Curcumin is a natural antioxidant with strong biological and chemical activity. The curcumin degradation was carried out under weak alkaline conditions at room temperature, integrated used by means of column chromatography, UV, IR, NMR, MS and other spectral analysis techniques, the chemical structure of the major degradation products was isolated and identified. For the reaction process, the qualitative and quantitative studies were carried out from two aspects: substrate elimination and product formation by HPLC-DAD spectroscopy analysis technology. Ascorbic acid was used as a positive control, and its antioxidant activities were evaluated in vitro, by 1,1-diphenl-2-picrylhyrazyl free radical(DPPH·), hydroxyl radical(·OH) and superoxide radical() scavenging assays, and compared with curcumin quantitatively. The results showed that the main degradation of curcumin at room temperature under weak alkaline conditions was autoxidation reaction, both of which conformed to the first order kinetics. the structure of heptadiene -3,5-diketone in curcumin[(1E,6E)-1,7-bis-(4-hydroxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione] forms a quinone methide intermediate in the presence of alkaline environment, after a series of oxygenation, hydration, dehydration and rearrangement, the target compounds bicyclopentadiones was a cyclization product with a tetrahydrofuran ring and cyclopentanedione structure in the molecule, we named CURC[6-hydroxy-1-(4-hydroxy-3-methoxyphenoxy)-3-(4- hydroxy-3-methoxyphenyl)-1,3,3a,6a-tetrahydro-4H-cyclopenta[c]furan-4-one]. Based on the established stable and reliable spectrophotometric system, the results of in vitro free radical scavenging activity of CURC and curcumin are as follows. CURC has a certain scavenging activity on DPPH·, ·OH and , but the action intensity is significantly lower than that of curcumin. The EC50 values were 0.17 mmol/L and 0.022 mmol/L in the DPPH assay, 0.33 mmol/L and 0.098 mmol/L in the ·OH assay as well as 0.38 mmol/L and 0.056 mmol/L in the assay, respectively. The obtained results suggest that the pH condition should be strictly controlled during the application of curcumin and avoid the autoxidation reaction.
