QJART: 2015 is Year of the Goat! Have you ever drank goat’s milk?

Milk is milk, right? Actually, different seasons, farming and heat treatment play an important role in the chemical makeup (and therefore taste and aroma) of many of the foods and beverages we consume, including milk. If you have ever tried goat’s milk, you might remember it being “more robust, waxy, and animal-like” compared to cow milk.

Here's looking at you, kid...

Did you know goats produce around 2% of the world’s milk? I didn’t!

Researchers in Germany have recently looked at goat’s milk in more detail, by analysing the aroma compounds and sensory differences between goat’s milk from two different farms and seasons (Winter and Summer), as well as the changes produced through different heat treatments (pasteurised, UHT-treated and sterilized).

Aroma profile analysis (APA) consisted of a trained sensory team analysing the raw milk samples, of different farms and seasons, through orthonasal (sniffing) and retronasal (where you swallow a sample with your nose pinched, and then release your nose to find you can still smell the sample) olfaction. Eight attributes were measured, including milk-like, fatty, goat-like, stable-like, and hay-like. Not only were differences found between orthonasal (where milk-like and fatty dominated the aroma) and retronasal (goat-like and fatty), but also between milks of different farms. The panel also identified summer-produced milk as smelling more ‘milk-like’, while winter milk was rated more ‘goat-like’. Meanwhile, the highest ratings for the pasteurised and UHT-treated milks were goat-like, and sterilised milk noted as ‘caramel-like’.

Milky milky goodness.

No point crying over it… Fact of the matter is that raw goat milk has a good chance of smelling like goat! 

The odour-producing chemical compounds were identified by Aroma Extract Dilution Analysis (AEDA) using Gas Chromatography-Olfactory (GC-O), to determine the instensity of the individual components contributing to the overall aroma. AEDA involves diluting the original milk samples to various levels, running each dilution through GC to separate the individual chemical components, and then sniffing the components through a nose port. In the winter and summer milks of both farms, 54 odour-active volatile compounds were detected, with 4-ethyloctanoic acid (4-etC8 which smells goaty or stable-like), 3-methylindole (or ‘skatole’ which smells fecal or stable-like) and an unknown (canola-like, metallic, green) identified in the most dilute samples, yet at different dilution levels for each season and farm.

For the heat treatment milks (pasteurised, UHT-treated and sterilized), 66 odor-active compounds were identified: 4-etC8 and skatole were once again present in the most dilute samples, along with phenylacetic acid (honey-like) and in the sterilised milk, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (or furaneol, which is caramel-like in odour and explains the APA description). From this, we can assume (and chemistry does support) that it is the heat treatment process that produces the sweeter taste!

Furaneol produces a caramel or cotton candy/ fairy floss smell.

Furaneol (above) smells like caramel or cotton candy/ fairy floss. Yum!

Side note: I also found this great infographic comparing goat and cow milk, made using information from the US Department of Agriculture. Each has it’s benefits and disadvantages, but if you enjoy your sense of taste and smell, you might want to steer clear of goat milk.

Siefarth C & Buettner A (2015).

The Aroma of Goat Milk: Seasonal Effects and Changes through Heat Treatment.

Journal of Agricultural and Food Chemistry 62: 11805-11817

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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.