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Identity and properties

Raspberry ketone, 4-(4-hydroxyphenyl)butan-2-one, is a ketone in which the phenyl ring of 4-phenylbutan-2-one carries a hydroxy group at position 4. Its CAS number is 5471-51-2, its molecular formula is C₁₀H₁₂O₂ and its molecular weight is 164.20. It forms white needles that melt at 82 to 84 °C. It boils at 140 to 146 °C at 0.5 mmHg. It is insoluble in water and in oil, and soluble in alcohol, ether and volatile oil. Its predicted pKa is 9.99. The name Frambinone is evidently derived from framboise, the French word for raspberry.

Occurrence

The smell of raspberries is due to lots of molecules, but raspberry ketone is the impact molecule associated with their particular smell. Over 200 molecules have been identified in raspberry flavour. Terpenoids, ketones and aldehydes make up the majority of the emissions from raspberries, with variation between cultivars, whereas strawberry emissions are dominated by esters, up to 90% in some cultivars. Among the important compounds with smells characteristic of ripe fruit are α- and β-ionone, β-damascenone, linalool and geraniol. Raspberry ketone is also found in other fruits, including cranberries and blackberries. It has also been reported in loganberry and sea buckthorn. It is biosynthesized from coumaroyl-CoA. In plants the pathway starts with a condensation of p-coumaroyl-CoA with malonyl-CoA. The flower of the orchid Bulbophyllum apertum has raspberry ketone in its nectar and attracts males of several fruit fly species of the genus Bactrocera.

Authenticity of natural material

Natural raspberry ketone commands a premium in the flavour industry, so methods have been devised to check the biosynthetic origin of the molecule. These include 12C:13C isotope ratios, which depend on the biosynthetic pathway, and site-specific natural abundance 2H NMR. Other molecules present, such as the ionones, can also be monitored by gas chromatography-isotope ratio mass spectrometry.

Cost and marketing

Raspberry ketone is one of the most expensive natural flavor components used in the food industry. The natural compound can cost as much as $20,000 per kg. Products containing this compound are marketed for weight loss, but there is no clinical evidence for this effect in humans. Tests on mice indicate an antiobese effect, believed to be due to increased lipolysis and fatty acid oxidation, but as far as is known no tests on humans have been reported. Little is known about the long-term safety of raspberry ketone supplements in humans. Toxicological models indicate potential for cardiotoxicity and effects on reproduction and fetal development. No international regulatory authority has approved raspberry ketone as a weight loss supplement or established whether it is safe to use.

Other uses

Raspberry ketone is used as an intermediate for liquid crystals. It also occurs as an impurity in the synthesis of dobutamine.

The fruit

Raspberries are the edible fruits of several species of the genus Rubus, in the rose family, most of them in the subgenus Idaeobatus. The red raspberry, Rubus idaeus, is native to Europe and northern Asia and commonly cultivated in other temperate regions. A raspberry is an aggregate fruit of numerous drupelets, and when it is picked the receptacle stays on the plant and leaves the fruit hollow. An individual raspberry weighs 3 to 5 g and is made up of around 100 drupelets. World production in 2023 was 940,979 tonnes, led by Russia with 23% of the total. Other major producers were Mexico, Serbia and Poland.

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