Hidden Allergens in Foods

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Reproduced from
Steinman HA. Hidden allergens in foods.
Journal of Allergy and Clinical Immunology 1996;98(2):241-250
with permission from Mosby-Year Book, Inc.
Selected by the SciLinks program, a service of National Science Teachers Association. Copyright 1999-2002.

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Deaths in children, adolescents, and adults who ingested foods to which they were highly allergic have been reported.1,2 These deaths are often caused by a "hidden" ingredient in the food to which the individual is allergic.1,3 Yunginger1 suggests that in the United States, more children and adolescents die annually as a result of food-induced anaphylaxis than as a result of insect stings. The majority of these deaths are due to severe allergy to peanut and nuts, and asthma appears to be an important risk factor for this form of allergy.2


Sensitivity can occur by ingestion of minute quantities of food allergens4,5 and even by inhalation of food allergens carried in air or in cooking fumes.6-12 The association between a reaction and a food may not initially he obvious because many patients experience a reaction only several hours later.13,14 Unlike the very acute and often dramatic reaction to peanut, the form of reaction to egg, milk, wheat, and soy may he through "soft signs" (e.g., gastroenteropathies, asthma, and atopic dermatitis).12 Other diagnostic difficulties occur in individuals experiencing anaphylactoid reactions and in patients with food-dependent exercise-induced anaphylaxis. 15


Reasons for allergens being Hidden in foods

Probably the most common reason for sensitive individuals to ingest a hidden allergen is contamination of a safe food. This occurs when the same serving utensils are used for different foods. Salad bars and ice cream parlors offer good examples of this practice. It also occurs when deli meat slicers are used for slicing both cheese and meat and when manufacturers use previously manufactured products for manufacture of a secondary product. Mayonnaise used in the manufacture of a new product may not prompt the listing of mayonnaise or egg. particularly if this ingredient is less than 2% of all the ingredients in the new product. Another form of contamination occurs when a manufacturing plant uses the same equipment to make different products, such as ice cream and milk-free sorbet, without adequate cleaning of the equipment16 or when the same oil is used for cooking French fries and fish in a take-away outlet.12


There are many other ways for allergens to he hidden in food. Misleading labels may disguise hidden allergens. This can he illustrated by nondairy creamers or coffee whiteners, which contain skim milk17 or by meat products that contain soy. Some margarine, claiming to consist of 100% corn oil, may in fact contain skim milk powder. A drink advertised for "people who cannot drink milk" is actually milk with lactase enzyme for individuals with a lactose intolerance, but it clearly still contains milk protein.


Hidden allergens can also occur in processed food when an ingredient is added for a specific application; for example, when egg is used in food products and is listed on the ingredient panel as a binder, protein, or emulsifier. This may also occur when soy is used for its "texturizing" or emulsifying properties. Natural flavors such as pineapple, milk casein, or hydrolyzed soy protein may be used and listed as flavoring or natural flavoring, as in microwave popcorn.


Ingredient switching is another source of concern and may happen when manufacturers change ingredients without making this clear on the label. This can transpire when a shortage of vegetable oil results in substitution with a tropical oil, or as noted previously, when a margarine manufacturer advertises 100% corn oil but adds skim milk without altering the label.


Mistakes take place when consumers assume that a brand of food that uses similar labels for a range of products has similar formulations. Loopholes in labeling regulations allow allergens to be hidden in a food product when a manufacturer is excused from listing an ingredient that is present at less than a specific percentage of the total product.


Another major problem is that a food may be listed on the product label by an uncommon term. This practice is addressed in this article.


Food manufacturing practices vary throughout the world, and because the importation of food is common practice, this review aims to assist the individual with allergies and the traveller by including in the tables as many sources of hidden food allergens as possible.


Problems relating to some specific foods


Egg is one of the most allergenic of all foods, and minute amounts of egg can result in symptoms within minutes, including life-threatening anaphylaxis. This is also seen after contact with egg through non-oral routes.6,18-20 Reactions may occur the first time a child is given egg.21 Although ovalbumin, ovomucoid, and ovotrans-ferrin have been identified as the major allergens in egg white,21,10 other unnamed allergens of lesser importance have been identified.22 These allergens are also present in egg yolk but in lesser quantities.21


This is important because components of egg may be individually used for specific actions in food preparation. For example, hen's egg lysozyme is used as a preservative in food; and in some countries, notably Japan and Switzerland, lysozyme is used in medications.23,24 Individuals sensitive to hen's egg have been shown to be allergic to lysozyme produced from hen's egg.18,23-26


A variety of descriptions may indicate the presence of egg protein in a product (Table 1). The function that egg performs in a product may be named on the ingredient panel (e.g., binder, emulsifier, or coagulant). Because legislation may permit a manufacturer not to list an ingredient constituting less than a specific percentage of the total product, noodles containing egg may not have egg listed on the ingredient panel. A similar situation may occur when egg white is used to give pretzels, bagels, and other baked goods their shiny appearance. In most products, lecithin is derived from soy, but sometimes it may be egg-derived. Provitamin A (extracted from egg) may be used and described as a colorant, but its antigenic properties are unknown.


In addition to food products (Table 2) that may be dangerous to egg-sensitive individuals, egg proteins are also found in cosmetics, shampoos, and pharmaceuticals, such as the laxative Agarol. A patient allergic to egg should avoid buying fried foods from vendors who use the same frying surface for preparing multiple types of food. Recent evidence suggests that egg-sensitive children can receive measles immunization safely.27


Although rare, avian proteins can induce egg allergy in susceptible individuals.28-31 It has been suggested that duck egg be substituted for hen's egg in egg-sensitive individuals. These individuals are able to tolerate cooked chicken.32


Labels that may indicate the presence of egg protein

Egg white
Egg yolk or yellow
Powdered egg
Whole egg
References 32,37,80,90


Foods that may contain egg protein

Baked goods (most except some breads)
Baking mixes
Bearnaise sauce
Bouillon (in restaurants to clear it)
Breakfast cereals
Cake flours
Candy (see Sweets)
Creamy fillings
Egg noodles
French toast
Hollandaise sauce
Ice cream
Lemon curd
Malted cocoa drinks (e.g., Ovaltine, Ovamalt)
Noodles (egg)
Processed meat products (e.g., bologna, meat loaf, meatballs, sausages)
Salad dressing (creamy)
Sweets (e.g., fondant creams, truffles, marshmallows, etc.)
Tartar sauce
Turkish Delight
Wines (if cleared with egg white)
References 32,91



Patients with very sensitive milk allergy can react to a very small quantity of milk protein, including minor contamination13 and even inhalation of milk powder.7


Milk may be found in a large variety of processed foods (some obvious and others not), including confections, margarine, cheese, and pies (Table III). Cheese and cream contain milk protein and should be avoided. Milk contamination of a product is possible if the same manufacturing equipment is used for various products. There is also a carryover effect when one product is used in the manufacture of another.16 In addition, patients should be careful when ordering sliced products from outlets that use the same slicers for cutting a variety of foods (e.g., cheese and cold meat). Lactose, which may contain residual milk protein,may be found in foods and as a filler in the manufacture of medicines such as Benadryl capsules (United States).


Hypoallergenic milk formulas have been used as a milk replacement for children with milk hypersensitivity. However, hypoallergenic milk formulas are not non-allergenic, and many children react to these, depending on the particular formula.33-36


Common descriptions on ingredient panels are "milk," "pasteurized milk," "full cream milk powder," "dried milk," and "skim milk powder" (Table IV). Extracted milk proteins added to foods retain their antigenicity and may be described as "casein," "caseinate," "whey," or "whey powder."

In our community, many individuals consider skim milk and skim milk powder not to be milk and substitute these for milk. In some instances milk is used in emulsions and can be described as "caseinate," "emulsifier," or "protein."


Soy products are often purchased by those specifically avoiding cow's milk, with the assumption that a soy-based product is free of cow's milk protein. This is not true. "Vegetarian" cheese may contain cow's milk protein. This term simply means that the rennet used in its manufacture is of vegetable origin.37


Foods that may contain milk protein

Batter-fried foods
Breakfast cereals
Cream sauces
Cream soups
Fish in batter
Gravies and gravy mixes
Ice cream (and "non-milk" fat)
Imitation sour cream
Instant mashed potatoes
Other baked goods
Packaged soups
Soy cheese
Soup mixes
Canned soups
Vegetarian cheese
References 17,32,90,91


Labels that may indicate the presence of milk protein

Artificial butter flavor
Butter fat
Buttermilk solids
Caramel color
Caramel flavoring
Cream Curds
"De-lactosed" whey
Demineralized whey
Dried milk
Dry milk solids
Fully cream milk powder
High protein flavor
Lactalbumin phosphate
Milk derivate
Milk protein
Milk solids
Natural flavoring
Pasteurized milk
Rennet casein
Skim milk powder
Sour cream (or solids)
Sour milk solids
Whey powder
Whey protein concentrate
References 32,80,90


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