Kinetics of Alkaline Degradation of the Food Pigments Curcumin and Curcuminoids

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.

Evaluation of chitosan microparticles containing curcumin and crosslinked with sodium tripolyphosphate produced by spray drying

“…Curcumin application in aqueous solution is limited to the basic pH range. 9,10 Curcumin solubility can be increased by chemical modification or derivatization, such as complexation or interaction with macromolecules, surfactants and copolymers. 11 The spray drying technique represents a good alternative to obtain a soluble system for the industrial application of curcumin.…”

Curcumin: From ancient medicine to current clinical trials

“…Another study found pseudo-zero-order kinetics of curcumin decomposition when working in unbuffered aqueous medium of pH 10 -13.5, with a rate constant of 1.39 10 -9 M/min [150]. A recent study showed firstorder kinetics of degradation for curcumins I, II and III, where phosphate, borate, Tris and carbonate buffers were employed [153]. Curcumin III (bisdemethoxycurcumin) was the most stable, with a rate order of I > II > III.…”

Food colourants

“…146 Whilst HPLC is the most common technique used for the determination of curcumin, the separation and individual quantitation of the three curcuminoids is important because their extinction coeffi cients and stabilities vary. [147][148][149] Additionally, when used in combination with annatto, the isomers of the yellow-coloured thermal degradation products of annatto exhibit similar chromatographic behaviour to the curcuminoids. Since the curcuminoids are not currently readily available as pure reference materials they normally require preparation from turmeric extracts, which is very time consuming.…”