Spring 2002 Issue — Curcuma - Spice, Functional Food and Natural Remedy

K. W. Quirin

FLAVEX Naturextrakte GmbH

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Curcuma is a member of the Zingiberaceae/Ginger family. The pharmaceutically used varieties are C.longa/domestica, C.xanthorrhiza, C.aromatica and C.zedoaria. The first two are however the most important and C.longa is the commonly known spice turmeric which is an ingredient of curry powders and mustard and also applied as yellow colouring agent in food.

Meanwhile there is a huge number of articles available on curcuma research, phytochemistry as well as pharmacology which in this context cannot be considered and cited in detail.

Pharmacological efficacy

Numerous health benefits have been reported for different types of curcuma extracts produced with petrol ether, 50% ethanol and water. Most of the results are obtained by in vitro or in vivo animal studies but limited evidence is available to confirm the effects in humans. This situation is however improving today by new studies initiated by an increased interest in natural remedies without major side effects.

The positive effects are choleretic, antihepatotoxic, antihyperlipidemic, anti-inflammatory, antioxidative, anticarcinogenic, antimicrobial, antiviral and detoxifying.

For the group of curcuminoids the pharmacological studies reveal a reduced bioavailability/resorption if taken orally compared to a parenteral or peritoneal administration.

Curcuma extracts seem to be safe if applied in a pharmaceutical dose with respect to acute and chronic toxicity, mutagenity and teratogenity. For concentrated products however restricted dosage levels are recommended during pregnancy and for patients with gall-stones or with obstruction of the biliary tract. A highly dosed long term application may result in gastrointestinal disturbances/gastric ulcers.

Apart from this it is recommended to pay special attention on pesticide residues in turmeric preparations since these substances are sometimes enriched in curcuma rhizomes.

The petrol ether extract composed by mainly essential oil, the 50% hydro-alcoholic (HA) extract with a high curcumin content and the water extract of the rhizomes, which in this sequence mean an increase in polarity and a change in the extract composition show at least in some respects similar effects according to Table 1. Therefore it is a too simplified model to attribute the activity to the curcuminoids only.

It is well known for example that the components of the non polar essential oil are effective against chronic inflammation but the semi-polar phenolic curcuminoids and even some polar water soluble peptides, i.e. turmerin, are effective as well and contribute to the overall activity via different mechanisms.

Therefore turmeric might be a good example for a raw material where it makes sense to have both extract fractions, the lipophilic and the hydrophilic, the non polar and the polar one combined in a product for optimal benefits. This is especially important if the intention is to take advantage of all the positive effects of the material.

This consideration suggests a two step extraction strategy, i.e. first a lipophilic extraction preferably with supercritical carbon dioxide for the complete removal of the essential oil and other liposoluble ingredients followed by HA-extraction for the separation of more polar compounds. This sequence is reasonable since after the supercritical extraction the material is easier and more completely macerated or percolated by the polar HA-solvent due to the absence of oils. Since the HA-extract needs a more stressing work up for germ reduction and for solvent removal, i.e. distillation, followed by vacuum belt drying or spraying no loss or decomposition is anymore possible to the lipophilic, volatile fraction which has already been removed before by CO₂ - extraction and which can later on be recombined with the HA-extract.

Active constituents

The curcuma constituents can be roughly classified into polar/polymeric components, i.e. 30-40% starch, sugars and polysaccharides and some traces of interesting sulfur containing proteins, the semi-polar curcuminoids and the lipophilic volatile oil. Best investigated are the important curcuminoids and the essential oil fraction. Limited knowledge is available in the literature on other polar or lipophilic ingredients.

A comparison of the Curcuma longa and xanthorrhiza ingredients reveals according to Table 2 that the C.longa species has all three curcuminoids, curcumin as well as mono-and di-desmethoxy curcumin in a ratio of roughly 4:2:1 whereas the C.xanthorrhiza has no or only traces of the di-desmethoxy compound. The curcuminoid content is about three times higher for the C.longa compared to the C.xanthorrhiza rhizomes. In addition there are small amounts of other diarylheptanoids like cyclocurcumin and different hydrocurcumins.

Predominant compounds in the lipophilic essential oil fraction are monocyclic sesquiterpenes of the bisabolene type. The C.longa oil is characterized mainly by the sesquiterpene ketones of a-, b- and ar-(omatic) turmerone, which all make up more than 50% of the oil. In case of C.xanthorrhiza the sesquiterpene hydrocarbons of b- and ar-curcumene as well as the phenolic hydroxy-ar-curcumene (xanthorrhizol) are the predominant molecules with a concentration of more than 50% of the oil. The xanthorrhizol is specific for the C.xanthorrhiza species and cannot be found in other curcuma oils. C.longa contains typically 4% essential oil which is half the amount of C.xanthorrhiza with typically 8%. Besides these main compounds a huge variety of trace components has been identified in the lipophilic oil fraction. The chemical structure of the most important curcuma constituents is shown in Fig 1.

Fig.1

A screening has been done with dried curcuma fingers, representing material batches available in bulk on the European market with respect to the curcumin and essential oil contents and the essential oil composition (Table 3). Unfortunately the picture is not 100% complete concerning curcuminoids in case of C.xanthorrhiza since for CO₂ - extraction purposes the essential oil content is of major importance and the oil composition allows to verify the supplied variety. Nevertheless the figures might be interesting and they show that the Pharmacopoeia specifications for C.longa and C.xanthorrhiza which are given as headline are not easily met but mean a selected high grade quality.

Supercritical extraction

In case of curcuma supercritical extraction can favourably replace steam distillation as well as petrol ether extraction, i.e. produce a high grade lipophilic extract under well standardized conditions containing all essential oil components and other lipophilic ingredients. CO₂-extraction can however not replace hydroalcoholic or water extraction.

Standard conditions for curcuma extraction are a pressure of 25 MPa and a temperature of 50°C and a high relative solvent ratio kg CO₂/kg curcuma in order to extract the lipophilic components completely. Nevertheless such a total extract is composed by more than 80% of volatile essential oil components besides other non volatile substances. If a selective extract, i.e. the pure essential oil should be separated the pressure can be reduced to 12 MPa. The concentration of the semi-polar curcuminoids even in the total CO₂ -extract is only 0,15%, in comparison to HA-extracts with roughly 10-20% curcuminoids from the C.longa and 5-10% from the C.xanthorrhizamaterial.

Supercritical CO₂ -extraction with ethanol as entrainer increases the curcuminoids in the extract. It complicates however the procedure and is less effective than the hydroalcoholic extraction. Therefore a two step extraction strategy should be preferred.

Table 4 shows the composition of the CO₂ -extracted essential oils of C.longa and C.xanthorrhiza, both of Indonesian origin. The analysis was done by GC according to the 100% method and trace components of less than 0,2% have not been considered. Thus substances like curcumol, curcumenone, curdione and others are not indicated in the table. The oils were extracted with CO₂ at 12 MPa and 50°C, conditions which allow the complete removal of the essential oil but leave back most of the non volatile lipophilic components in case of curcuma anyway a small proportion. It is obvious that the turmerone related compounds make up 50% of the C. longa oil and the curcumene related substances including hydroxycurcumene (xanthorrhizol) make up 50% of the C.xanthorrhiza oil which is typical for both species. As expected substances like cycloisoprene-myrcene and b-tolylmethylcarbinol which have been reported for curcuma oils in the past but are identified as distillation artifacts today could not be detected in the CO₂ -oils.

The figures in Table 4 are only examples. The composition differs depending on origin, climate, variety etc. of the botanical material. A better valuation of the curcuma oils is possible, when the oil components are classified into monoterpene (C10) hydrocarbons, sesquiterpene (C15) hydrocarbons and into oxygenated mono- and sesquiterpenes as demonstrated in Table 5.

Table 5

If these groups are considered it is obvious that the monoterpene hydrocarbons, about 10% in both oils are not the valuable and specific ingredients. They are common substances in many other essential oils. The oxygenated monoterpenes certainly have some activity but the most important and specific components are made up by the low volatile proportion of the sesquiterpene hydrocarbons (25%) and the oxygenated sesquiterpenes (40-50%). The last group requests long distillation times, especially since these low volatile substances are the major oil components and since the total oil content of the material is high, i.e. typically 4% for the C. longa and 8% for the C. xanthorrhiza species. Unfortunately at the same time the oxygenated sesquiterpenes are sensitive molecules forming artifacts under long lasting thermal stress.

Therefore steam distillation is not the best procedure in order to separate the poorly volatile curcuma oil. Remains extraction with low boiling organic solvents like petrol ether which is also not well accepted because of the high temperature needed for solvent removal and because of the solvent residue problem in the extract.

It thus can be concluded that supercritical CO₂ -extraction is the state of the art technology in order to obtain the essential oil (selective extract) or all lipophilic components (total extract) of curcuma quantitatively and without decomposition. Supercritical CO₂ is an excellent solvent for the lipophilic curcuma components without leaving any solvent residues and the CO₂ - extraction parameters can be well standardized and reproduced.

Conclusion

Supercritical and hydroalcoholic extracts of C.longa and C.xanthorrhiza or preferably a combination of both extract types are safe and promising candidates for the formulation of nutraceuticals and natural remedies with protective, detoxifying and cancer preventing properties fighting against oxidative stress and inflammation and thus against wide spread deceases found in civilized countries.

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