Oxidation of gallotannins, ellagitannins and proanthocyanidins at high pH

CELL 21

Ann E. Hagerman, hagermae@muohio.edu1, Raymond V Barbehenn, rvb@umich.edu2, Christopher P. Jones2, and J P. Salminen3. (1) Department of Chemistry & Biochemistry, Miami University, Hughes Laboratory, Oxford, OH 45056, (2) Departments of Molecular,Cellular and Developmental Biology and Ecology and Evolutionary Biology, University of Michigan, MCDB & EEB, University of Michigan, Ann Arbor, MI 48109, (3) Department of Chemistry, University of Turku, Vatselankatu 2, Turku, 20014, Finland
In an attempt to understand reactivity of tannins in the highly basic conditions of the insect gastrointestinal tract, we compared the oxidation of hydrolyzable and condensed tannins at pH 10. We used electron paramagnetic resonance spectrometry to quantify semiquinone radicals in anoxic conditions, and we spectrophotometrically assessed the rate of nonenzymatic browning in solutions containing ambient oxygen concentrations. We compared a series of galloyl glucoses (mono- through pentagalloyl glucose); ellagitannins pedunculagin, oenothein B, cocciferin D2, vescalagin, and castavloninic acid; and proanthocyanidin monomers through polymers. Ellagitannins were most easily oxidized, forming high concentrations of semiquinone radicals and browning at the highest rates. On average, galloyl glucoses and high molecular weight gallotannins had intermediate to low reactivities. Condensed tannins generally formed low levels of semiquinone radicals and browned most slowly among the tannins tested.
 

Poster Session
4:00 PM-6:00 PM, Sunday, 10 September 2006 Moscone Center -- Hall D, Poster

Division of Cellulose & Renewable Materials

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006