Effect of Copigmentation on Thermal Stability of Hibiscus sabdariffa anthocyanins

Abstract

Synthetic food colors are widely used in foodstuffs to increase consumer acceptance. The use of non permitted colors or overindulgence of permitted colors reported to have toxicity in humans. For substitution, study of natural colorants is becoming an immense area of research. Natural coloring compounds are water soluble anthocyanins, betalains, carminic acid, and the oil soluble carotenoids and chlorophylls. Anthocyanins are bluepurple-red-orange colored plant flavonoids. So far, anthocyanins have not been broadly used in foods and beverages, since they are not as stable as synthetic colors. Copigments are colorless compounds forming intermolecular complex with anthocyanins to present far greater color than natural anthhocyanins thus preventing formation of colorless pseudobase and increases its stability. Purified anthocyanin solutions were copigmented with phenolic acids like gallic acid, tannic acid, ferulic acid and ellagic acids and with flavonoids like rutin and quercetin in different concentrations between anthocyanins and copigments viz. 1: 0, 1: 2, 1: 4, 1: 6 at pH values (1.5, 2.5, 3.5, 4.5). Copigmentation was observed using UV-visible spectrophotometry. The maximum effect, revealed by hyperchromic shift was observed at all pH values. Ferulic acid was effectual copigment causing hyperchromic and bathochromic shifts in absorption. Copigmention studies of Hibiscus sabdariffa anthocyanin extract with ferulic acid in 1: 6 concentration at acidic pH (pH 2.5) remarkably improved heat stability of Hibiscus sabdariffa anthocyanins.