Hidden Allergens in Foods

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Because of the almost unlimited uses of soy, it is a particularly insidious hidden allergen. As with many other allergens, reactions may occur to very small quantities of soy protein, and anaphylaxis to soybean protein has been reported.2,38,39


Soybean lectin is also an important allergen and has been associated with allergic reactions.40


Soybeans may be ingested as whole beans, as flour, or as oil. In addition, soy can be used in the manufacture of food in a great variety of ways, including as a "texturizer," emulsifier, and protein filler. Soy may thus be listed on the ingredient panel according to its use (e.g., "hydrolyzed protein" or "lecithin"39) (Table V).


Soybean flour is often added to cereal flour and is used extensively in the baking industry. The majority of breads contain some soy flour. Pastries, cakes, biscuits, and baby foods may contain soy flour. It is also used in the manufacture of sausages, processed meats, hamburgers, and other meat products" (Table VI). Fermented soybean may be used in the preparation of soy sauce or Worcestershire sauce. Fermented soy is in wide use as a food in the Far East.


Soy is so widely distributed in processed foods that avoidance of soy in the diet is very difficult. Soy may find its way into a food product when added as a "compound" ingredient. For example, if margarine is added to a food product it will be listed as such, but soy present in the margarine itself will not be listed on the ingredients panel.


Soy protein isolate or concentrate may be used to emulsify fat in food products and may thus be used in the manufacture of ice cream, mayonnaise, and a variety of other liquid fat- or oil-containing foods. The concentrate or isolate may also be used in soy milk and as a protein concentrate added to health foods and high-protein biscuits. Other foods that may contain soy include pureed and cereal baby foods, margarine, and white and brown bread39 (Table VI).


Other uses for soy include the manufacture of tofu (soybean curd), which may in turn be used for the manufacture of soy-based ice cream. Soy may be converted into products having a meat-like texture.41 This "textured vegetable protein" is used in simulated meat products or may be added to meat as an extender. These products are often used as meat substitutes in vegetarian products and in catering establishments, including hospital and army food services, and feeding programs.


The seeds of soybeans are widely used as a source of oil. The oil has many uses (e.g., in salad dressings, margarine, baby foods, industrial components, linoleum, paint, plastics, soap, and glue for plywood) (Table VII). Although soybean oil was initially thought to be safe for soy-sensitive individuals,42 it is now evident that soy protein may occur in soybean oil.43 Thus the allergenicity of soybean oil would depend on its purity, which in turn depends on the extraction process. Recent evidence has demonstrated that although oxidized soybean oil may not show allergenicity, proteins in soybeans are capable of interacting with oxidized lipid to form products that are allergenic to soybean-sensitive patients.44 Indeed, Hiyama et al.45 report a case of urticaria associated with paren-teral nutrition with an intravenous 10% lipid emulsion containing a soybean oil base. Such reactions, however, appear to be uncommon, and there are very few reports of this nature in the literature.


Soy products are often purchased by those specifically avoiding cow's milk, often with the assumption that a soy-based product is free of cow's milk protein. This may not always he true, and caution is required. Again, labels should be read carefully, and they should, of course, contain the correct declaration.


Thickeners, stabilizers, emulsifiers, and bulking agents may be manufactured from a variety of other members of the legume family in addition to soybeans. On the basis of in vitro studies, Barnett et al.46 suggested that there may be cross-reactions between soy and other members of the legume family (Table VIII). Further evidence for broad cross-reactivity has been provided by RAST and skin prick tests: however, it is rare to have symptomatic reactivity to more than one member, and clinical hypersensitivity to one legume does not require elimination of the entire legume family.47,48 Carob, derived from the carob bean. is used commonly as a chocolate substitute, and one should possibly guard against cross-reactivity to this legume. Peanut sensitivity is discussed below.


Labels that may indicate the presence of soy protein

Gum arabic
Bulking agent
Guar gum
Hydrolyzed vegetable protein (HVP)
MSG (Monosodium glutamate) !
Protein extender
Soy Flour
Soy nuts
Soy panthenol
Soy protein
Soy protein isolate or concentrate
Soy sauce
Soybean oil
Textured vegetable protein (TVP)
Vegetable broth
Vegetable gum
Vegetable starch
References 39,90,92
* Mostly produced from soy but may be manufactured from egg.
! Sometimes produced from soy or wheat but now mostly by synthetic means.39


Foods that may contain soy protein

Baby foods
Bakery goods*
Black pudding
Bread (esp. high-protein bread)*
Breakfast cereals (some)
Burger patties
Butter substitutes
Canned meat or fish in sauces*
Canned or packaged soups*
Canned tuna
Cheese (artificial) made from soybeans*
Chinese food
Chocolates (cream centers)
Cooking oils
Gravy (sauce) powders
Hamburger patties
Hot dogs
Hydrolyzed vegetable protein (may be wheat)
Ice cream
Infant formula (including cow's milk formula)
Liquid meal replacers
Meat products (e.g., sausages, pastes. Vienna sausages [wieners])
Pies (meat or other)*
Powdered meal replacers
Salad dressings
Sauces (e.g.. Worcestershire, sweet and sour, HP.,Teriyaki)
Seasoned salt
Snack bars
Soy pasta products
Soy sauce
Soy sprouts (Chinese restaurants)
Stews (commercial)
Stock cubes (bouillon cubes)
TV dinners
References 39,90,91

* May be present because of soya in the flour used.


Other sources of contact with soy

Body lotions and creams
Dog food
Enamel paints
Fabric finishes
Flooring materials
Printing inks
Reference 93


Members of legume family

Aduki beans
Broad bean
Black turtle bean
Black-eyed bean
Chick pea
Fava bean
Garbanzo bean
Great Northern bean
Green bean
Kidney bean
Lima bean
Mung bean
Navy bean
Pinto bean
Snap bean
String bean
Wax bean
Other members
Alfalfa (sprouts)
Acacia (gum)
Carob (chocolate substitute)
Cassia or senna (in laxatives, curry, cinnamon)
Fenugreek (used in curries, cinnamon,
  primary flavoring in imitation maple syrup)

Masur bean
Green pea
Purple-hull pea
Senna or cassia (in laxatives and Epsom salts)
Tragacanth (gum)
References 46,47,90



Wheat is the most allergenic of all cereals. lgE antibodies have been demonstrated lo many components of wheat kernels, including albumin, globulin, gliadin, wheat germ agglutinin, a concanava-lin A-purified glycoprotein, and a trypsin inhibitor.49-52 Wheat is most rich in gluten, with the other grains containing a lesser mixture of gluten and gliadin. In addition to being present in all wheat-based food products, wheat gluten is frequently added to baked products made from other grains, including those made from soy flour.


Wheat-sensitive individuals should avoid a product that includes other flours, because it is likely that at least some wheat flour or a derivative will also be present.53 Even "gluten-free" bread may contain small amounts of part of the wheat family.49,56 Spelt may better be described as nonhybridized wheat.56 No data have indicated differences in the allergenic profiles of the various wheat varieties, and they should all be viewed as potential allergens.


Hydrolyzed wheat proteins can be used in processed foods for flavoring purposes (e.g., in meat flavorings) or as a binder in vegetarian burgers. In the United States legislation dictates that this form of wheat must be labeled as wheat-derived, but this is not always the case in other countries. Wheat can appear under various names on ingredient panels (Table IX) and can be found in many food products (Table X). Gluten finds its way into a few pharmaceutical products (e.g., Dimetapp LA, Nu-lacin, and Fybranta).57


Buckwheat is not a member of the grass family and is thus not a true cereal.58 The grain may be used for human food in various forms from pancake flour to buckwheat noodles and baby foods58


For the wheat-hypersensitive individual, products made from oats, rice, rye, barley, or corn or speciality foods made for gluten-sensitive individuals generally may be used instead of wheat. However, cross-reactions, although unusual, may occur between wheat, barley, rye, maize, rice, and sorghum,8,59,60 as well as between the pollens of cereals and cereal flours.61


Labels that may indicate the presence of wheat protein

All-purpose flour
Bleached flour
Bulgur (cracked wheat)
Durum wheat
Enriched flour
Gelatinized starch* (or pre-gelatinized)
Graham flour
Hard durum flour
High gluten flour
High protein flour !
Hydrolyzed vegetable protein !
Miller's bran
Modified food starch*
Modified starch*
MSG (monosodium glutamate)**
Unbleached flour
Vegetable gum*
Vegetable starch*
Vital gluten
Wheat bran
Wheat flour
Wheat germ
Wheat gluten
Wheat starch
White flour
Whole wheat
Whole wheat flour
References 48,49,54,55,57,80,90

* May indicate the presence of soy protein50
    or may he manufactured from cassava (tapioca), maize, or rice.
! Sometimes produced from soy or wheat but now mostly by synthetic means.
** May be soy.


Foods that may contain wheat

Alcoholic beverages
(made from grain alcohol) Ale
Baked goods
Biscuits Breads (including rye bread)
Crackers, etc.
Baking mixes
Barley bread and drinks
Battered foods
Bouillon cubes
Breaded meats
Breaded vegetables
Breakfast cereals
Candy or chocolate candy
Canned processed meat
Cereal grains
Hot dogs
Ice cream
Ice cream cones
Luncheon meats
Malted milks (e.g., Horlicks)
Milk shakes
Noodle products
Pasta (noodles, spaghetti. macaroni)
Pepper (compound or powdered flour filler)
Processed meats
Snack foods
Soup mixes
Soy sauce
References 57,90,91



Peanuts are one of the most allergenic foods,62,63 and peanut allergy is one of the most common food allergies.64 Peanuts are probably the most common cause of death by food anaphylaxis in the United States, and about one third of peanut-sensitive patients have severe reactions to peanuts.65,66 Peanuts are added to a large variety of processed foods (Table XI). These include ice cream (as a flavoring), marinades, snack foods, and biscuits. Peanuts can be used as a flavoring or a seasoning agent67 and may be labeled as such (Table XII). Nuts may be used in the manufacture of vegetable burger patties.68 A fatal reaction to peanut antigen in almond icing has been recorded.69 Peanut butter may also be used to "glue down" the ends of egg rolls to keep them from coming apart.70 Some individuals do not know that peanut butter is commonly used in Oriental cooking.


Peanuts can be "deflavored," "reflavored," and pressed into other shapes such as almonds and walnuts.9,65 These products retain the allergenicity of the peanut. Some patients with peanut allergy also react to sweet lupine seed flour, which may be used, for example, to fortify a spaghetti-like pasta.71


Although uncommon, a peanut protein hydrolyzate may also be used in soft drinks as a foaming agent or in confections as a whipping agent.67


Peanut oil has been considered to be devoid of allergenicity,72,73 and this was initially confirmed by double-blind crossover studies.74 However, peanut oil allergenicity is clearly process-related, because cold-pressed peanut oils may contain peanut allergen.75 Moneret-Vautrin et al.76,77 confirmed the allergenicity of peanut oil in milk formulas, and 11 of 45 brands of milk formulas in France contained variable amounts of peanut oil.77 Residual peanut proteins arc believed to become more allergenic with heating.77


The oil is frequently used in the preparation of so-called "health foods." The oil can be used for many nonfood products, which may, on contact, affect sensitive individuals. Like peanut oil, other vegetable oils such as soy, maize, sesame, and sunflower oils contain very low quantities of protein.78,79


Individuals who are allergic to peanuts are said to not be allergic to nuts such as almonds, pecans, or walnuts; and these nuts can be substituted for peanuts.9 This is contradicted by a recent study, which showed that 50% of individuals allergic to peanuts reported allergic reactions to other nuts as well.70 These findings were not validated by further clinical investigation.


Foods that may contain peanut or peanut oil.

Baked goods
Baking mixes
Battered foods
Breakfast cereals
Cereal-based products
Chinese dishes
Egg rolls
Ice cream
Milk formula
Peanut butter
Satay sauce and dishes
Thai dishes
Vegetable fat
Vegetable oil
References 66,70,72


Labels that may indicate the presence of peanut protein

Peanut butter
Emulsifier (uncommon)
Oriental sauce
Reference 67



Fish are one of the most common causes of food allergy, particularly in adults and in Scandinavian countries.9 Fish may find their way into processed foods in raw, powder, or oil form. In the majority of instances, this substance is clearly labelled as "fish" or with another obvious descriptor. However, fish allergens may be found unlisted if added as part of an oil. Fish products are not usually hidden ingredients but may be hidden in Caesar salad dressing or in Worcestershire sauce if it contains anchovies.9


Some seafood flavors (e.g., shrimp) arc added to food in the form of a powder manufactured from the seafood's shell. Shrimp antigen II is heat stable."' A variety of antigens are shared by several crustaceans including shrimp, prawns, crabs, lobsters, and crayfish (crawfish).


At present, some manufacturers are researching the possibility of adding fish meal (flour) to bread as a source of omega-3-fatty acids (personal communication, M. M. Melnyczuk). Skin prick tests and RASTs indicate extensive cross-reactivity among fish species, but recent research suggests that patients may be able to consume some species of fish despite positive test responses to one or two.81 However, it is generally recommended that patients allergic to fish avoid all fish species.


A major difficulty in identifying a food allergen in some patients is that they may he unaware of the connection between a specific food and allergic symptoms, because the symptoms may appear much later.13,14 Although clinical history and routine laboratory studies have great predictive value in most individuals with food allergy, they may have little value in predicting which foods are responsible in many others, particularly in adults.64,82,83 Moreover, in some individuals with a history of a reaction to food, there may be poor correlation between history and results of skin tests, in vitro blood tests, and double-blind, placebo-controlled food challenges.64,84-86 The double-blind, placebo-controlled food challenge remains the gold standard in the diagnosis of food hyper- sensitivity, and in the event of negative skin prick test and RAST results, may be the only method with which to confirm a food hypersensitivity.87,88


One clear message from the literature is that most fatal and near-fatal reactions happen when eating away from home.2,3,11,69,89 Individuals with severe food hypersensitivity should probably avoid processed foods. If it is necessary to purchase these foods, they should be made by a reliable manufacturer. Parents and children can learn to scrutinize food labels carefully. Unfortunately, the multiplicity of possible names for any one ingredient may let a hidden allergen slip by. If possible, hypoaller-genic formulas should be tested in each case before being prescribed for children sensitive to cow's rnilk.35,36 The very sensitive individual should wear a Medic Alert bracelet and carry an epinephrine (adrenaline) self-injector at all times.1 Less sensitive individuals may need to carry antihistamincs with them.


Fortunately, many individuals lose their reactivity to foods over time, albeit not completely in some. Bock89 recommends careful and periodic challenges in these patients to save families from prolonged anxiety about accidental ingestion. Unfortunately, sensitivity to peanut is seldom outgrown.66


Acknowledgement should be made to the food industry for the strides made in improved labeling of food products, in many countries, the food industry has played a leading role in constructing food intolerance databases, which can assist sensitive individuals in avoiding foods containing a particular ingredient. In the long term, manufacturers must he persuaded to bring common ingredient names into use, and legislation should be passed to make food labels more accurate. A possible solution would he to list the derivative in brackets after the ingredient, for example, ovomucoid [egg].


I thank Dr. Sarah Ruden (Department of Classics, University of Cape Town). Prof. Eugene Weinberg (Allergy Clinic, Red Cross Children's Hospital, Ronde-bosch). Prof. Paul Potter (Allergology Unit. University of Cape Town Medical School. Observatory). Tanya and Mikhailo Melnyczuk of Roberts & Melnyczuk Food Research & Development Consultants, and Ronn Timm (South African Association of Food Scientists and Technologists and Royal Beechnut Pty. Ltd.) for their advice and expertise.


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