Nootkatone

Nootkatone is an important constituent of grapefruit flavor. The title material has an extremely powerful fruity, sweet, and citrusy odor of good tenacity.
Almost colorless, or pale yellowish oily liquid when pure. Some commercial grades are orange-colored, slightly viscous.
Practically insoluble in water, soluble in alcohol and oils.

Discovery:

This bicyclic, conjugated sesquiterpene ketone is relatively new even in the research laboratory. It was identified in Grapefruit peel oil and juice in the early 1960s and shortly after this discovery, a method of synthesis was developed, based upon a component of sweet Orange juice oil, Valencene.

Natural Occurrence:

Nootkatone occurs naturally in Grapefruit peel oil in which the material may be present at a rate of about 0.3%.

Other Uses:

[5] –– Nootkatone in spray form has been shown as an effective repellent/insecticide against deer ticks and lone star ticks. It is also an effective repellent/insecticide against mosquitos and may repel bed bugs, head lice, and other insects. It is an environmentally friendly insecticide because it is a volatile essential oil that does not persist in the environment. It is non-toxic to humans, is an approved food additive, and is commonly used in foods, cosmetics, and pharmaceuticals.

[5] –– The CDC has licensed patents to two companies to produce an insecticide and an insect repellant. Allylix, of San Diego, CA (Now Evolva), is one of these licensees and has developed an enzyme fermentation process that will produce nootkatone more cost-effectively.

Profile:

• 📂 CAS N° 4674-50-4

• ⚖️ MW — 218.33 g/mol

• 📝 Odor Type — zesty - citrus

• 📈 Odor Strength — Very high. Threshold 800 ppb.

• 👃🏼 Odor Profile — Woody, vetiver, fruity citrus, tobacco, grapefruit, zesty powerful grapefruit, peel note, earthy.

• Strongly fresh, green, sour; dusty-woody; animal-erogenic, slightly herbal, fruity (John C. Leffingwell, Ph.D.)

• 👅 Flavor Profile — was perceptible at a concentration of approximately 0.3 ppm and still had the flavor character of grapefruit. — [6]

• Nootkatone has a pleasant taste in concentrations lower than 50 ppm, and although preliminary reports indicate that the material has a perceptible flavor down to 1 ppm, the author is inclined to claim that the minimum perceptible for Nootkatone is between 0.1 and 0.2 ppm.
  The interesting fact is that the material has a typical Grapefruit peel taste at levels higher than 3 ppm and lower than 50 ppm. — [1]

• ⚗️ Uses — Citrus compositions, grapefruit boost, woody vetiver notes. can be helpful in the gunpowder note.

The title ketone could undoubtedly find use in perfume compositions for novel effects in top note compositions, etc., particularly in combination with Bergamot oil, Bitter Orange oil, Hexenyl esters, Aldehydes, etc. — [1]

Production:

The sesquiterpene Valencene is isolated from Orange juice oil (a plentiful by-product) and oxidized with tertiary-Butyl chromate to yield the title ketone. — [1]

It is synthesized by oxidation of valencene, which is obtained and isolated from orange peel oil where it occurs at a maximum level of 0.4%.
For the oxidation of valencene to nootkatone, strong oxidation agents like oxygen in the presence of metal salts, peroxides, or chromate compounds are required. There are also several patents on the bioconversion of valencene to nootkatone which results in natural nootkatone. — [2]

Notes:

Nootkatone has been approved as G. R.A.S. by the American Food and Drug Administration, and it has been used very successfully in new carbonated beverages, etc. A highly purified synthetic product is now generally used. — [1]

Fruit maturity has a major impact on peel oil composition. Terpenes are almost exclusively present in the oil from an unripe fruit. As fruit mature, concentrations of aliphatic aldehydes and oxygen-containing terpenes, and sesquiterpenes increase. For example, nootkatone and α-selinenone were not detected in the peel oils from fully developed immature fruit, but the oil from ripe fruits contained up to 0.15% of these oxygenated sesquiterpenes. — [2]

Two character impact compounds have been proposed for grapefruit flavor, the first being nootkatone, a sesquiterpene. The fresh juicy note of grapefruit juice is attributable to 1-p-menthene-8-thiol. This compound has a detection threshold of 10􏰢1 ppt, among the lowest values reported for aroma chemicals. The (􏰧)-R-isomer was found to have a lower aroma threshold in water than the racemic mixture, and it imparts a pleasant, fresh grapefruit juice character, as opposed to the extremely obnoxious sulfur note contributed by the (􏰢)-S-epimer. — [3]

Sources and information:

1. Perfume and flavor chemicals 1

2. Flavors and Fragrance Chemistry Bioprocessing and Sustainability

3. Flavor, fragrance, and odor analysis

4. A fragrant introduction to terpenoid chemistry

5. Wikipedia

6. The Nootkatones, John C. Leffingwell, Ph.D.

7. National Center for Biotechnology Information (2020). PubChem Compound Summary for CID 1268142, Nootkatone. Retrieved November 24, 2020 from https://pubchem.ncbi.nlm.nih.gov/compound/Nootkatone.