Flavan-3-ol monomers, commonly named catechins, and their oligomers and polymers (i.e., proanthocyanidins and condensed tannins) are polyphenolic compounds widespread in edible plants. Several health bene‚ts such as antioxidant, cancer preventive, cardiopreventive, antimicrobial, antiviral, and neuroprotective agents have been reported for this polyphenol class (Scalbert 1991; Santos-Buelga and Scalbert 2000; Aron and Kennedy 2008; De Pascual-Teresa et al. 2010). They are important constituents of food for the majority of people around the world and may be highly concentrated in some plant tissues. For instance, catechins may account for more than 25% of the dry weight of tea leaves (Balentine et al. 1997). Catechins and proanthocyanidins are found in common foods such as fruits (apples, pears, plums, strawberry, kiwi, dates, many red fruits, etc.), cereals (sorghum, barley, etc.), seeds and nuts (beans, peas, almonds, etc.), spices, aromatic plants, and more scarcely in vegetables. Flavanols are also found in various foodstuffs of plant origin (wines, tea, ciders, beers, chocolates, jams, puree, etc.) (Gu et al. 2004). Noticeably, in these processed foods, catechins and proanthocyanidins are not only present in their native form, but they have sometimes undergone structural changes especially related to their susceptibility to oxidation with a signi‚cant impact on their properties. The most obvious example is probably that of black tea catechins that are enzymatically oxidized, forming thea‘avins and thearubigins responsible for the color of the infusions (Tanaka et al. 2010).