Extraction, purification and stability of the pigment of chestnut shells

Extraction, purification process and stability of the pigment of chestnut shells were explored. The results showed that this pigment dissolved easily in alkaline solution, but undissolved in noapolar solvent. This pigment was extracted with 1%NaOH, then was extracted for 3 times with petroleum ether and ethyl acetate. TLC indicated that high purity of pigment could be obtained with ethanol-precipitation, acid-precipitation and recrystallization method. The UV spectrum of the pigment showed that there were two apparent absorption peaks at 223nm and 264 nm in distilled water, and at 218 nm and 264 nm in methanol, which suggested that benzene rings and phenol hydroxyl existed in the chemical structure of the pigment. The absorption at 264 nm of the pigment was sensitive to pH value. The absorption at 510 nm of the pigment increased gradually with pH value from 2.0 to 6.0, but changed little with pH value from 8.0 to 14.0. Quantitative determination of the pigment could be conducted by the optical density at 510 nm when pH was 10.0; the pigment could be precipitated by many metal ions, but relatively stable for light, temperature, oxidants and reducing agents.