Egg yolk

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Code: f75
Latin name: Gallus spp.
Source material: Freeze-dried egg yolk

Allergen Exposure

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 unfertilised, since the laying hens are kept without any roosters. Fertile eggs may be 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. 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. Hen’s egg is comprised of about 8-11% shell, 56-61% white and 27-32% yolk. (1, 2, 3, 4, 5) In addition, the protein in raw eggs is only 51% bio-available, whereas cooked egg protein is nearer 91% bio-available, meaning the protein of cooked eggs is nearly twice as absorbable as the protein from raw eggs. (1, 6)

Foods that may contain egg include salad dressings, breads, breaded foods, muffins, pancakes, waffles, meringues, marshmallows, prepared soups and beverages, frostings, ice creams and sherbets, pie fillings, sausages, prepared meats, mayonnaise, coatings and breading for fried foods, tartar and hollandaise and other sauces.

Egg yolks are used to make mayonnaise and other dishes high in fat. Egg yolks are important as binding agents in many preparations in European cooking due to the emulsifying action of lecithin. This property is crucial for mayonnaise and sauces such as Béarnaise, and hollandaise; custards such as crème anglaise, crème brûlée, crème caramel, lemon custard and key lime pie; and meat dishes such as pâté and meatloaf. (1)

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 white is used in desserts such as meringues and mousse. (1)

Foods that may contain egg include candy, salad dressings, breads, breaded foods, muffins, pancakes, waffles, meringues, marshmallows, prepared soups and beverages, frostings, ice cream and sherbets, pie fillings, sausages, prepared meats (sausages, patês) (egg as a binding agent), mayonnaise, coatings and breading for fried foods, tartar and hollandaise and other sauces.

Egg yolk is an important emulsifier agent in the food industry.

Allergen Description

The total number of egg proteins is not known, but more than 40 have been suggested for Egg white alone, (7) and up to 24 different antigenic protein fractions have been isolated.

Although the main allergens in egg are found in the Egg white, Egg yolk also contains a large number of specific IgE-binding allergens. (8) Three proteins (apovitellenins I & VI and phosvitin) have been shown to bind IgE from the sera of persons with specific IgE to Egg yolk. (5) Both common and distinct allergenic molecules are present in egg. This was demonstrated in a study of 11 patients with a history of egg allergy, in whom all sera reacted positively to both Egg white and Egg yolk. Eight patients reacted equally or more strongly to Egg white, and even though each could inhibit the IgE binding of the other to some degree, Egg yolk could only be partially inhibited by Egg white in eight sera. (9)

Allergens have also been found in hen and chicken meat (flesh) and sera. (10)

Egg yolk allergens characterised to date:

Allergen name

Nomen-clature

Size

Stability

Refs

alpha-livetin, Livetin, Serum albumin

Gal d 5

 

partially heat-labile

(11, 12, 13, 14, 15 16)

YGP42, a lipoprotein

Gal d 6

35 kDa

heat stable

(12, 17, 18)

Apovitellenin I, Apovitellenin-1

 

 

 

(5, 19, 20)

Apovitellenin VI

 

 

 

(15, 17)

Gal d Phosvitin

 

 

 

(15, 17)

 

Gal d 5 is a partially heat-labile allergen that may cause both respiratory and food-allergy symptoms in patients with bird-egg syndrome. (12, 21)

Gal d 6, a recently-characterised Egg yolk allergen, was detected in 5 of 27 (18%) egg-allergic patients. The Egg yolk allergen had a molecular weight of 35 kDa. Heating and reduction treatments did not affect its allergenicity, although digestion with simulated gastric fluid diminished the IgE-binding capacity of the allergen. The N-terminal amino acid sequence corresponded with the YGP42 protein, a fragment of the vitellogenin-1 precursor. (18)

See individual allergens for further specific information: Gal d 1, f233; Gal d 2, f232; Gal d 3, f323; Gal d 4, k208.

Potential Cross-Reactivity

Although cross-reactivity between Egg white and Egg yolk is not common (unless either has contaminated the other), some degree of cross-allergenicity has been demonstrated between hen's Egg white and Egg yolk proteins, signifying that there are a number of common allergenic determinants on these egg proteins. (5)

Serum IgE from patients with bird-egg syndrome has been shown to recognise a 70 kDa protein in Egg yolk (alpha-livetin) and some major allergens in bird feather extract (proteins of 70, 95, and 200 kDa). An examination of pooled sera from patients with bird-egg syndrome with budgerigar or hen feather extract and Egg yolk extract respectively demonstrated complete blocking of IgE binding to allergens in Egg yolk and bird feather extract, suggesting cross-reactivity. However, serum IgE from patients with Egg white allergy did not react with allergens in Egg yolk and bird feather extract, despite strong IgE binding to Egg white allergens. Therefore, common epitopes exist between budgerigar, hen feather and Egg yolk alpha-livetin. The authors suggest that alpha-livetin (chicken serum albumin) leads to a cross-sensitisation, and the development of the ‘bird-egg syndrome.’ (14)

There is cross-reactivity between Egg white from Chicken and Turkey, Duck, Goose and seagull Egg white. (10) However, this would depend on a specific cross-reactive allergen component: patients with an IgE-mediated allergy to Egg white from Duck and Goose may not necessarily be allergic to hen’s egg. (22)

Clinical Experience

IgE-mediated reactions

Hen’s egg is one of the most frequent causes of immediate food allergy in infants and young children. Egg white is generally more allergenic than Egg yolk. Clinical reactions to egg are predominantly IgE-mediated, immediate reactions, characterised by atopic dermatitis, urticaria, angioedema, vomiting, diarrhoea, rhinoconjunctivitis and asthma. Children with atopic dermatitis may have an immediate exacerbation of symptoms, or a delayed reaction causing a worsening of their dermatitis 1-2 days after exposure to egg. Delayed reactions are possible and are generally not IgE-mediated, and are probably caused by T-cell sensitisation. Eosinophilic esophagitis as a result of allergy to egg has been described. IgE-mediated sensitivity to egg proteins in egg-processing workers has been reported.


Hen’s egg is one of the most frequent causes of immediate food allergy in infants and children, affecting about 1-2% of preschool children; but it also commonly affects adults. (23, 24, 25, 26) Few studies on the prevalence of egg allergy have been performed. An observational study of 4 000 Spanish patients who consulted an allergist found that egg allergy accounted for 16% of food allergies in the general population, and that egg was the fourth most frequently implicated food. In the subgroup of children aged less than 5 years this frequency was 44%; and, together with milk, egg was the main cause of sensitisation. (27) In another Spanish study of 355 paediatric patients with food allergy, the prevalence of allergy to egg proteins was 20.1%. (28)

Clinical reactions to egg are predominantly IgE-mediated, immediate reactions characterised by atopic dermatitis, urticaria, angioedema, vomiting, diarrhoea, rhinoconjunctivitis and asthma. (24, 29, 30, 31, 32, 33, 34) Isolated respiratory symptoms are infrequent, and are almost always associated with cutaneous or digestive symptoms. Respiratory symptoms after egg ingestion are more frequent in patients sensitised to bird proteins (bird-egg syndrome). (20) Children with atopic dermatitis may have an immediate exacerbation of symptoms or a delayed reaction causing a worsening of their dermatitis 1-2 days after exposure to egg. Acute dermatological manifestations consist of erythema, urticaria and angioedema clearly associated with egg ingestion. The onset of symptoms may be rapid, developing a few minutes after ingestion of the causative allergen. 93% of positive egg challenges elicited immediate symptoms, even though the child had not previously ingested egg. Symptoms developed within the first 20 minutes of egg ingestion, and 53% of the children presented cutaneous symptoms in the following order of frequency: pruritus, erythema, urticaria and angioedema. (35) Delayed reactions are generally not IgE-mediated and are probably caused by T-cell sensitisation. (36) Eosinophilic esophagitis as a result of allergy to egg has been described. (37, 38, 39 )Egg has also been frequently associated with childhood asthma. (40) Food-sensitive enteropathy may be caused by a number of foods, including egg. (41) Patients with oral allergy syndrome due to egg hypersensitivity have also been reported (one patient being monosensitised to egg). (42, 43)

Importantly, egg-allergic children may occasionally develop contact urticaria to hen's egg and yet have no overt symptoms on ingestion. It has been suggested that oral tolerance to ingestion of Egg white may be a result of the allergens being involved in skin contact reactions being unstable to digestive enzymes; they are therefore broken down more easily. (44)

Allergy to egg is generally agreed to be one of the most common causes of food allergy in infants and young children. Some researchers have reported that in egg-allergic children, IgE antibodies were found in more than 65% of children with eczema and respiratory tract symptoms. (45) However, few studies have differentiated between allergies to whole egg, Egg white and Egg yolk.

In a study of 674 patients referred to an allergy unit in Spain, the prevalence of food allergy was found to be 9.1%. The foods most frequently involved in allergic reactions were fruits (56.6%) and tree nuts (22.6%). However, Egg white was implicated in about 10% of the food allergy group. (46)

Egg yolk has been implicated in adult patients with eosinophilic esophagitis (EE). In a study of 16 men and 7 women aged 18-57 years, 17 of 21 patients were polysensitised to several different environmental allergens, and 19 of 23 (82%) had serum IgE specific for one or more food-associated allergens. Of these, 17% were sensitised to Egg yolk and 30% to Egg white. (45)

Sensitisation and symptoms to inhaled Egg-white allergens may occur: IgE-mediated sensitivity to egg proteins has been reported in egg-processing workers (47) as well as in bakers. (48)

It has been suggested that egg intolerance in adults is due to sensitisation to Egg yolk livetins and can be provoked by inhalation of tame bird dander (bird-egg syndrome), and thus is not the same as Egg white allergy in atopic children. (12) A case report described an elderly woman who became egg allergic as a result of inhalant allergen sensitisation from a parrot. The patient revealed high levels of IgE antibodies to Egg yolk and to various bird sera. (49) A case report of reactivity to Egg yolk as a result of avian serum sensitisation was published, the authors suggesting that given the results of the case, it may be clinically relevant to test patients with a history of exposure to birds for both Egg yolk and bird serum allergies. (50)

Specific oral tolerance induction for whole egg in school-age patients with severe egg allergy has been conducted successfully. (51) Few studies with Egg white have been published, (52) although children desensitised to whole egg were demonstrated to have diminished reactivity to Egg white. (53)

 

Compiled by Dr Harris Steinman, developer of Allergy Advisor, harris@zingsolutions.com

Citing This Page

Steinman HA. f75 Egg yolk. http://www. phadia.com/en/Allergen-information/ImmunoCAP-Allergens/Food-of-Animal-Origin/ Egg/Egg-yolk/. Accessed (date to be filled in).

 

References

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Updated 2010

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.