A REVERSED-PHASE TLC/SCANNING DENSITOMETRIC METHOD FOR THE ANALYSIS OF TOMATO, ORANGE, AND MARIGOLD COLORS IN FOOD

Abstract

ABSTRACT In the present study, a thin-layer chromatography (TLC) method for the analysis of tomato, orange, and marigold colors in foods was developed. The colors were extracted from food samples with ethyl ether, and after the extract was evaporated, the residue was dissolved in methanol. For the analysis of the tomato color, after the addition of water to the methanol solution, it was then purified through a C18 cartridge before being subjected to the TLC analysis. With respect to the analyses of the orange and marigold colors, after adding 2 mL of a 5% sodium hydroxide–methanol solution to the methanol solution, the mixture was occasionally stirred, kept away from light, and then allowed to stand for 24 hours at room temperature. Subsequently, the pH of the mixture was adjusted to 4.5 or less using 1 mol/L hydrochloric acid. The mixture was then purified through a C18 cartridge before being subjected to the TLC analysis. The TLC conditions were as follows: plate, RP-18F254S (Art. 15389, E. Merck); solvent system, acetonitrile–acetone–n-hexane (11 : 7 : 2) and acetone–water (9 : 1). The visible absorption spectra of the colors were measured using scanning densitometry without isolation of the colors. In order to investigate the capability of the present method, 95 commercial foods (33 for the tomato color, 38 for the orange color, and 24 for the marigold color) were analyzed, and their chromatographic behaviors and spectra were observed. The separation and obtained spectra were not affected by coexisting substances in the foods and the spots always gave the same Rf values and spectra as the standard with good reproducibility. The present method is considered to be useful for the rapid analysis of the tomato color, orange color, and marigold color in foods.