Chapter 14 Antioxidant Activity of Tannins and Tannin- Protein Complexes: Assessment In Vitro and In Vivo Ken M. Riedl 1 , Stephane Carando 1 , Helaine M. Alessio 2 , Mark McCarthy 1 , and Ann E. Hagerman 1, * 1 Departments of Chemistry & Biochemistry and 2 Physical Education, Health and Sport Studies, Miami University, Oxford, OH 45056 zyxwvutsrqponm The common food constitutents known as tannins are high molecular weight phenolic compounds comprised of gallic acid esters or flavan-3-ol polymers. Although tannins exhibit antioxidant activity in simple chemical assays, previous studies have not established the nutritional relevance of this activity for tannins found in foods such as fruits, wine or tea. We have demonstrated that both hydrolysable and condensed tannins scavenge free radicals in a kinetically complex fashion involving both a fast and a slow scavenging step. Structure/activity studies for monomeric and polymeric phenolic compounds showed that 4 moles of radical were scavenged per ortho-substituted diphenol group. The fast scavenging reaction was inhibited by complexation of the tannin to protein, but the overall capacity of the tannin-protein complex for scavenging was similar to that of the free tannin. Protein-tannin complexes were converted to a refractory form during reaction with free radicals, presumably because of zyxwvutsrqponm 188 © 2002 American Chemical Society Downloaded by OHIO STATE UNIV LIBRARIES on February 3, 2015 | http://pubs.acs.org Publication Date: March 4, 2002 | doi: 10.1021/bk-2002-0807.ch014 In Free Radicals in Food; Morello, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2002.