"Numerous studies have described alterations in allergens as a result of processing or cooking. Various types of processing (e.g., heating, milling, fermentation) may alter the antigenic properties of allergens because these processes can affect the three-dimensional structure of proteins and thus the IgE binding epitopes. The type and extent of structural alterations may vary depending on the processing method. This is especially true for conformational epitopes because they are dependant on tertiary structure (Cooke and Sampson, 1997; Vila et al., 2001). For many food allergens, processing effects are inherent in the data used to characterize thresholds because the test articles used in DBPCFCs are processed. For practical reasons, the test material must be concealed in some way for the study to be "blinded." For example, the taste of peanut butter or peanut flour must be disguised in DBPCFCs for peanut allergies. Preparation of the test material typically involves cooking or processing of the allergenic food. In addition to altering existing epitopes, processing might also induce chemical or structural changes that result in the formation of new antigenic epitopes, or neoantigens (Maleki, 2004).
Altered antigenic reactivity is most commonly assessed by measuring changes in the binding of antibodies to extracts of raw and processed foods. Reduced or enhanced IgE binding in such studies would suggest that the threshold for an allergic reaction could be affected by processing. However, definitive proof of an altered threshold requires DBPCFC testing.
The effects of processing on some specific major allergens have recently been reviewed, and are discussed below (Besler et al., 2001; Poms and Anklam, 2004). Variable patient responses make it difficult to conclude that a particular processing or cooking procedure affects allergenicity in all cases.
Peanuts. Extracts of roasted peanuts have been shown to bind IgE from patients at 90-fold higher levels than do similar extracts of raw peanuts in competitive, IgE-based ELISAs (Maleki et al., 2000). Using immunoblot techniques, two of the major allergenic proteins in peanut, Ara h 1 and Ara h 2, were shown to be highly resistant to heat and gastrointestinal digestion following treatment in the Maillard Reaction (which occurs during the processing or browning of foods in the presence of heat and sugars). Earlier studies also observed increased IgE binding and altered IgE epitopes in roasted versus raw peanuts (Nordlee et al., 1981). The allergenic proteins Ara h 1, Ara h 2, and Ara h 3 from fried or boiled peanuts bound significantly less IgE than the same proteins from roasted peanuts (Beyer et al., 2001), even though there were similar amounts of the allergenic proteins in peanuts processed by each method. These studies suggest that thresholds for boiled or fried peanuts may be higher than for roasted or raw peanuts, at least for the three major peanut allergens. In practical terms, the vast majority of peanuts consumed whole or in processed foods in the U.S. are roasted. Boiled or fried peanuts are an ethnic or regional specialty and are usually eaten whole, rather than as a component of processed foods.
Milk. Pasteurization and homogenization did not reduce allergenicity in skin prick tests or DBPCFC (Host and Samuelsson, 1988). However, boiling milk for 10 minutes reduced IgE binding of the allergenic proteins alpha-lactoglobulin and casein by 50 to 66% and eliminated beta-lactoglobulin and serum albumin reactivity in skin prick tests (Besler et al., 2001; Norgaard et al., 1996). Hypoallergenic infant formulas produced from heat denatured or enzymatically hydrolyzed caseins or whey proteins showed reduced allergic reactivity by immunoblot, RAST, and DBPCFC in most milk-allergic children. However, some severe reactions have been reported (Sampson et al., 1991; Saylor and Bahna, 1991). Maillard reaction products in milk are reported to have increased allergenicity in skin tests (Maleki, 2004). Allergic reactions have also been reported involving both hard and soft cheeses (Besler et al., 2001).
Egg. Both soft and hard boiling of eggs decreased, but did not eliminate, antigen binding of rabbit antiserum to ovomucoid and ovalbumin (Besler et al., 2001). Heated egg white showed a 58% decrease in IgE binding in RAST (Anet et al., 1985). A decrease in positive reactions was seen with heated egg white in 55% of egg allergic patients using DBPCFC (Urisu et al., 1997). There are reports of allergic reaction to egg contained in cooked meatballs or hamburger (Sampson et al., 1992b; Besler et al., 2001).
Fish. Boiling ten species of fish failed to eliminate allergenicity in DBPCFC (Bernhisel-Bradbent et al., 1992b). IgE binding to fish proteins in immunoblots was reduced, but not eliminated. Canning (presumably due to the heat processing) appears to reduce allergic reactions to tuna and salmon in allergic patients tested by DBPCFC (Bernhisel-Broadbent et al., 1992b). IgE binding of allergenic proteins from canned fish was reduced by 98 to 99% compared to boiled fish. IgE binding studies indicate that fish allergens are present in surimi (Mata et al, 1994).
Shellfish. Boiling does not reduce the allergenicity of shrimp allergens (Daul et al., 1988; Naqpal et al., 1989).
Soy. Heating soybeans at 100°C for 60 minutes does not completely eliminate IgE binding to allergenic soy proteins (Burks et al., 1992). Various soybean products including sprouts, soy sauce, hydrolyzed soy protein tofu, miso, and lecithin all retained IgE-binding activity (Besler et al., 2001). IgE binding proteins have been found in soy lecithin (Gu et al., 2001; Porras et al., 1985; Paschke et al., 2001). Allergic reactions to soy lecithin have also been reported (Renaud, 1996; Palm, 1999). The protein content of soy lecithin has been reported to vary between 2.8-202 mg per 100 g (Besler et al., 2001; Paschke et al., 2001). IgE binding proteins have been consistently detected in unrefined soybean oils (Paschke et. al., 2001), but inconsistently in refined oil (Awazuhara et al., 1998; Paschke et al., Errahali et al., 2002)
Tree nuts. Protein extracts of several hazelnut-containing products demonstrated less IgE binding than raw hazelnut aqueous extracts suggesting that heating reduced allergenicity. However, some IgE binding capacity remained (Wigotzki et al., 2001). Several cases of anaphylaxis have been described for a variety of processed nut-containing products, suggesting that tree nuts in general retain allergenic activity after heating (Besler et al., 2001).Roasting, blanching, autoclaving, or microwaving did not change the ability of animal antisera to bind almond proteins (Venkatachalam et al., 2002).
Wheat. Baking of wheat flour-containing foods results in the loss of IgE binding to one group of recognized wheat allergens, the alpha-amylase inhibitors. However, baking does not affect the ability of wheat prolamins to bind IgE from wheat allergic individuals (Simonatoet al. 2001). The wheat allergen omega-5 gliadin also retains allergenic activity after cooking. For example, Daengsuwan et al. (2005) found IgE to omega-5 gliadin in seven children who had anaphylactic reactions to breads, buns, noodles, macaroni and pizza."
