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Turmeric (Curcuma longa) is an important spice and colouring agent and has been used for more than 2000 years. Turmeric is native to South and South-East Asia and is used in many dishes, especially in curries. The yellow colour of most curries is derived from turmeric. The colour is obtained from the roots of the plant, which are ground to a crude powder.
Fig. 1 :Turmeric root and powder (Source)
The main compounds in turmeric are curcumin (fig 2) and its derivatives demethoxycurcumin and bis-demethoxycurcumin. The latter differ from curcumin in that the CH3-groups are removed. The ratio between the three pigments differs between preparations, but curcumin is present in the highest concentration and bis-demethoxycurcumin in the lowest concentratin.
Fig. 2 : Structure of curcumin
Curcumin is not soluble in water, but dissolves in oils and alcohol. It is quite stable and gives a bright orange-yellow colour to products. In Asian cuisine turmeric is mainly used as a spice, whereas in Western countries the main use is as a colouring agent.
Curcumin is not stable under alkaline conditions above 7.5, which do not occur in many foods. Curcumin is light sensitive but stable at temperatures used in food processing. Light sensitivity is decreased by the addition of aluminium ions, which form a complex with curcumin and thus protect degradation by light.
Nowadays curcumin salts are also available, which are water soluble and thus increase the range of products in which curcumin can be used.
Turmeric and curcumin are widely used in foods and cosmetics. Applications include canned beverages, baked products, dairy products, ice cream, yoghurts, yellow cakes, biscuits, popcorn-colour, sweets, cake icings, cereals, sauces etc.
Curcumin also acts as an antioxidant and has been added for this purpose to oils and fats. It also protects against rancidity in bakery products, such as cakes.
Turmeric has also been used as a traditional medicine in India and other Asian countries, but it is not used for these purposes in foods or food supplements.
Delgado-Vargas, F. and Paredes-López, O. (Eds): Natural colorants for food and nutraceutical uses. CRC Press, 2003.
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