The stability to light of cyanidin-3-glucosyl arabinoside in DMSO and in water, in acid solutions with or without complexation with tannic acid was determined by measuring the decrease of the absorbance of the solutions. The values for the apparent first-order reaction rate constant and t1 2 were calculated. The hypochromic effect observed in DMSO solutions when tannic acid was added as a co-pigment prevented the calculation of the complexation constant (K) for the anthocyanin-tannic acid, indicating that the predominating form in this system is the AH+. Although loss of absorbance was considerably faster in DMSO than in water under the same conditions, tannic acid effectively retarded discoloration in both DMSO and water. © 1994.512183185Adams, Thermal degradation of anthocyanins with particular reference to the 3-glicosides of cyanidin I in acidified aqueous solutions at 100°C (1973) Journal of the Science of Food and Agriculture, 24, pp. 747-762Asen, Stewart, Norris, Copigmentation of anthocyanins in plant tissues and its effect on color (1972) Phytochemistry, 2, pp. 1139-1144Bobbio, Bobbio, Stringheta, Stability of copigmented anthocyanins from Panicum melinis toward light and oxygen at different pH (1992) Proceedings of the XVI Internat. Conference—Groupe Polyphenols (JIEP), Vol. 16(1), pp. 241-244. , D.T.A, FranceBrouillard, (1982) Anthocyanins as Food Colors, , P. Markakis, Academic Press, N. Y., U.S.ABrouillard, Iacobucci, Sweeny, Chemistry of anthocyanin pigments (1982) UV-VIS spectrophotometric determination of the acidity constants of apigenidin and 3 related 3-deoxyflavilium salts, 104, pp. 7585-7590. , J.ACSBrouillard, Mazza, Saad, Albrecht-Gary, Cheminat, The copigmentation of anthocyanins—a microprobe for the structural study of aqueous solutions (1989) J. ACS, 111, pp. 2604-2610Brouillard, Wigand, Dangles, Cheminat, pH and solvent effects on the copigmentation reaction of malvin with polyphenols purine and pyrimidine derivatives (1991) Journal of the Chemical Society, Perkin Transactions 2, 2, pp. 1235-1241Dangles, Brouillard, A spectroscopic method based on the anthocyanin copigmentation interactions and applied to the quantitative study of molecular complexes (1992) Journal of the Chemical Society, Perkin Transactions 2, 2, pp. 247-257Francis, (1982) Anthocyanins as Food Colors, , P. Markakis, Academic Press, N.Y, Chapter 7Maccarone, Macarrone, Rapisarda, Colour stabilization of orange fruit juice by tannic acid (1987) International Journal of Food Science & Technology, 22, pp. 159-162Mazza, Brouillard, The mechanism of co-pig-mentation of anthocyanins in aqueous solutions (1990) Phytochemistry, 29, pp. 1097-1102