Curcuminoids antioxidative activity

Antioxidant capacities of common individual curcuminoids were determined in vitro by phosphomolybdenum and linoleic acid peroxidation methods. Antioxidant capacities expressed as ascorbic acid equivalents (pmol/g) were 3099 for curcumin, 2833 for demethoxycurcumin, and 2677 for bisdemethoxycurcumin at concentrations of 50 ppm. The same order of antioxidant activity (curcumin > demethoxycurcumin > bisdemethoxycurcumin) was observed when compared with BHT (buty-lated hydroxyl toluene) in linoleic peroxidation tests. The antioxidant activity of curcumin in the presence of ethyl linoleate was demonstrated and six reaction products were identified and structurally characterized. The mechanism proposed for this activity consisted of an oxidative coupling reaction at the 3 position of the curcumin with the lipid and a subsequent intramolecular Diels-Alder reaction. ... 

Ruby, A.J., Kuttan, G., Dinesh Babu, K., Rajasekharan, K.N. and Kuttan, R. (1995) Antitumor and antioxidant activity of natural curcuminoids (Curcuma longa) on iron-induced lipid peroxidation in the rat liver. Food and Chemical Toxicology 32, 279-283. 

From the rhizomes of C. longa, several curcuminoids (237-240) [191], (245,246) [192] and two curcumin related phenolic compounds (247,248) [191] were isolated. Antioxidant activity of the two phenolic compounds 247 and 248 was determined by inhibiting the autooxidation of linoleic acid and comparing the activity with that of curcumin [191]. Compounds 247 and 248 showed stronger activity than that of curcumin. It seems to indicate that the chelation of the 1,3-diketone moiety is not so important... 

Further studies are required to unravel this mystery of how the methoxy substitutions and the a, p-unsaturated p-diketone moiety actually influence conformational changes, lipophillicity, electron density distribution, and redox properties of curcuminoids. Correlating these physicochemical properties with the unique pleiotropic effects of curcuminoids is a rewarding exercise. Such studies would definitely provide proper reasoning in understanding these markedly different antioxidant, antitumor, and anti-inflammatory activities of natural curcuminoids from turmeric. 

Masuda T., Jitoe A. Antioxidative and antiinflamatory compounds from tropical gingers isolation, structure determination, and activities of cassumunins A, B, and C, new complex curcuminoids from Zingiber cassumunar. Journal of Agricultural and Food Chemistry, 42 1850-1856 (1994). 

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