Analysis of lac and cochineal colors in foods using reversed-phase thin-layer chromatography/scanning densitometry

A technique for the analysis of lac and cochineal colors using reversed-phase TLC and scanning densitometry is described. The technique involves the following three steps: 1) clean-up of the colors with a C18 cartridge, 2) separation of the colors by reversed-phase C18-TLC using methanol-0.5mol/L oxalic acid (5.5:4.5) as a solvent system, and 3) measurement of visible absorption spectra of the colors using scanning densitometry without isolation of the colors. In order to investigate the capability of the present method, 122 commercial foods were analyzed, and their chromatographic behaviors and spectra were observed. The separation and the spectra obtained were not affected by coexisting substances in the foods and the spots always gave the same Rf values and spectra as the standards, with good reproducibility. The present method is considered to be useful for the rapid analysis of lac and cochineal colors in foods.