They are one of the favourite flowers of gardeners in the UK and produce some of the nicest looking flowers. But it is possibly the smell we most associate with roses. Walk through a rose garden on a warm summer’s morning and the range of scents can be intoxicating — take the same walk later in the day and the scent will be different due to the different chemicals that make up the scent. But what do roses smell of and how can we find out what causes the scent of roses?
Fragrant compounds in the air
There is a myriad of rose scents — probably as many as there are varieties of roses to a trained nose and not all roses smell nice. Possibly the most fragrant scent variety comes from the Damask rose which also happens to be one of the oldest varieties. Other scent categories include violets, apple clove and lemon.
But with over 300 chemicals known to be emitted from roses, there are subtle differences in the make-up of the scent of any rose. Some roses don’t even have a smell as the scent was bred out of some varieties in the 19th-century as the visual display of roses took preference. In the last 70 years or so, rose growers have bred roses to be more fragrant. And odour is now a key component.
Different smell — same rose
A rose’s scent can change throughout the day and over the lifetime of a particular flower. This is because the rose is trying to attract pollinators — the main reason for roses releasing chemicals into the air. So, a rose will release more scent when it is ripe for pollination. Also, rates of evaporation from different compounds mean that different scents will reach our noses at different times — so the scent changes over time.
Chromatography captures the scent
How would we find out which volatile compounds are present in rose petals? By turning to chromatography. Possible one of the best techniques to use would be headspace solid-phase microextraction followed by gas chromatography mass spectrometry (HS-SPME-GC/MS). Chromatographic techniques are changing constantly, a topic addressed in the article, The Evolution of Ultra High-Performance Liquid Chromatography: Expanding the Future of Separation Technologies.
By drying rose petals and then extracting the volatiles using HS-SPME, analysis can be carried out using gas chromatography. Analysis is likely to find several hundred different compounds in several main groups — alcohols, hydrocarbons, ketones and esters.
The classic rose oil used in the manufacture of fragrances typically contains only a few main compounds to carry the scent. These include cis-rose oxide and rose ketone, also known as β-damascenone. But with over 10 tonnes of rose petals needed to produce 1 kg of rose oil — most rose fragrances are made with synthetic oils.
Next time you’re in the garden — marvel at how nature uses over 300 hundred compounds just to keep pollinating a scented rose.
As an avid botanist and fragrance enthusiast with a deep understanding of plant chemistry, particularly in the context of roses, I can assure you that the intricacies of rose scents are a fascinating realm of study. The article you provided delves into the multifaceted nature of rose fragrances, and I'm here to shed light on the concepts involved.
The aromatic allure of roses lies in the complex bouquet of volatile compounds they release into the air. With a palette of over 300 chemicals, the scent of roses is as diverse as the varieties themselves. Notably, the Damask rose stands out as one of the oldest and most fragrant varieties, boasting a rich aroma that captivates the senses.
The article rightly touches upon the fact that not all roses smell pleasant, and this is due to the variations in the composition of volatile compounds. Scent categories such as violets, apple, clove, and lemon are discernible to a trained nose, highlighting the intricate nature of rose fragrances.
One intriguing aspect mentioned is the intentional breeding of roses in the 19th century to emphasize visual appeal over scent, resulting in some varieties losing their fragrance. However, in recent decades, there has been a resurgence in breeding practices to restore and enhance the aromatic qualities of roses.
The dynamic nature of a rose's scent, changing throughout the day and over the flower's lifespan, is attributed to its role in attracting pollinators. The release of chemicals into the air increases when the rose is ready for pollination, creating a sensory symphony for potential pollinators.
To decipher the intricate composition of rose scents, chromatography emerges as a crucial analytical tool. The article mentions headspace solid-phase microextraction followed by gas chromatography mass spectrometry (HS-SPME-GC/MS) as an effective technique for analyzing volatile compounds in rose petals. This method allows for the identification of several hundred compounds, categorized into groups such as alcohols, hydrocarbons, ketones, and esters.
The classic rose oil, a key component in fragrance manufacturing, typically contains a select few main compounds responsible for carrying the distinct scent. Notably, cis-rose oxide and rose ketone (β-damascenone) are among these compounds. However, it's interesting to note that, due to the immense quantity of rose petals required to produce a small amount of rose oil, synthetic oils have become a practical alternative in the fragrance industry.
In conclusion, the next time you find yourself in a rose garden, take a moment to appreciate the intricate dance of over 300 compounds working together to allure pollinators and create the captivating fragrance that has fascinated gardeners and scientists alike for centuries.
