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Valentine’s Day! Time to Smell the Roses!

There is a lot of interesting chemistry in that classic fragrance.

There are more red roses sold on Valentine’s Day than on any other day of the year. They hold a special place among flowers, particularly because of their associations with romance. In Greek mythology, Aphrodite, The Goddess of Love, fell in love with the mortal shepherd Adonis. When he was gored by a wild boar, she rushed to his aid but as she brushed by a wild rose bush her skin was pierced by its thorns. Aphrodite’s tears mixed with her blood and dripped on the rose bush which thenceforth produced the red roses that came to symbolize love and passion. Cleopatra is said to have covered her boudoir with rose petals when she welcomed Mark Antony, and guests at Roman orgies supposedly had their passions flamed by the scent of rosewater in the air.

The simplest form of rosewater was produced by steeping rose petals in water. This certainly smelled like roses but did not have exactly the same bouquet as a freshly picked flower. Rose fragrance is a complex mixture of dozens of compounds, some of which are water soluble, other not. For example, geraniol, a major component of rose aroma is water soluble, but beta-damascenone, another important contributor, is not. A much more fragrant rosewater became available with the introduction of the alembic, a basic distillation apparatus, generally attributed to the Islamic alchemist Jabir ibn Hayyan in the ninth century.

The alembic was a rounded flask with a long neck that to this day is identified with the practice of alchemy. A substance placed in the flask is heated from below and the vapours formed then travel through the long neck where upon cooling they condense to a liquid that can be collected as it drips out from the end. When rose petals were placed in the alembic along with water, the steam that formed helped to vapourize the volatile components. The product of such “steam distillation” is the “essential oil” of the rose and floats on top of an aqueous layer, the “hydrosol,” that contains the water-soluble components. It is this hydrosol that is generally referred to as “rosewater.”

The essential oil, also known as “attar of roses” is used in perfumery, while rosewater can be used to flavour beverages or sweets such as marzipan and Turkish delight. Rose attar can also be produced by agitating the petals in a vat with a solvent such as hexane. Such “solvent extraction” draws out the fragrant compounds along with waxes and pigments. Subjecting the extract to vacuum removes the solvent that can then be recycled leaving behind a waxy mass that is then treated with alcohol. The alcohol dissolves the fragrant components and when it is evaporated under low pressure, the essential oil or “absolute” is left behind. It can take more than two thousand flowers to produce a gram of oil which means that rose attar is very expensive. This invites adulteration generally by dilution with oil of geranium which is rich in geraniol but is much cheaper. There is no health issue, but such “extended” oils should not be referred to as pure attar of roses.

It isn’t surprising that a popular flower like the rose should have invited investigation for possible medicinal properties over the ages. The ancient Greek physician Dioscorides recommended an elixir of roses cooked in wine for headaches, while Native Americans treated colds, coughs and fevers with various concoctions derived from the flowers, leaves or roots of the plant. Rosewater has also been used cosmetically, incorporated into creams for its supposed anti-inflammatory properties.

Such traditional uses, while mostly anecdotal, have stimulated some serious research into potential medicinal properties, especially since roses do contain numerous terpenes, glycosides, flavonoids and anthocyanins with potential pharmacological effects. Unfortunately, virtually all the studies have been carried out in animals or in cell culture with a paucity of human data. For example, aromatherapists have claimed that rose essential oil can have a soothing, sleep-inducing effect. However, the citations provided deal with mice. When mice are put to sleep with a barbiturate, their sleeping time increases if their food is supplemented with some specific rose extracts. Only specific extracts work and only at doses far greater than any to which humans would be exposed. Furthermore, the extracts were ingested, not inhaled.

Rose extracts have also been claimed to have a pain-killing effect. What is the evidence? When mice are treated with an ethanolic extract of roses and then are placed on a hotplate, they flick their tails less frequently than in the absence of the extract. Hardly enough to warrant a prescription for humans. As far as purported antimicrobial effects go, rose essential oil has been shown to be effective against a variety of microorganisms in a petri dish. There is nothing surprising here, numerous plant extracts show such effects but that is a long way from showing an effect in human infections.

While roses may have no practical medicinal effects, their visual splendor and striking fragrance have come to be associated with affection and an appreciation of the beauty of life. A great gift on Valentine’s Day!


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