Separation and free radical‐scavenging activity of major curcuminoids of <i>Curcuma longa</i> using HPTLC‐DPPH method

A direct HPTLC assay was developed for the determination of total curcuminoids and three individual curcuminoids, curcumin, demethoxycurcumin and bisdemethoxycurcumin. In addition, a new procedure was developed to separate and quantitative the free radical-scavenging activity of individual compounds from the rhizome of Curcuma longa L. (Zingiberaceae) based on the combination of HPTLC with a diode array detector (DAD) and post chromatographic DPPH(*) radical derivatisation. It was established that both individual curcuminoids and the extract of C. longa were capable of scavenging DPPH(*) radicals. From the estimated ID(50) values, it can be seen that the order of activity was curcumin > demethoxycurcumin > bisdemethoxycurcumin >> ascorbic acid. However, the ID(50) values of curcuminoids were not significantly different. The data indicates the presence of a synergistic mechanism of antiradical activity of curcuminoids.