Abstract: Pigment was extracted from Quercus variabilis acorn shell harvested from Qinba mountain area, China and it was qualitatively analyzed and structurally characterized by ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy. Meanwhile, the antioxidant activity was evaluated. The results showed that the pigment contained abundant polyphenols, with condensed tannins being the predominant species, accounting for up to about 89% of the total polyphenols. The UV-vis and FTIR analysis proved that the pigment molecule contained intramolecular hydrogen bonds as well as multiple benzene rings and phenolic hydroxyl groups. The pigment was easily soluble in ethanol, methanol, alkali solution and water, slightly soluble in ethyl acetate, and insoluble in benzene. The pigment exhibited good stability in acidic environments, but its color became darker with increasing pH in alkali environments. The pigment had good resistance to light and heat, and it was stable in K+, Ca2+ and Na+ solution and could basically retain its color although generating a precipitate in Al3+, Mg2+ and Zn2+ solution. The color of the pigment was obviously faded in antioxidant solution but was not changed in reducing agent solution. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging capacity and reducing power of the pigment were stronger than those of VC, while the superoxide anion scavenging capacity was slightly weaker than that of VC. Therefore, the pigment has a good antioxidant effect in vitro．

Key words: Quercus variabilis acorn shell, pigment, stability, antioxidant activity