Mexican marigold (Tagetes erecta L.) is an herbaceous plant from the sunflower family, cultivated commercially for its yellow flowers, both as an ornamental plant and as a source of feed pigments and food colouring additives.
Mexican marigold is an erect annual herb that grows up to a height of 180 cm. The inflorescence is a solitary terminal head, up to 12 cm in diameter, bright yellow in wild types, lemon-yellow to deep brown-red in cultivated types. There are numerous (mostly ornamental) cultivars of Mexican marigold, differing in flower colour, flowerhead size and plant height (Setshogo, 2005).
Tagetes erecta flowers are rich in carotenoids and are used to make feed and food pigments. Lutein is the primary xanthophyll pigment that produces the orange colour in marigold flowers, comprising up to 90% of the petals’ identified pigments, with smaller amounts of antheraxanthin, zeaxanthin, cryptoxanthin, β-carotene and about 14 other carotenoids (Bosma et al., 2003; Setshogo, 2005). Tagetes erecta is a major source of lutein, since this pigment is not produced synthetically because the process is lengthy (Breithaupt, 2007). The marigold flowers are either dried and ground to create marigold meal or extracted with a solvent (see Processes below) to produce oleoresins, saponified oleoresins and purified lutein esters (Setshogo, 2005). The quality of these products for pigmentation depends on the level of trans isomers, on the level of saponification, stability against oxidation and the chemical isomerisation used to increase the concentration of some carotenoids such as zeaxanthin. The losses in pigmentation capability due to manufacturing or storage vary between 10 and 70% (Santos-Bocanegra et al., 2004). The nature of the other components of the premixture (minerals, etc.) also influences the stability of the extract (Magnin et al., 2009). Marigold pigments show good stability to heat, light, pH changes and sulphur dioxide. They are susceptible to oxidation, which can be minimized through encapsulation or the addition of antioxidants such as ethoxyquin, ascorbic acid, tocopherols or butylated hydroxyanisole and butylated hydroxytoluene. Marigold extracts are mixed with a carrier, such as edible vegetable oils, soybean flour, maize flour or distilled water (Setshogo, 2005; FDA, 2013).
Marigold meal and marigold extracts are used in poultry feed for colouring the skin, flesh (fat) and egg yolks (Martinez et al., 2004; Muñoz-Díaz et al., 2012), and more rarely in aquacultural feeds (fish and crustacean) (Setshogo, 2005). When authorized by local regulations, marigold extracts are used as a yellow to orange colorant in a wide variety of food products including baked goods and baking mixes, beverages and beverage bases, breakfast cereals, chewing gum, dairy product analogues, egg products, fats and oils, frozen dairy desserts and mixes, gravies and sauces, soft and hard candy, infant and toddler foods, milk products, processed fruits and fruit juices, soups and soup mixes (Cantrill, 2004). Fresh and dry flowers are also used to dye wool, silk and cellulose fibres (Setshogo, 2005).
In the European Union, naturally derived lutein is classified as E161b, but marigold extract has not been assigned an E number and is traded as vegetable extract. In the United States marigold meal and its extracts are approved only as colorants in poultry feed, but not in human foods (they have not been given FDA-GRAS status) (Setshogo, 2005).