Detection of Turmeric in Foods by Rapid Fluorometric Method and by Improved Spot Test

Abstract

Abstract The rapid test for turmeric is based on the fluorescence of curcumin, the principal pigment of turmeric. In a water-saturated n-butanol solution, its excitation maximum is 435 nm and the emission maximum is 520 nm. In the test described, which was applied to pickles, salad dressings, and baked goods, a sample is shaken with the butanol solvent and the filtered extract is scanned for a 520 nm peak on a spectrophotofluorometer that has been adjusted to give 100% scale deflection for a standard curcumin solution. Extracts of pickles and salad dressings are scanned directly. Extracts of enriched baked goods are treated to remove riboflavin fluorescence by partitioning both riboflavin and curcumin from butanol into a solution of 0.1N NaOH-15% NaCl, acidifying the latter with CH3COOH, reducing the riboflavin with Na2S2O4, and reextracting curcumin from acid solution into butanol for fluorometric scanning. No interference is caused by annatto, carotene, tartrazine, or egg yolk solids. A spot test may be performed on the butanol extract. The solution is evaporated to dryness, the residue is dissolved in a few drops of ethanol, and the spot test is performed with a boric acid reagent of considerably improved sensitivity.