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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Olive Oil- Can you tell the difference between extra virgin and ordinary? Maths can!

Time for this week’s QJART!

Linking Chemical Parameters to Sensory Panel Results through Neural Networks to Distinguish Olive Oil Quality

Cancilla JC, Wang SC, Diaz-Rodriguez P, Matute G, Cancilla JD, Flynn D, & Torrecilla JS

Journal of Agricultural and Food Chemistry 62 (2014) 10661-10665

oliveoil2

Yum. And that’s all I have to say about that.

I don’t know many people who don’t love to dip a piece of fresh bread into some extra virgin olive oil. But would you be able to taste the difference between extra virgin and ordinary virgin olive oil? It’s okay, you don’t have to: Mathematics will do it for you!

In order to combat the growing trend of adulterated or falsely-labelled olive oils, researchers in Madrid, Spain have developed a method through which differences between extra virgin olive oil (EVOO), virgin olive oil (VOO), ordinary virgin olive oil (OVOO), and “lampante” olive oil (LOO, natural olive oil not fit for consumption). To do so, they used the combination of a sensory panel and the measurement of six chemical parameters of 220 olive oil samples, and then applied nonlinear mathematical modelling known as artificial neural networks (ANNs), which allow for the discovery of “nonlinear trends that exist between variables”.

First, the sensory panel were asked to evaluate the olive oils based on attributes considered desirable (green, ripe, and bitter) and related to defects (earthy, vinegar-like and muddy). They were also asked to grade the oils as EVOO or other.

Six chemical parameters were also measured in each oil; free fatty acid content (FFA, related to the acidity of the oils), peroxide value (PV, a measure of oxidation), two UV absorption parameters (K232 and K268), 1,2-diacylglycerol (DAG) content (a component found in a range of 1-3% in virgin olive oils), and pyropheophytin content (PPP, a degradation product of chlorophyll which is found in olive oils that have degraded through age or heat). The different graded olive oils provided different values for each of these tests.

oliveoil3

Hmmm, they all look the same… but taste different and contain many of the same chemical components, but it different quantities!

ANNs were then used to link the results from both the chemical analyses and sensory evaluation, and through the identification of various relationships, were able to correctly classify (on average) 96% of olive oils. The researchers did note that while the ANNs used are have been successful in other food and chemistry-related scenarios, that the particular modelling used may not be as successful when looking at samples different to those used in this study.

Think about that the next time someone tells you that maths is useless after high school: it’s helping save you money at the supermarket every time you buy olive oil!

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

Sniff Your Soy?

When was the last time you had a sniff of soy sauce? Personally, I don’t think I ever have. Sure, I love pouring soy sauce all over my dumplings when I visit my favourite Dumpling restaurant in Richmond, but I don’t hold the bottle up to my nose and take a whiff. Although the next time I visit XiaoTing Box, I may do just that.

Here is this week’s QJART!

Characterisation of aroma profiles of commercial soy sauce by odour activity value and omission test

Yunzi Feng, Guowan Su, Haifeng Zhao, Yu Cai, Chun Cui, Dongxiao Sun-Waterhouse, Mouming Zhao

Food Chemistry 167 (2015) 220–228

These researchers, from China and New Zealand, looked at the different aroma compounds which make up the smell of soy sauce. They investigated twenty-seven commercial soy sauces, produced through three different fermentation processes; high salt liquid state(HLFSS), low salt solid state (LSFSS) and Koikuchi (KSS).

Soy sauce manufacture

The three fermentation processes use different soybean:flour ratios, salt concentrations, microorganisms, and bacterial fermentation times.

When you are next at your local chinese restaurant, and smell the soy sauce at the table, I’d like you to guess how many different compounds make up that smell. One? No. Ten? No, higher. A billion? Okay, maybe not that many. But this research identified 129 compounds that were volatile (able to enter your nose because they are in their gas form), and of these, more than 41 compounds which produce a smell (“aroma active components”).

dumpling soy sauce

Mmmm, dumplings and soy sauce…

The aim of this research was to identify what impact, if any, the different fermentation processes have on the smell and flavour of soy sauce. The researchers were able to do this by sensory evaluation (where a panel of ten trained judges smell and describe the soy sauce), as well as by analysing the volatile components by Gas-Chromatography-Mass Spectrometry (GC-MS). A GC-MS deserves its own blog post, so while I have not yet described how a GCMS works, I will tell you now that it enables us to separate, identify and quantify these different volatile compounds.

PIC_0059

A photo of a GC-MS that I currently work with.

An interesting point that you will come across in many of my future blog posts is that once we separate out the different chemicals which contribute to the smell of something, we find that they each smell like something that in no way represents the smell of the food as a whole. For example, just a few of the chemical compounds in soy sauce include 3-(methylthio)propanal, guaiacol, benzeneacetaldehyde, and 3-methylbutanal, which on their own would smell like cooked potato, smoke, honey and malt. Another interesting point is that we may not be able to smell some of these volatiles until they are at a certain concentration (known as an odour threshold).

The panel of ten judges for sensory evaluation underwent ‘omission experiments’, where the panel were provided with an aroma ‘model’ (made up of most, but not all, of the aroma compounds of soy sauce) to compare against the complete aroma of soy sauce. In all cases, the panel were able to tell which sample was the complete aroma. This is helpful as it allows the researchers to see which particular aroma compounds (omitted from the aroma model’ make the most impact in the smell of soy sauce.

There were many differences in both the GC results and the sensory evaluation across the different soy sauces and fermentation processes, and the authors noted that the differences in the overall aroma of the soy  sauce was due more to the concentrations of the individual aroma compounds, than the variety of compounds.

I think I know what I want for dinner tonight…

More Retronasal Bonito, Monsieur?

Generally, if people decide that a food is too bland at the dinner table, they add salt. However, more and more people are being made aware of the problems that salt (in particular, sodium) can cause to the body: high blood pressure, kidney problems, and even stroke. So what do we do?

Add dried bonito stock, according to Japanese researchers.

Bonito is a type of fish, and dried bonito stock and flakes are commonly used in Japanese cooking, especially soups. They are associated with umami flavour.

Bonito Stock

Bonitooooooooooo.. Used in miso soup!

The interesting part here is how we as humans are able to perceive the smell of bonito. It doesn’t come through sniffing food through our nose (known as the orthonasal pathway). Instead, we perceive the aroma of bonito through the retronasal pathway- that is, after we chew (and even swallow) our food, the aroma is released and travels from our mouth into our nasal cavity.    

Retronasal Bonito

A photo of the setup used to provide retronasal bonito aroma (taken from the article).

Using two forms of bonito stock (arabushi and karebushi), the researchers tested if retronasal bonito enhanced the saltiness of foods (which it didn’t) and also if it increased the palatability of food (which it did).

While this is all well and good, one thing that the researchers note is that bonito, while delicious and flavoursome and enjoyed by many Japanese, is not as appreciated in other cultures. Therefore, bonito may not be the answer to everyone’s low-salt-tasteless-diet woes.  

The Article: Retronasal Odor of Dried Bonito Stock Induces Umami Taste and Improves the Palatability of Saltiness

The Authors: Mariko Manabe, Sanae Ishizaki, Umi Yamagishi, Tatsuhito Yoshioka and Nozomu Oginome

The Journal: Journal of Food Chemistry, 2014

Time to start posting!

So, after a very lengthy break, I’M BACK! I wanted to start off with something that will hopefully become a common theme on my blog, and that is reviews of articles related to food science, food analysis and sensory evaluation of food… So here you go!

It’s Quick-Journal-Article-Review-Time! Or QJART as it shall now be known. This QJART is based on the following article:

     Effect of vine foliar treatments on the varietal aroma of Monastrell wines

     A.I. Pardo-García, K. Serrano de la Hoz, A. Zalacain, G.L. Alonso & M.R. Salinas.

     Food Chemistry 163 (2014) 258-266

It turns out winemakers can induce grapes to smell like smoke/ clove or whisky.

This area of research began after it was noted that grapes from areas which had experienced forest fire activity were producing wines with a smokey flavour. It was realised that the foliar treatment of certain volatile/ aroma compounds (such as those present in smoke) to grape vines was allowing the storage of these compounds as non-volatile glycosides (basically, by joining the volatile to a sugar molecule). Then, during the wine-making process, the volatiles could be released to provide their associated smell.

The analysis involved the use of Gas Chromatography- Mass Spectrometry (GC-MS) to identify the aroma/ volatile compounds in the grapes/ wine, as well as analysis of the amount of glycosidic compounds by High Performance Liquid Chromatography (HPLC), and sensory analysis by a team of eight expert judges. These analyses were completed at three stages of the winemaking process: at the end of the alcoholic fermentation, and malolactic fermentation (the addition of bacteria), as well as six months later.

Using eugenol and guaiacol (smoke aroma compounds), and whiskey lactones (you guessed it, they make up the aroma of whiskey) in Monastrell red grapes, researchers in Spain identified an increase in glycoside content in grapes, but noted that there was little transferrance to wines, suggesting that these glycosides are stored in the grape’s skins. Also, the storage of guiaiacol in grapes was associated with lower sugar content (leading to lower alcohol levels in wine).

Even though the transferrance of aroma compounds to wines was quite small (an increase of 8-12% at most), tasters were still able to identify clove (eugenol and guaiacol) and woody/oak (whiskey lactone) flavours.

No word on when we will be receiving the first batch of ‘bacon’ wine.