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Gliadins, the major proteins of the wheat flour, are a family of monomeric and disulphide‐bonded proteins formed by a non‐repetitive domain rich in α‐helix structures and heterogeneous repetitive domains rich in β‐reverse turns. Gliadins may be strong food allergens, and many studies have explored the mechanisms of gluten allergenicity, with the final aim to properly modify gluten proteins in order to decrease allergen immunoreactivity. In the present study, Raman spectroscopy was used to gain more insights into the conformational changes of gliadins upon interaction with different anthocyanins (kuromanin, callistephin, oenin, cyanin, pelargonin, malvin). Anthocyanins are powerful antioxidant molecules with anti‐carcinogenic properties and largely widespread natural colorants present in vegetables and flowers. Raman spectroscopy demonstrated that the anthocyanins under study induce in gliadins conformational changes of different extents. The treatment with malvin, kuromanin and callistephin induced significant changes in the tyrosine environment, while pelargonin, oenin and cyanin did not. The treatment with any of the anthocyanins altered the distribution of the disulphide conformations: the gauche‐gauche‐trans conformation increased at the expenses of the gauche‐gauche‐gauche conformation. Malvin and pelargonin provoked a significant decrease of the β‐turns content. Since both the latter structural elements have been related to gluten allergenicity, anthocyanins appeared interesting molecules, in the context of the attempts to modify gliadins with the aim to decrease allergen immunoreactivity. Copyright © 2013 John Wiley & Sons, Ltd.

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The reactions between strongly electron-rich aromatic substrates (1,3,5-tris(N,N-dialkylamino)benzenes, neutral carbon super nucleophiles) and diazonium salts produce moderately stable sigma complexes (Wheland complexes). The reactivity of Wheland complexes with electrophiles (other diazonium salts, or 4,7-dinitrobenzofuroxan) produces exchange reactions in the electrophilic part: the better electrophile replaces the less powerful electrophile. In the same way, in Wheland complexes with the 1,3,5-tris(morpholinyl)benzene, the 1,3,5-tris(piperidinyl)benzene replaces the less powerful nucleophile 1,3,5-tris(morpholinyl)benzene. Evidence is reported here indicating that for the title system the reaction of the attack of the electrophilic reagent producing Wheland complexes is a reversible process. The final products of the diazo-coupling reactions undergo a further attack of some diazonium salts. From the final products of the double diazo-coupling reactions (diazo compounds), we collected evidence that is a clear instance of complete reversibility of the diazo-coupling reaction.

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