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

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