Chapter 23
Analysis of Curcuminoids by High-Performance Liquid Chromatography Thomas H. Cooper, Joseph G. Clark, and James A. Guzinski
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The effect of trace metal ions on the peak separation of curcuminoids using reverse phase HPLC has been demonstrated. At pH 3, using acetic acid buffer, severe peak tailing occurred after an amount of Fe(II) was added equal to 1000 times the background concentration found in the turmeric extract. The use of a citric acid buffer was found to be effective in separating curcuminoids without peak tailing. Calcium was found not to form a strong complex with curcumin under these conditions. Relative response factors for the three curcuminoids were found to be 1:1:1 at 422 nm.
The turmeric plant is used as a natural colorant in a variety of prepared foods. The yellow color it imparts is caused by curcumin (C) and its two related analogues, demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC) (Figure 1). In addition, antimutagenic and pharmaceutical applications have been found for curcuminoids and compounds made from curcuminoids (1-3).
Figure 1. Structures of curcumin, demethoxycurcumin and bisdemethoxycurcumin.
Chemistry Curcumin decomposes under alkaline conditions to ferulic acid and feruloylmethane (4,5). These researchers found that the rate constant for hydrolysis
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was pH-dependent and attributed this to various ionizable species existing in equilibrium in solution. This can also be inferred from the color changes from red to yellow to red as the pH is raised from 8. Because of these ionized species in solution, the presence of strong acids or bases can result in errors in the spectrophotometric analysis of curcuminoids. Therefore, a buffer is necessary for baseline separation of curcuminoids by reverse phase HPLC. Curcumin fades rapidly in solution (6). We have measured an approximately 5% decrease in absorbance during the time for typical sample preparation when clear rather than amber glassware is used.
Downloaded by UNIV LAVAL on May 8, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/bk-1994-0547.ch023
Coordination to Metals It is well known that curcumin will react with borate to produce a characteristic red complex (7-9). This is due to the keto-enol structure which is also capable of forming a six membered ring around metals such as iron(II), copper(II), and nickel(II) (10,11). Plants require small amounts of many metals for normal growth (72). In view of this, it is reasonable to expect that some of the total curcuminoids found in turmeric roots are actually coordinated with metals. In order to determine the approximate level of metal ion species in turmeric root, a sample from India was ground with a mortar and pestle and the curcuminoids extracted with acetone using a Soxhlet apparatus. Inductively Coupled Plasma emission spectroscopy was used to determine the concentrations of iron, calcium and magnesium. These results are shown in Table I. There is approximately a 10% weight yield of turmeric extract obtained from turmeric root. Thus, these results represent an extraction recovery of 0.91% for iron, 0.54% for calcium and 0.04% for magnesium. This would seem to indicate a strong iron and curcumin complex followed by much weaker Table I. Metal Ion Concentration complexes being formed with cal[Mg] [Fe] [Ca] Sample cium and magnesium. In addition, it can be seen that metal contam2800 197 1690 Turmeric Root ination from the packing material 18 12 Turmeric Extract 91 and metal fittings in an H P L C 0.5 0.12
