Characterization of polyphenol-protein reactions in model systems and foods

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Phenolic compounds are quality determining compounds in plant-derived foods and are widely used as functional food ingredients, owing to their supposed beneficial effects on human health. For this purpose they are extracted from various sources such as tea leaves, grape skins and seeds, apples, and even medicinal plants. Being deprived of their natural protecting matrices, the phenolics are exposed to oxygen during processing and may therefore be oxidized to instable, reactive intermediates. These so-called quinones can interact with a number of food constituents, in particular with proteins. The technological and biochemical consequences of such reactions are manifold, e.g. crosslinking of proteins, changes in enzyme activities, reduced bioavailability of both amino acids and phenolics, and modifications of the immunological properties of food proteins. While it is the primary aim of this project to characterize the products formed by the reaction of phenolic compounds and proteins using highly sophisticated analytical techniques, a better understanding of the stability of phenolic compounds and their interactions with other food constituents would allow conclusions on the optimization of processes for the production of (functional) foods and would also, to a certain extent, allow the estimation of potential adverse effects. In view of the growing importance of functional foods within the overall food market, investigations into the reactivity of their bioactive constituents are essential. Knowledge of the alterations of proteins by reaction with phenolics may also lead to the production of hypoallergenic food. Thus, it is anticipated that the results of the proposed investigations will stimulate cross-disciplinary research, in particular in the fields of food chemistry and food technology, nutritional science, toxicology, and immunology.