Extraction and Characterization of Essential Oils from Basil Varieties

Introduction

According to Vina and Murillo (and references within), the essential oils from the basil plant (Ocimum spp) can be grouped in three chemical families: phenylpropanoids, monoterpenes, and sesquiterpenes. Phenylpropanoids are plant compounds that are derived from the non-oxidative deamination (loss of ammonia) of the amino acids phenylalanine and tyrosine by the enzyme PAL. Monoterpenes and sesquiterpenes are composed of 2 and 3 isoprene subunits, respectively, and believed to be synthesized through the mevalonate pathway.

Based on these three chemical families, Vina and Murillo defined "3 profiles:"

phenylpropanoid-rich, phenylpropanoids > monoterpenes > sesquiterpenes (profile 1)

monoterpene-rich, monoterpenes > phenylpropanoids > sesquiterpenes (profile 2)

sesquiterpene-rich, sesquiterpenes > phenylpropanoids > monoterpenes (profile 3)

Of the 12 varieties of basil investigated by Vina and Murillo, 7 varieties are labeled profile 1, 4 varieties are labeled profile 2, and only 1 variety is labeled profile 3. The chemical compounds that occur most frequently in basil include, methyl cinnamate (a phenylpropanoid), linalool (a monoterpene), and 1,8-cineole (also a monoterpene).

Other chemical compounds that appear to be common amoung these 12 varieties include methyl chavicol (a phenylpropanoid also known as estragole and p-allylanisole), caryophyllene (a sesquiterpene), pinene (a monoterpene), myrcene, limonene (a monoterpene), ocimene (a monoterpene), terpineol (a monoterpene), methyl eugenol (a phenylpropanoid), bergamotene (???), guaiene (a sesquiterpene),farnesene (a sesquiterpene), selinene (a sesquiterpene), germacrene (a sesquiterpene), cadinene, spatulenol, epicubenol, and cadinol (a sesquiterpene).

Although the monoterpene and sesquiterpenes represent a diverse and important group of chemical compounds, they are of less interest to us since these compounds are relatively stable in a biological environment and do not undergo chemical reactions involving oxidative chemistry, our primary interest.

The essential oil composition from "basil" is significantly different depending on the specific variety and other factors including growing conditions. For culinary purposes, these details are less important since the character of the basil can be evaluated by tasting the leaf prior to food preparation. When essential oils are used for medicinal purposes, the chemical composition of the oil needs to be characterized using the technique of gas chromatography-mass spectrometry (GC-MS).

References

Essential oil composition from twelve varieties of basil (Ocimum spp) grown in Colombia

Amparo Viña; Elizabeth Murillo* Departamento de Química, Facultad de Ciencias, Universidad del Tolima, Ibagué, Tolima, Colombia

Infraspecific Taxonomy and Essential Oil Chemotypes in Sweet Basil, Ocimum basilicum.