Free radical scavenging activity determination and quantitative analysis of curcuminoids in Curcuma zedoaria rhizome extracts by HPLC method

Abstract

Curcuma zedoaria (Zingiberaceae) is a medicinal plant containing antioxidant and anti-inflammatory curcuminoids similar to the well-known Curcuma longa. So far, the content of each curcuminoid in the rhizome extract of C. zedoaria in Thailand has not been reported. A high-performance liquid chromatography (HPLC) method was developed and validated for quantitative analysis of curcuminoids (curcumin, demethoxycurcumin and bisdemethoxycurcumin) content in 70% ethanolic extracts of the rhizomes of C. zedoaria collected from 10 different locations in Thailand. The method demonstrated good linearity, precision and accuracy. The content of curcumin in all crude extracts was found in the range of 1.46 ± 0.45 to 5.73 ± 0.11 %w/w (average 2.73 ± 1.24 %w/w) whereas the contents of demethoxycurcumin, which is a major component, and of bisdemethoxycurcumin were in the ranges of 3.15 ± 0.15 to 10.98 ± 0.28 %w/w (average 7.37 ± 2.71 %w/w) and 0.49 ± 0.02-2.99 ± 0.20 %w/w (average 1.40 ± 0.82 %w/w) respectively. The highest average total curcuminoids content in the crude extracts was 16.83 ± 0.62 %w/w whereas the lowest content was 6.09 ± 1.79 %w/w. This information will be useful as a guidance for further standardization of C. zedoaria raw material and extracts. Free radical scavenging activity of all extracts was determined using 1,1-diphenyl-2-picrylhydrazyl scavenging assay. Values of EC50 of all extracts were found in the range of 18.29 ± 0.05 to 40.33 ± 2.24 μg/ml (average 25.71 ± 7.54 μg/ml). Free radical scavenging activity of the separated pure compounds was found in descending order of curcumin > demethoxycurcumin > bisdemethoxycurcumin.