Analysis of Polyphenols in Foods
Phenolic compounds in food and nutraceuticals originate from plant sources (van Sumere 1989; Shahidi 2000, 2002; Shahidi and Naczk 2004). Their occurrence in animal tissues and nonplant materials is generally due to the ingestion of plant foods. Plants and foods contain a large variety of phenolic derivatives, including simple phenols, phenylpropanoids, benzoic acid derivatives, ¯avonoids, stilbenes, tannins, lignans, and lignins. These rather varied substances are essential for the growth and reproduction of plants and also act as antifeedants and antipathogens (Butler 1992). The contribution of phenolics to the pigmentation of plant foods is also well recognized. In addition, phenolics function as antibiotics, natural pesticides, signaling substances for establishing symbiosis with rhizobia, attractants for pollinators, protective agents against ultraviolet (UV) light, insulating materials to make cell walls impermeable to gas and water, and structural materials to give plants stability.