Characterisation of polyphenol-protein interactions using the apple allergen Mal d 1 as an example

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Polyphenols (PP), hydrophilic secondary plant metabolites, are associated with a number health promoting effects e.g. cardioprotective effects. This conclusion from epidemiological studies has been investigated in vitro and by intervention studies for years. PP always occur in plants in combination with cell wall components, proteins and/ or lipids. How-ever, in order to reduce complexity, most studies are performed without or minimizing the influence of macromolecular matrix components, e.g. by the administration of juices. Nevertheless, the inter-action of PP with the matrix influences the stability, solubility and bioaccessibility of PP. In addition, PP are able to irreversibly alter protein structures. This might lead to a decreased nutritional value or, as initial studies on peanuts and apples indicate, a reduction of the allergenic potential of these foods. PP are characterized by a large structural diversity and, therefore, differ significantly in their chemical properties, which plays a decisive role for the interaction with macromolecular matrices. This structure-effect relationship has not yet been investigated comprehensively. Detailed knowledge of the stability of PP-matrix interaction in vivo and in vitro, as well as the relevant impact factors and reaction conditions, do not exist. In this project, PP-protein interactions are examined thoroughly using the apple allergen Mal d 1 as an example and selected PP found in apples. So far, no significant correlation has been found between the allergenicity of an apple variety and its Mal d 1 content. However, since the varieties described by allergy sufferers as well tolerated usually exhibit high PP contents, it is assumed that the interaction between PP and the Mal d1 plays an important role in reducing the allergenic poten-tial. The aim of this project is to investigate the impact of the PP structure on mechanism, strength and kinetics of the PP-Mal d 1 interaction. It is intended to determine specific differences among allergenic and hypoallergenic apple varieties e.g. the qualitative and quantitative PP composition, the activity of oxidizing enzymes as well as the concentration of endogenous oxidation inhibitors using standard methods. The interaction between isolated PP and r-Mal d 1 is studied in simplified model systems. The interaction of the oligomeric PP structures (formed when apples are cut) with Mal d 1 is also of interest.The effect of PP interaction on the Mal d 1 conformation, which is assumed to be an important criterion for the allergenic potential, and its stability under oral digestion conditions, are assessed by circular dichroism and FT-IR spectroscopy. The methods established in this context, investigating the PP-Mal d 1 interaction, are transferable to further PP-protein interactions.