Detection method of madder color, cochineal extract, lac color, carthamus yellow and carthamus red in processed foods by TLC

Abstract

Thin-layer chromatography (TLC) methods were developed to detect five kinds of natural colors in processed foods. Cochineal extract, lac color and carthamus yellow were extracted from samples with 50% aqueous methanol or 50% aqueous acetonitrile under an acidic condition, and these extracts were purified using a polyamide column with 2% aqueous ammonia-ethanol (1:1) solution as the eluant. Madder color and carthamus red were extracted from samples with 50% aqueous N, N-dimethylformamide or 50% aqueous acetonitrile, and these extracts were purified using a reversed-phase column (C18) with 50% aqueous methanol as the eluant. The natural colors in each eluate were detected by C18 reversed-phase and cellulose high performance TLC. For liquid processed foods, the extraction was not necessary. Commercial food additive grade natural colors were used as standards for TLC.The detection limits from spiked processed foods were 100ppm for madder color, 5ppm for cochineal extract and lac color, 30-50ppm for carthamus yellow and 5-25ppm for carthamus red.The proposed method was successfully applied to the detection of natural colors in 30 kinds of commercial processed foods whose labels indicated them to contain natural color.