I do love pancakes and maple syrup…

In a few of my posts, I have alluded to the fact that the different odours that we perceive are actually made up of a number of volatile (gas) chemical compounds. These mixtures can be of anywhere from three to a billion (okay, maybe over exaggerating) chemical components to give a certain smell, like that of soy sauce or maple syrup or wine.

800px-Sotolon_chemical_structure

 Sotolone is the theme for today’s post!

In this post, I want to talk about an individual aroma compound that is really interesting to me- sotolone (or sotolon). It is a type of lactone, and it’s full chemical name is 3-Hydroxy-4,5-dimethylfuran-2(5H)-one. The interesting part about this molecule is that it smells different at different concentrations! For example, if you were to smell a really strong solution of sotolon, it would smell like curry, or the herb fenugreek.

fenugreek

This is fenugreek: it goes by quite a few other names!

However, if you were to smell more dilute (weaker) solutions of sotolone, it would smell like maple syrup, or caramel, or burnt sugar. How very different- going from something spicy in nature to something quite sweet smelling!

 maple syrup

I think I am starting to write my posts based on what I want to eat…

Sotolone can be found in soy sauce, beer, wine, ‘candy cap’ mushrooms, raw cane sugar, and many other foods and beverages, and is the source of the smell of artificial maple syrup. It is also found in the urine of people who suffer from something called ‘maple syrup urine disease’! The disease is “a recessive inherited disorder of branched-chain amino acid metabolism due to deficiency of the branched-chain alpha-keto acid dehydrogenase complex”- which in basic terms means that the sufferer does not have the correct enzyme to break down amino acids (from proteins) correctly in their body, and so produce sotolone which is excreted from the body in urine.

While I can’t find any information as to how we perceive something to smell different due to its concentration, I will leave you with this video: ‘How Do We Smell?’ by Rose Eveleth, on how we take chemicals from the air and turn them into something we can smell.

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Breathe deep, tea drinkers.

Sorry for my lack of posting over the last few weeks, but I have had the amazing opportunity to go to the UK for 10 weeks for research, and spent last week recovering from jet lag, learning English slang (like ‘having a nosey’) and setting myself up! Anywho, it’s QJART time!

Anyone who is a lover of tea, or has visited the tea shop T2, would recognise that different teas have different characteristic aromas, which depend on the leaf type and manufacturing process. But what makes up the smell of green tea?

green tea

A nice green tea in a green cup with a green teapot… So green, must be environmentally friendly! 😉

Three cultivars of Chinese green tea (Longjing, Maofeng, and Biluochun) were analysed by researchers in Japan to identify which volatile compounds make up the characteristic aroma of green teas. They began by first extracting the volatiles from the tea infusions, using a method called ‘SAFE’ (Solvent Assisted Flavour Evaporation).

SAFE unit

The distillation unit used in SAFE is quite complex!

This method involves first the solvent extraction of the volatiles from the teas, followed by the use of a specialised glassware and high vacuum pump system to extract the tea volatiles from the solvent. The volatiles are then concentrated to give the SAFE extract, which can be used in gas chromatography-olfactory (GC-O) (an instrument which first separates the volatile components and then allows you to sniff these volatiles through an attached ‘nose’).

GCO

See that in front of her nose? That’s the ‘nose’ where you smell the separated volatiles!

To identify which volatiles contributed the most to the green tea aroma, the authors used Aroma Extract Dilution Analysis (AEDA). In AEDA, the SAFE extract is diluted a number of times, to give different Flavour Dilution (FD) factors. For example, diluting the original sample by four in solvent will give an FD of 4. Diluting again will give an FD of 16, and continuing on will give 64, 256, 1024, and so on, multiplying by four each time. The whole idea behind these dilutions is that the concentration of the individual components should become weaker and weaker with each dilution. Therefore, if we can still smell a particular volatile at the highest FD factors using GC-O, then it is associated with being a major component of the aroma.

Fifty eight odour-active peaks (separated volatile components which had a smell) were identified in the teas, at different concentrations in the different cultivars. Of these, seven had the highest FD factors in all tea cultivars, and are therefore believed essential for the aroma of Chinese green tea, including vanillin (smells like vanilla), geraniol (smells ‘green’), and (E)-isoeugenol (smells floral or spicy). The authors further suggested that (E)-isoeugenol, which was newly identified in Chinese green tea, was a product of the manufacturing process rather than the leaves themselves.

E-isoeugenol

(E)-Isoeugenol smells floral or spicy, and is a volatile found in the aroma of green tea.

Next time you sit down with your cuppa, take in a deep breath through the nose, and admire those volatiles.

Baba R, Kumazawa K (2014) Characterization of the Potent Odorants Contributing to the Characteristic Aroma of Chinese Green Tea Infusions by Aromatic Extract Dilution Analysis. Journal of Agricultural and Food Chemistry 62: 8308-8313