A Simple Method for Confirmation of Amaranth, Cochineal Pigment and Laccaic Acid by Cellulose Acetate Membrane Electrophoresis

Abstract

Recently, the addition of natural colors has been increasing instead of artificial dyes in commercial food. In the qualitative tests of tar dyes, we used the wollen yarn staining method for the clean up of dyes. By this method, carminic acid, the pigment of cochineal and laccaic acid, coloring matter in resin known as stick lac, produced by lac insect, is caught together with acid tar dyes. In the paper chromatographic identification of the dyes, doubtful spots were shown by the above-mentioned dyes in the chromatogram for amaranth when the solvent system of isoamylalcohol: acetone: water (5: 6: 5, v/v/v) was used. Further, when solvent systems were used, it was difficult to identify which color stuff was laccaic acid or carminic acid because they were mixtures of pigments having analogous chemical structures but different Rf values.Amaranth has three sulfonyl moieties in the molecule, laccaic acid has two carboxyls while carminic acid has one carboxyl. Therefore, electrophoretic analysis might be useful in the separation of these three color stuffs on a standpoint of negative charge in their molecules. Thus, we attempted the separation and identification of them by cellulose acetate membrane electrophoresis.Using M/15 phosphate buffer (pH 7.0, ionic strength 0.147) as electrolyte, electrophoresis was conducted for 20 minutes at a constant current of 0.6mA/cm across membrane. The running zones of pigments moved all to the anode, and separation was complete, with the degree of mobility in the order of amaranth, laccaic acid and carminic acid.