Physical stability of shikonin derivatives from the roots of Lithospermum erythrorhizon cultivated in Korea

Five red shikonin pigments, deoxyshikonin, shikonin, acetylshikonin, isobut ylshikonin, and beta-hydroxyisovalerylshikonin, were isolated from the root s of Lithospermum erythrorhizon cultivated in Korea. The purified pigments were red, purple, and blue at acidic, neutral, and alkaline pH values, resp ectively. Physical stability of the purified pigments against heat and ligh t in an aqueous solution was examined for possible value-added food coloran ts. The thermal degradation reactions were carried out at pH 3.0 (50 mM gly cine buffer) in 50% EtOH/H2O. Deoxyshikonin (t(1/2) = 14.6 h, 60 degrees C) and isobutylshikinin (t(1/2) = 19.3 h, 60 degrees C) are relatively less s table than other shikonin derivatives (t(1/2) = 40-50 h, 60 degrees C). Act ivation energies of thermal degradation of the isolated pigments were calcu lated. The activation energy of deoxyshikonin was the highest (12.5 kcal mo l(-1)) and that of beta-hydroxyisovalerylshikonin was the lowest (1.71 kcal mol(-1)) value. Light stabilities of the pigments were similar to each oth er in that the half-life values of photodegradation for 20000 1x light inte nsity were 4.2-5.1 h.