An easy and fast test to compare total free radical scavenger capacity of foodstuffs

Abstract

An easy and fast test has been designed to compare the total free radical scavenging capacity (RSC) of various food samples. Black and green teas from different countries, and wines of different brands were studied and compared as examples of coloured liquids (water- and methanol-soluble); oils from different sources were used as examples of lipidic foodstuffs; apples of different varieties and spinach were analysed as solid foods. Dilutions of extracts of the described foodstuffs were prepared and aliquots of each dilution were spotted onto TLC silica gel layers in the form of a dot-blot test: layers were stained with a methanolic solution of the 2,2-diphenyl-1-picrylhydrazyl radical. Dots of extracts of foodstuffs with RSC turned yellow, with a colour intensity depending on the RSC compounds present in the dilutions. After 1 h staining, the intensity of the yellow colour was measured with a chromameter (b* parameter) at one of the dilutions at which the colour value was linearly correlated to the concentration of the sample. According to these readings the different samples were organised in decreasing order of b* values, an order which corresponded to the decreasing order of RSC as determined by spectrophotometric methods. The dot-blot test was sensitive enough to detect differences of RSC between varieties and brands of water- or methanol-soluble products, but was not adequate for lipid-based compounds. The test was also able to follow the variation of RSC during food processing as in, for example, the heat-treatment of spinach.