Coriander

The plant and the material

Coriander seed oil is the oil from the seeds of coriander. The dry fruits are coriander seeds. In food preparation the word coriander may refer solely to the seeds, as a spice, rather than to the plant. Cilantro is the Spanish word for coriander. Cilantro is the common term in US English for coriander leaves, but the seeds are referred to as coriander in American English.

The species is native to the Mediterranean Basin. It grows wild over a wide area of West Asia and Southern Europe, which makes it difficult to define where the plant is native and where it was only recently established. It is a soft plant growing to 50 cm (20 in) tall. The flowers are borne in small umbels, white or very pale pink. The fruit is a globular, dry schizocarp. The variety sativum has a fruit diameter of 3-5 mm, the variety microcarpum 1.5-3 mm, and the variety indicum has elongated fruits.

Chemistry

Linalool, a terpenoid, is a major contributor to the fragrance of coriander. Coriander leaf and seed oils contain mixed polyphenols and terpenes, and linalool is the major constituent accounting for the aroma and flavour. The main flavorant in the seeds is (+)-linalool. Linalool comprises about two thirds of the volatile components of the seeds. (S)-Linalool, also called dextro-linalool, is a major constituent of the essential oil of coriander. In food manufacturing, linalool may be called coriandrol.

Linalool makes up 60-80% of the essential oil, with geraniol at 1.2-4.6% and terpinen-4-ol at 3%. Camphor is present at 0.9-4.9%, geranyl acetate at 0.1-4.7% and linalyl acetate at 0-2.7%. In seed oils from nine Iranian and Iraqi populations, oxygenated monoterpenes made up a great proportion of the oils, with linalool as the major compound. Linalool was the most abundant compound in these oils, from 63.77% in the Urmia population to 74.15% in the Baghdad and Dezful populations.

Seed and leaf

The taste of the leaves differs from that of the seeds. The seeds exhibit citrus overtones. The dominant flavorants in the leaves are the aldehydes 2-decenal and 2-dodecenal. The leaf oil has an unpleasant odor due to the presence of aliphatic aldehydes. Because of variations in the gene OR6A2, some people perceive the flavor of coriander as more soaplike or rotten. That gene encodes a receptor that is highly sensitive to aldehyde chemicals.

Variation in the oil

Soil and climatic conditions, altitude, irrigation and other biotic and abiotic factors affect the composition of the essential oil. Among 19 accessions analyzed in Iran, oil yield ranged from 0.1% to 0.36% and linalool content was 60-70%. Coriander seeds grown in the cool, wet conditions of Atlantic Canada yielded a higher oil content. Seed storage temperature strongly affects the percentages of monoterpenes and sesquiterpenes in coriander seed essential oil. Sesquiterpene compounds were found in the oil of immature seeds, but they disappeared in ripe seeds. Large-fruited types are grown mainly by tropical and subtropical countries, such as Morocco, India and Australia, and contain a low volatile oil content of 0.1-0.4%.

Safety

Some people are allergic to coriander leaves or seeds, with symptoms similar to those of other food allergies. Some 7% of people undergoing patch testing in Europe were found to be allergic to the oxidized form of linalool.

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