Free Radical-Scavenging Activity of Phenolics by Reversed-Phase TLC

摘要

A method was developed to measure the radical-scavenging activity of compounds separated by reversed-phase TLC (RP-TLC) using phenolic acids as model analytes. TLC separation was followed by dipping the plate in a 0.04% (wt/vol) solution of 1,1-diphenyl-2-picrylhydrazyl (DPPH) in methanol. The compounds possessing radical-scavenging activity were detected as bright yellow bands against a purple background. A video documentation system based on a CCD video camera was used for the detection and quantification of the activity. The developed RP-TLC-DPPH method was compared to the widely used spectrophotometric DPPH assay. The results obtained by the two methods correlated well, apart from syringic acid, ascorbic acid, and n-propyl gallate, which proved to be outliers in the regresson analyses. The correlation coefficient, after ex-cluding outliers, was r~2=0.923. The RP-TLC-DPPH method was applied for the measurement of free radical-scavenging activity of rapeseed meal fractions. A total of 10 separated zones with free radical-scavenging activity were detected, with R_f values rangeing from 0.04 to 0.85. The results show that the method can be used for the effective fractionation and analysis of potential antioxidative compounds in natural extracts.