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Author's details: Jean-Paul Vincken is chairholder of the Laboratory of Food Chemistry (FCH), at Wageningen University (WU), The Netherlands, since 2019. Prior to his current position, he was: PhD student at FCH working on enzymatic degradation of xyloglucans (1990-1993); Researcher at FCH working on pectin degadation (1993-1996); Postdoc at the Laboratory of Plant Breeding (PBR, also WU) working on genetic modification of starch (1996-1999); Assistant professor at FCH (0.5 fte) and PBR (0.5 fte) (2000-2005); Assistant / associate professor at FCH, where he founded a new research line on ‘Phytochemicals’ (2006-2019), aiming at analyzing and modifying phytochemicals present in agricultural (raw or waste) materials to enhance their (bio)functional properties (e.g. health-promoting effects, antimicrobial activity, colour, taste). He holds some 10 patents and is the (co)author of over 180 peer-reviewed publications, with an h-index of 44, and has been cited over 6,500 times.

Fields of Expertise: Phytochemistry; Oxidation of phenolics; Prenylation of phenolics; Induction of prenylated phenolics by germination under stress; Enzymatic browning; Bitterness of phenolics; Estrogenic activity of isoflavonoids; Antimicrobial activity; Glucosinolates/isothiocyanates; Saponins; Intestinal conversions of phenolics; Food analysis (LC, MS); Plant cell wall chemistry/biochemistry.

Abstract: Enzymatic browning, catalyzed by polyphenol oxidase (PPO) is a well-known phenomenon upon processing of plant materials. In recent years, with the transition from animal-based to more plant-based proteins, it has gained relevance as oxidation of phenolics by PPO might also affect protein functionality besides discoloration of the protein isolates. In addition to enzymatic oxidation, also autoxidation of phenolics (i.e. in ready-to-drink green teas) and complexation of phenolics by metal ions (i.e. upon iron-fortification of foods) can occur, both leading to undesirable colors in food products. Nevertheless, there are also examples indicating that oxidation of phenolics in food materials is actually desirable. For instance, the conversion of monomeric green tea leaf catechins to dimeric (e.g. theaflavins) or oligomeric phenolics by PPO is responsible for the color of black tea. Other examples might be the oxidative coupling of phenylalkenoic acid amides to hordatines (barley) or avenanthramides (oat) by peroxidase. These oligomerized phenolics potentially have antimicrobial activity, and might be used as clean label food preservatives, once their potency as antimicrobials and toxicity profiles have been established. Finally, laccases can be used as valuable tools for oxidative degradation of lignin, which facilitates better utilization of plant biomass. The challenges in mitigating the undesirable oxidation reactions, and directing the desirable ones, are discussed against a backdrop of industrial applications.