Chemistry: Bulgarian Journal of Science Education, Volume 21, Number 6, 2012 Природните науки в образованиетоAdvanced Science Наука за напреднали и самообразование PHYTOCHEMISTRY OF TURMERIC: AN OVERVIEW Bizuneh Adinew Mizan-Tepi University, ETHIOPIA Abstract. The review intended to describe the phytochemistry of turmeric (curcumin longa). Turmeric contains a wide variety of phytochemicals, including curcumin demethoxycurcumin, bisdemethoxycurcumin, zingiberene, curcumenol, curcumol, eugenol, tetrahydrocurcumin, triethylcurcumin, turmerin, turmerones, and turmeronols. Among these, the most active component of turmeric is curcumin which gives a yellow color to turmeric and responsible for most of the therapeutic effects. The physico-chemical properties of curcumin are dependent on the pH of the medium. This review helps of chemists to understand the phytochemistry of curcumin and its medicinal values in a better way. Keywords: curcumin, phytochemistry, turmeric, curcuminoids Turmeric Turmeric (Fig. 1) is valued mainly for its principal coloring pigment, curcumin, which imparts the yellow color to turmeric, besides other nutritive constituents like potassium (Peter, 1999). The main coloring constituent of turmeric and other yellow Curcuma species is curcumin. Curcumin is the product obtained by solvent extraction of turmeric, i.e. the ground rhizomes of Curcuma longa L. (Curcuma domestica Valeton) and purification of the extract by crystallization. Coloring principles are present to the extent of 3-5 % in turmeric. In fact, besides curcumin there are a few other related pigments which impart the yellow color, all together called 888 Fig.1. Indian turmeric (from Wikipedia) 7-bis (4-hydroxy-3-methoxy-phenyl)-1.Phytochemistry of Turmeric: An Overview OH 8 9 10 3 5 6 4 O H O 2 1 2` 4` 3` 5` 10` 9` 8` OH 7 OMe 7` 6` MeO Curcumin ([1. 2. Structure of curcumiminoids from C. longa 889 .6-heptadiene-3. 5-dione] OH OH H O H O O Me Demethoxycurcmin [4-hydroxy-cinnamoyl (4-hydroxy-3-methoxycinnamoyl) methane HO OH H O H O H bis-demethoxycurcmin [bis-(4-hydroxy cinnamoylmethane] Fig. 2001) Curcumin Hypocholestremic (Blasiak et al.7-bis (4-hydroxy-3-methoxy-phenyl)-1. eugenol. Curcumin is hydrophobic in nature and freely soluble in dimethylsulfoxide. triethylcurcumin. 2003) Anti-bacterial (Katsuyam et al. Phytochemistry of turmeric Turmeric contains a wide variety of phytochemicals. 3).heptadiene-3.inflammatory (Aggarwal & Harikumar. 2).. This process after distillation of the solvent yields an oleoresin with coloring matter content in the region of 25-35 % along with volatile oils and other resinous extractives. 2001) Wound healing (Biswas & Mukherje.. 1999) Anti-carcinogenic effect (Mosly et al. Curcumin oxidation yields vanillin. The oleoresin so obtained is subjected 890 . acetone. curcumenol. 6.. demethoxycurcumin [4-hydroxy-cinnamoyl (4-hydroxy-3methoxycinnamoyl) methane and bis-demethoxy curcumin [bis-(4-hydroxy cinnamoylmethane] together make the coloring pigment in the turmeric rhizomes (Fig. It has an absorption maximum around 420 nm (Abas et al. The most active component of turmeric is curcumin which makes up 2 to 5% of the spice. 2008) Antioxidant (Ruby et al. Medicinal properties of curcumin Extraction of curcumin Curcumin is extracted from the dried root of the rhizome Curcuma longa. and washed with a suitable solvent that selectively extracts coloring matter. including curcumin demethoxycurcumin. bisdemethoxycurcumin.. 1999). and turmeronols (Chattopadhyay. oils and insoluble in water.. 3. turmerones. insect repellant (Tawatsin et al. et al. zingiberene. 2007) Diabete (Pari & Murugan. 2004). 1995) Fig.. chloroform. Curcumin [1. tetrahydrocurcumin. curcumol. 2007) Anti. Curcumin is the phytochemical that gives a yellow color to turmeric and is now recognized as being responsible for most of the therapeutic effects (Fig. ethanol. turmerin.. 5-dione]. 2009) Hepatoprotective effect (Song. 2005).Bizuneh Adinew curcuminoids (Verghese. The process of extraction requires the raw material to be ground into powder. 1985). but they rapidly decompose at pH above neutral. Preparations of water-soluble curcumin by incorporation into various surfactant micellar systems (e.11 was studied using HPLC technique (Tonnesen & Karlsen. purified food color.and A3) have been determined to be 7. In the pH range 1-7.5. 8. In solutions the principal coloring components of curcumin exhibit keto-enol tautomerism and. it is found that ethyl acetate. At pH <1. The kinetics of hydrolytic degradative reactions of curcumin over the pH range 1. The selection of solvents is done with care to meet extractability and regulatory criteria. Table 1.0. the color changes to red and the pKa values for the dissociation of the three acidic protons in curcumin (forms H2A-. gelatine. polysaccharides. At pH>7.g. Solvents used for extraction of curcumin from turmeric Solvent Isopropanol Ethyl acetate Description In the curcumin manufacturing process isopropyl alcohol is used as a processing aid for purifying curcumin With a restriction placed on the use of chlorinated solvents. known as curcumin powder. with over 90 % coloring matter content and very little volatile oil and other dry matter of natural origin. Physico-chemical properties Curcumin is an oil-soluble pigment. The following solvents are considered suitable (Table 1). is a reasonable replacement providing acceptable quality of product and commercially viable yields This is used as a solvent in the curcumin manufacturing process This solvent is used sparingly because curcumin is completely soluble in ethanol Acetone Ethanol The principal coloring components of curcumin are relatively stable at acidic pH. up to 95 % are in the enol form. aqueous solutions of curcumin have a red color which indicates the protonated form (H4A+). owing to its polarity. polyethylenglycol. sodium dodecyl sulfate. respectively (Fig. cetylpyridinium bromide.Phytochemistry of Turmeric: An Overview to further washes using selective solvents that can extract the curcumin pigment from the oleoresin.4). This process yields a powdered. and soluble in alkali. the majority of curcumin species are in the neutral form (H3A).5 and 9. Water solubility is very low in this pH range and solutions are yellow. practically insoluble in water at acidic and neutral pH.8. cyclodextrins) have been reported (Tonnesen. depending on the solvent.. 2002). In a study of alkaline degradation of 891 . HA2. such as dichloroethane. 1973). The evaluation of the total amount of curcuminoids in a sample by use of direct absorption measurements is only valid if the calculations are based on reference values obtained from pure standards. be noted that the presence of other compounds absorbing in the region of 420-430 nm influence the results strongly. For an exact determination of the curcumin content a pre. The curcuminoids isolated from C. curcumin. which are chemically related to its principal ingredient curcumin. 2). All three impart the hallmark yellow pigmentation to the Curcuma longa plant and particularly to its rhizomes. It should however. Most of these are spectrophotometric methods. Based on these the structure of curcumin was established as diferuloylmethane..430 nm in organic solvents.. 1986).5 is representative.. 1985). Commercially obtained Curcuma products contain mixtures of curcumin. 1995). 1998). demethoxycurcumin and bisdemethoxycurcumin. longa exhibit strong absorption between 420 . curcumin are not particularly stable to light. On boiling with alkali. expressing the total color content of the sample. vanillin. demethoxycurcumin and bis-demethoxycurcumin (Fig. Chemistry of curcuminoids The coloring principle of turmeric was isolated in the 19th century and was named curcumin. The initial degradation products are formed after 5 minutes and the chromatographic pattern obtained after 28 h at pH 8. Although the chemical structure of curcumin was determined in the 1970’s and 1980’s. recently the potential uses of curcuminoids in medicine have been studied extensively. The difficulties in obtaining reproducible results could be ascribed to the difference in fluorescence intensity of curcumin and the two demethoxy compounds 892 . a cyclisation product was detected. Analysis of curcuminoids A variety of methods for quantification of the curcuminoids were reported (Tonnesen & Karlsen. products of decomposition at pH 7-10 were determined by HPLC. such as vanillic acid.Bizuneh Adinew curcumin (Tonnesen & Karlsen. and ferulic acid (Sasaki et al. The structure of curcumin as diferuloylmethane was confirmed by the degradative work (Majeed et al.separation of the three curcuminoids is essential. curcumin gave vanillic acid and ferulic acids whose structures were established. Three curcuminoids were isolated from turmeric viz. In addition to this. The official methods for assaying curcumin or curcuma products as food color additives are based upon direct spectrophotometric absorption measurements. A direct fluorimetric method for the assay of curcumin in food products was reported (Karasz et al. On hydrogenation a mixture of hexahydro and tetrahydro derivative were obtained. as well as decomposition products. especially in solutions. Curcuminoids refers to a group of phenolic compounds present in turmeric. Fusion with alkali yielded protocatechuic acid and oxidation with potassium permanganate yielded vanillin. After the photo-irradiation of curcumin. 4. Structure of curcumin at different pH values 893 .Phytochemistry of Turmeric: An Overview HO ОН+ H 4A + OMe OH HO OH ОН OMe H3A MeO O HO OH ОН OMe H 2A MeO OMe O HO O- О- HA2MeO O OMeО Fig. Unterhalt. 1981. the number of free silanol groups is kept at a minimum. Quantitative analysis of curcumin and related compounds by TLC or HPLC is difficult to carry out unless the chromatographic support is properly deactivated. the detection limit lying in the picogram range (Tonnesen & Karlsen. Krishnamurthy et al. The adsorption is therefore ascribed to intermolecular hydrogen bonding between the keto-enol unit of the 1. 1984). Spectroscopic methods (IR. 1973. GC methods provide no alternative to HPLC due to the low volatility and thermally labile nature of the curcuminoids. strong mineral acids or boric acid (Karasz et al. and then the possibility of using quantitative MS in curcumin analysis could be evaluated. Smith & Witowska. Janssen & Gole. Separation of the curcuminoids is strongly dependant on the chromatographic conditions. Curcumin and the related 1. HPLC systems based on C18 stationary phases did not completely resolve the three curcuminoids (Asakawa et al. 1976. At fixed excitation and emission wavelengths (420 .. The detection limit for curcumin in biological samples by MS needs to be determined. To increase the molar absorptivity of curcumin. seems to have a catalytic effect upon curcumin degradation. 1972. 1984). Janssen & Gole. It was reported that the strong interactions observed between curcumin and silanol groups 894 . 3-diketones are shown to adsorb strongly onto the silicic acid used as the solid support in TLC and HPLC. Roughley & Whiting. 1980). A pre-separation of the curcuminoids can be accomplished by thin-layer chromatography (TLC) or high-pressure liquid chromatography (HPLC) (Tonnesen & Karlsen. and MS) are widely used for identification and characterization of the curcuminoids (Tonnesen & Karlsen. 1983). NMR. e. A reproducible separation of the colored compounds was achieved by the use of an amino bonded stationary phase. By removing one of the keto groups from a diketone the adsorption to silica gel can be prevented (Tonnesen & Karlsen. However. 1980.g.470 nm)..Bizuneh Adinew in organic solvents. intensely colored complexes were developed by reaction with alkalis. 3-diketones and the silicic acid.. however. Govindarajan. Mass spectrometry (MS) is often the method of choice when trace amounts of organic compounds are to be detected. 1983). 2:10. provided that the water content of the system is kept below 10%. HPLC system based on an amino-bonded stationary phase. Unless these differences are taken into account small changes in sample composition may lead to large variations in the curcumin content calculated. the colors formed were found to be very unstable and severe fading was reported after 5-10 minutes with the exception of the boric acid complexes (Dyrssen et al. NMR has also been tried for quantitative determinations (Unterhalt. To obtain reproducible results the experimental conditions must be carefully controlled. 1973. 1986). 1984). 1980). 1983)..4 at equimolar concentrations (Tonnessen & Karlsen. 1986. the relative fluorescence intensities of curcumin. 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