High Quality Content by WIKIPEDIA articles! A polyphenol antioxidant is a type of antioxidant containing a polyphenolic or natural phenol substructure. Numbering over 4,000 distinct species, many of these compounds have antioxidant activity in vitro but are unlikely to have antioxidant roles in vivo. Rather, they may affect cell-to-cell signaling, receptor sensitivity, inflammatory enzyme activity or gene regulation.