Bergamotene

Aroma and sensory profile

Bergamotene is a quiet sesquiterpene with a good name. Fragrance references describe (E)-alpha-bergamotene, the main natural isomer, in three words, woody, warm, and tea [2], and the alpha-bergamotene entry itself carries no organoleptic description at all [1]. It does not smell of bergamot; it is named for bergamot oil, where it is a trace constituent [2], and the citrus character of that oil comes from limonene, linalyl acetate, and linalool. What bergamotene contributes, in basil and bergamot and carrot seed alike, is a soft, dry, tea-like woodiness underneath the brighter monoterpenes.

The molecule is a bicyclic sesquiterpene on a pinane-type skeleton, 2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1.1]hept-2-ene [3], with two stereocenters and one exocyclic double bond, so it exists as cis and trans (Z and E) geometric isomers, each a pair of enantiomers, alongside the beta-bergamotenes with the ring double bond moved. Fragrance databases list the (E)-alpha form and a cis-alpha form separately. No panel description of the individual enantiomers was found, so no claim about how they differ in odor is made here.

Effects and research

No animal or human study of bergamotene was found. Its research is chemical ecology, and it is one of the better-studied cases of a single volatile doing two jobs.

In the wild tobacco Nicotiana attenuata, (E)-alpha-bergamotene is emitted from flowers, where it enhances pollination by adult hawkmoths, and from leaves after herbivore damage, where it mediates defense against those same moths' larvae by attracting their predators; a single terpene synthase gene, expressed differently in the two tissues, controls both emissions, which resolves the dilemma of a plant whose pollinator is also its herbivore [5]. Transgenic tobacco engineered to over-produce (E)-alpha-bergamotene and (E)-beta-farnesene showed that these sesquiterpenes quench ozone locally and transiently but do not protect the plant from ozone, ultraviolet, or drought stress, pointing to a biotic rather than abiotic role [6]. Tobacco engineered to make bergamotene became attractive to green peach aphids, which the authors proposed as the basis of a trap crop [7]. These are results about insects and plants, not about people, and nothing in them implies an effect of inhaling or ingesting the compound.

Natural sources

Bergamotene is a minor constituent almost everywhere and a major one in a few unlikely places. Fragrance databases record (E)-alpha-bergamotene at 6.8 to 9.6 percent in sweet basil oils and extracts, 3 percent in Turkish basil, 0.16 to 0.44 percent in bergamot oil, 0.73 percent in carrot seed oil, and traces in anise, celery seed, cumin, and cinnamon leaf [2], and the alpha-bergamotene entry adds 10.7 percent in Alpinia galanga oil, 1 percent in calamus root oil, and traces in grapefruit, guaiacwood, and lemon oils [1]. Its richest known source is the Iranian mint-family herb Teucrium hircanicum, whose oil carried (E)-alpha-bergamotene at 17.5 to 86.9 percent across ten wild populations [4]. Wild tobacco emits it from flowers and damaged leaves [5]. In cannabis bergamotene is a minor sesquiterpene, reported in a few chemotypes alongside caryophyllene.

Boiling point and vaporization

No measured boiling point for bergamotene appears in PubChem or in a primary paper found for this profile, so none is listed. PubChem carries no experimental boiling point for alpha-bergamotene [3]; fragrance references quote 259 to 260 °C at 760 mmHg for both the alpha and (E)-alpha entries [1][2], an industry value not adopted here, and the 213 °C the site previously listed had no traceable source. What can be said is that bergamotene is a fifteen-carbon hydrocarbon sesquiterpene like caryophyllene and humulene, so it belongs in the base-note band and persists in dried basil and stored oils. Its ecological role as an airborne signal shows it is volatile enough to travel between plants and insects at ambient temperature [5]. No thermal degradation study of bergamotene was found.

Industries and uses

Fragrance: bergamotene contributes a warm, woody, tea-like depth in basil, bergamot, and herbal accords and is used as a natural constituent of those oils rather than as an isolated material [1][2]. It arrives in a composition through sweet basil oil, where it reaches nearly 10 percent, through bergamot and carrot seed oils at well under 1 percent, and through galangal and calamus root oils [1][2]. No flavor, aromatherapy, or cosmetic use specific to bergamotene was found in the sources reviewed, so it carries no other industry tag here.