Polyphenols in foods: Classification, methods of identification, and nutritional aspects in human health

Polyphenols widely exists in various foods, including main crops, fruits, beverages and some wines. Famous representatives of polyphenols, such as resveratrol in red wine, (−)-epigallocatechin gallate in green tea, chlorogenic acid in coffee, anthocyanins in colored fruits, procyanidins in grape seed have become hot research topics in food science and nutrition. There have been thousands of papers on the biochemistry, chemistry, nutritional values and population-based investigations of dietary polyphenols. In this chapter, we reviewed the published articles and database of dietary polyphenols to draw a profile for the classification, structural identification, and biological activities mainly based on enzymes, cell bioassay and animal models, as well as the population-based investigation results. The typical compound and its health benefits for each category of polyphenols was also introduced. The identification of dietary polyphenols could be solved by combined spectroscopy methods, of which the liquid chromatography tandem mass spectrometry is highlighted to greatly increase the efficiency on structural identification. Although the population-based investigation showed some controversial results for health benefits, the multi-functions of dietary polyphenols on preventing metabolic syndromes, various cancers and neurodegenerative disease have attracted much attention.