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1 Division for Food Science and Technology, Council for Scientific and Industrial Research, P.O.
Box 339, 0001 Pretoria, RSA
2 Department of Viticulture and Enology, University of
California, Davis, CA 95616-5270.
Grenache free-run juice was treated with pectinase to hydrolyze caftaric acid to caffeic acid and fermented as
for white wine. To increase the rate, oxidation of the wine was carried out at pH 7.0 in 100% oxygen at 20°C.
Samples were analyzed by reversed-phase HPLC with diode array uv-visible detection at 200 nm and peak
scanning from 200 to 400 nm. Caffeic acid in the wine and in the model solutions (as controls) was oxidized,
respectively, at first order rate constants 2100 and 2200 x 10-5 per hour. Similar products were observed in
both systems by retention time and comparison of uv-visible spectra. Browning occurred at a faster rate in the
model solution with ethanol than in the wine (3900 and 2100 x 10-5 per hour, respectively). In all instances, the
brown color formed correlated well with caffeic acid consumed by oxidation (p 
0.01; r 0.959; n = 5).
Key words: caffeic acid, chlorogenic acid, caftaric acid, autoxidation, browning, HPLC
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