks that are high, round, and practically free from defects; and have clean, unbroken shells.
- Grade AA and Grade A eggs are best for frying and poaching, where appearance is important.
- U.S. Grade A
- Eggs have characteristics of Grade AA eggs except the whites are "reasonably" firm.
- This is the quality most often sold in stores.
- U.S. Grade B
- Eggs have whites that may be thinner and yolks that may be wider and flatter than eggs of higher grades. The shells must be unbroken, but may show slight stains.
- This quality is seldom found in retail stores because usually they are used to make liquid, frozen, and dried egg products, as well as other egg-containing products.
In Australia[103] and the European Union, eggs are graded by the hen raising method, free range, battery caged, etc.
Chicken eggs are graded by size for the purpose of sales. Some maxi eggs may have double-yolks and some farms separate out double-yolk eggs for special sale.[104]
-
Comparison of an egg and a maxi egg with a double-yolk - closed (1/2)
-
Comparison of an egg and a maxi egg with a double-yolk - opened (2/2)
-
Double-yolk egg - opened
Color of eggshell
Although eggshell color is a largely cosmetic issue, with no effect on egg quality or taste, it is a major issue in production due to regional and national preferences for specific colors, and the results of such preferences on demand. For example, in most regions of the
These cultural trends have been observed for many years. The New York Times reported during the Second World War that housewives in Boston preferred brown eggs and those in New York preferred white eggs.[107] In February 1976, the New Scientist magazine, in discussing issues of chicken egg color, stated "Housewives are particularly fussy about the colour of their eggs, preferring even to pay more for brown eggs although white eggs are just as good".[108] As a result of these trends, brown eggs are usually more expensive to purchase in regions where white eggs are considered "normal", due to lower production.[109] In France and the United Kingdom, it is very difficult to buy white eggs, with most supermarkets supplying only the more popular brown eggs. By direct contrast, in Egypt it is very hard to source brown eggs, as demand is almost entirely for white ones, with the country's largest supplier describing white eggs as "table eggs" and packaging brown eggs for export.[110]
Research conducted by a French institute in the 1970s demonstrated blue chicken eggs from the Chilean araucana fowl may be stronger and more resilient to breakage.[108]
Research at Nihon University, Japan in 1990 revealed a number of different issues were important to Japanese housewives when deciding which eggs to buy and that color was a distinct factor, with most Japanese housewives preferring the white color.[111]
Egg producers carefully consider cultural issues, as well as commercial ones, when selecting the breed or breeds of chickens used for production, as egg color varies between breeds.[112] Among producers and breeders, brown eggs often are referred to as "tinted", while the speckled eggs preferred by some consumers often are referred to as being "red" in color.[113]
Living conditions of birds
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 may lead to pacing and escape behavior.[114]
Many hens confined to battery cages, and some raised in cage-free conditions, are
Laying hens often are euthanized when reaching 100 to 130 weeks of age, when their egg productivity starts to decline.[116] 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 generally are killed soon after they hatch.[117]
In the United States, increased public concern for
Effective 1 January 2012, the
Killing of male chicks
In all methods of egg production, unwanted male chicks are killed at birth during the process of securing a further generation of egg-laying hens.[124] As of June 2023, this practice has been banned in Germany, France, and Italy.[125] Some egg producers have adopted in-ovo sexing, which first became available in 2018.[126] As of September 2023, five companies have commercially available in-ovo sexing technology, which is used for 15 percent of the European layer population.[127]
Cultural significance
A popular
In the New Testament, eggs are referred to as an example of the kind of gift a child might request from their father, and which would not be denied.[129]
In Northern Europe and North America, Easter eggs may be hidden by adults for children to find in an Easter egg hunt. They may be rolled in some traditions.[130]
In Eastern and Central Europe, and parts of England, easter eggs may be tapped against each other to see whose egg breaks first.[131]
Since the sixteenth century, the tradition of a
Fraud
In
See also
- Fish eggs
- Yolkless egg
- Ham and eggs
- List of foods
- List of egg dishes
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- ^ See New York Times historical archive Archived 25 February 2021 at the Wayback Machine for details – link opens on correct page.
- ^ a b "A Blue Story". New Scientist. Vol. 69, no. 989. 26 February 1976. Archived from the original on 5 April 2023. Retrieved 6 April 2011.
- ^ Evidence cited here [2].
- ^ El-banna company website, product information, available here [3] Archived 17 June 2013 at the Wayback Machine.
- ^ Results of the study are published here Archived 11 August 2011 at the Wayback Machine.
- ^ Virtually any on-line chicken supply company will state the egg color of each breed supplied. This Archived 28 November 2011 at the Wayback Machine is one example.
- ^ "Eggs and Egg Colour Chart". The Marans Club. Archived from the original on 29 October 2017. Retrieved 30 October 2017.
- ^ "Scientists and Experts on Battery Cages and Laying Hen Welfare". Hsus.org. Archived from the original on 1 May 2008. Retrieved 10 January 2010.
- ^ "Eggs and force-moulting". Ianrpubs.unl.edu. Archived from the original on 19 October 2008. Retrieved 10 January 2010.
- ^ "Commercial Egg Production and Processing". Ag.ansc.purdue.edu. Archived from the original on 12 October 2009. Retrieved 10 January 2010.
- ^ "Egg laying and male birds". Vegsoc.org. Archived from the original on 6 December 1998. Retrieved 10 January 2010.
- ^ "Free-range eggs". Cok.net. Archived from the original on 24 January 2010. Retrieved 10 January 2010.
- ^ "United Egg Producers Certified". 8 January 2008. Archived from the original on 8 January 2008. Retrieved 22 January 2018.
- ^ "Wondering What The "UEP Certified" Logo Means?". Hsus.org. Archived from the original on 18 May 2008. Retrieved 10 January 2010.
- ^ "Egg Labels". EggIndustry.com. Archived from the original on 4 September 2009. Retrieved 10 January 2010.
- ^ The Humane Society of the United States. "A Brief Guide to Egg Carton Labels and Their Relevance to Animal Welfare". Hsus.org. Archived from the original on 18 May 2008. Retrieved 10 January 2010.
- ^ "EUR-Lex – 31999L0074 – EN". Eur-lex.europa.eu. Archived from the original on 16 June 2011. Retrieved 10 January 2010.
- ^ Vegetarian Society. "Egg Production & Welfare". Archived from the original on 16 March 2018. Retrieved 22 October 2012.
- ^ Torrella, Kenny (1 May 2023). "Save the male chicks". Vox. Retrieved 29 June 2023.
- ISSN 0261-3077. Retrieved 29 June 2023.
- ^ "In-Ovo Sexing Overview". Innovate Animal Ag. Retrieved 21 January 2024.
- ^ Hall, Stephanie (6 April 2017). "The Ancient Art of Decorating Eggs | Folklife Today". The Library of Congress. Retrieved 25 November 2023.
- ^ Luke 11:12
- ^ "History of the Hunt: How an Easter Tradition Was Hatched". English Heritage. Retrieved 25 November 2023.
- ^ Bociąga, Przemysław (7 April 2023). "A Worldwide Easter Tradition With Central European Roots". 3 Seas Europe. Retrieved 25 November 2023.
- ^ "Dancing eggs for Corpus Christi | Barcelona Cultura". www.barcelona.cat. Retrieved 25 November 2023.
- ^ Pomranz, Mike (13 February 2018). "Fake Chinese Eggs Are a Big Problem in India: And they're scarily convincing". MyRecipes. Retrieved 20 April 2024.
- ^ Boehler, Patrick (6 November 2012). "Bad Eggs: Another Fake-Food Scandal Rocks China". Time. Retrieved 20 April 2024.
- ^ LaFraniere, Sharon (7 May 2011). "In China, Fear of Fake Eggs and 'Recycled' Buns". The New York Times. Retrieved 20 April 2024.
- ISBN 978-0-691-21408-5. Retrieved 20 April 2024.
- ISBN 978-1-107-11760-0.
External links
- Fact Sheet on FDA's Proposed Regulation: Prevention of Salmonella Enteritidis in Shell Eggs During Production (archived 17 June 2008)
- Egg Information U.S. Food and Drug Administration (2011)
- Egg Basics for the Consumer: Packaging, Storage, and Nutritional Information Archived 25 May 2014 at the Wayback Machine. (2007) University of California Agriculture and Natural Resources. Retrieved 23 May 2014.