Figure 1.

Classification of monomeric polyphenolic compounds according to Zhang et al. 2016 [2], with some modifications. Polyphenols are plant-derived compounds of four main structural subclasses: Phenolic acids, stilbenoids, flavonoids, and lignans. Phenolic acids are derivatives of benzoic or cinnamic acids (i.e., caffeic acid). Stilbenoids are hydroxylated stilbene derivatives (i.e., resveratrol). Lignans are diphenolic compounds (i.e., lariciresinol). Flavonoids are phenylchromone derivatives, which are subgrouped into flavanones, flavonols, flavanols, flavones, isoflavones, and others (anthocyanidins, chalcones, and neoflavonoids). Some authors classify phenolic amides (i.e., capsaicin) and ellagic acid derivatives [3] as additional polyphenol groups.