Kinetics of Alkaline Degradation of the Food Pigments Curcumin and Curcuminoids
Manuscript No. 96056 of the Arkansas Agricultural Experiment Station, Fayetteville, AR.
We gratefully acknowledge Kalsec, Inc. (Kalamazoo, MI) for providing samples of purified curcumin, demethoxycurcumin and bis-demethoxycurcumin and turmeric oleoresin. Special appreciation is acknowledged for technical advice provided by Dr. Ed Claussen, Dept. of Chemical Engineering, U. of Arkansas.
ABSTRACT
Alkaline degradation of the pigments curcumin (CC), demethoxycurcumin (DMC) and bis-demethoxycurcumin (BDMC) in aqueous solutions of purified and commercial oleoresin sources was investigated. Alkaline degradation of the compounds corresponded to pseudo-first-order kinetics. Responses were similar for pigments combined or alone in solutions. Profiles of rate constants were closely associated to polynominal curves. Degradation rate constants rapidly increased from pH 7.45 to a maximum at about 10.2 and then tended to decline at higher pH. Rates of alkaline degradation were lower for BDMC than for CC and DMC. Halflives of CC, DMC and BDMC at pH 7.45 were 900, 1700 and 2200 hr, respectively. In contrast, half-lives of CC, DMC and BDMC at pH 10.2 were 0.4, 1.0 and 5.0 hr, respectively. Use of BDMC instead of CC in alkaline foods would be expected to improve color stability.
