Heating induces chemical modification and variable solubility of pecan allergens

Authors: DUPRE, REBECCA - Oak Ridge Institute For Science And Education (ORISE); PATIL, SHAINA - Former ARS Employee; Lloyd, Steven; GRIMM, CASEY - Former ARS Employee; Smith, Brennan; Mattison, Chris

Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/26/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: Tens of millions of Americans have food allergies, and the occurrence of food allergy appears to be increasing. Food allergy reactions are mediated by a specific type of antibody called immunoglobulin-E (IgE). When IgE binds to allergens it can cause very severe reactions. Pecan nuts are a common cause of food allergy and reactions to pecan nuts can be severe. Cooking can alter the properties of food allergens and reduce or enhance their ability to cause allergic reactions. Pecan nuts contain three proteins that commonly acts as allergens, including Car i 1, Car i 2, and Car i 4. We show that heating pecan nuts can drastically alter the solubility of the Car i 2 and Car i 4 pecan nut allergens. Conversely, heating pecan nuts can increase the relative proportion of the Car i 1 allergen released in soluble pecan nut extracts. We have identified several specific heating-induced modifications on the Car i 1, Car i 2, and Car i 4 allergens. Some of these modifications lie within allergen sequences shown to interact with IgE. These changes in solubility and the heating-induced modifications may affect how these allergens interact with IgE antibodies. Continued research on the pecan allergen modifications identified here, combined with clinical testing, will clarify the role thermal processing has in affecting the detection of allergens in foods and how they contribute to allergic reactions.

Technical Abstract: Approximately 32 million Americans have food allergies, and the incidence of food allergy appears to be increasing. Food allergy reactions are mediated by immunoglobulin-E (IgE) binding to allergens. Pecan nuts contain three conserved seed storage proteins (termed Car i 1, 2, and 4) that commonly act as allergens. Heating can increase the aromatic and sensory qualities associated with pecans. Heating pecans also alters allergen solubility and induce chemical modification of allergen amino acids. To characterize changes in solubility, chemical modification, and antibody binding to proteins pecan nuts were heated at 300'F for 12, 20, and 24 minutes and extracts were analyzed. Gel electrophoresis and protein staining indicated the aqueous solubility of the Car i 2 and Car i 4 allergens had an inverse relationship to the length of heating, while the solubility of the Car i 1 allergen remained relatively constant. Similarly, western blotting with an anti-pecan polyclonal sera indicated recognition of both Car i 2 and Car i 4 was decreased following heating, while Car i 1 binding was relatively unchanged. Mass spectrometric analysis of pecan extracts showed little change in the observed Car i 1 peptides during heating, while there were variations in the most frequently observed tryptic peptides from Car i 2 and Car i 4 as a function of heating. Heat-induced lysine residue modifications, including carboxymethyl, carboxyethyl, and hydroxymethylOP moieties, were identified in all three pecan allergens by mass-spectrometry. In some cases, these modifications were found to lie within or proximal to mapped IgE binding sites and would be expected to prevent digestion by trypsin. The results indicate that changes in pecan allergen solubility and the occurrence of chemical modification after heating could hinder the detection of allergens in foods and modify their potency as allergens.