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Fields of Expertise: Polyphenol analytics; Food processing; Mass spectrometry; Bioactivity; Coffee; Cocoa; Tea

Author details: Nikolai Kuhnert is a group leader at the Analytical Chemistry Research Group at Jacobs University Bremen in Germany. He obtained his Ph.D. in 1995 at the Universität Würzburg. Following postdoctoral years at Cambridge and Oxford, he started his own independent research career at the University of Surrey. In 2006, he accepted a position at Jacobs University Bremen, where he is currently a full Professor of Analytical Chemistry.  His research interests cover modern mass spectrometry and its application to the characterization of processed food. Using both high-resolution and tandem MS strategies he contributed to a detailed understanding of products such as roasted coffee, cocoa and black tea. Next to the chemistry underlyiMass ng food processing a focus is placed on the biological activity of polyphenols with a special emphasis on antimicrobial activity. Prof. Kuhnert is the author of some 200 peer-reviewed publications, with an h-index of 50, and has been cited over 10 000 times.

Abstract: Polyphenols possess a high inherent chemical reactivity. As electron-rich aromatic compounds, they are excellent nucleophiles and prône to oxidation reversing their reactivity to yield electrophilic quinoid species. In food processing using enzymatic or thermal chemical reactions a small number of genuine secondary plant metabolites are converted into thousands at times tens of thousand reaction products. On human consumption, our gut microbiota and subsequently after absorption hepatic enzymes further convert highly reactive polyphenols to novel structures. The great Edwin Haslam termed such compounds « Children of Nature » indicating their relationship to Natural Products. In the contribution, we will review mass spectrometry-based strategies developed to investigate such highly complex mixtures of polyphenols arising from food processing. As examples, we will discuss briefly the chemistry of coffee roasting and thearubigin formation in black tea fermentation, including aspects of their human metabolism. Mass spectrometric techniques are based on ultra-high resolution mass spectrometry as well as on tandem mass spectrometry, allowing at times unambiguous structure elucidation and more commonly structure hypothesis generation. Finally, biological consequences and consequences for polyphenol valorization are discussed.