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.

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’.

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 (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

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

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.

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!

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.

 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.

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!

 

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.

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?

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).

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’).

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 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

Can you smell that? Mmmmm, garlic.

A few nights back, I went to an Indian restaurant with my family. I do enjoy Indian food, but my favourite would have to be garlic naan! I also love garlic bread and garlic pizzas (are you sensing a theme here?).

Mmmmmm… But maybe not raw.

The garlic naan on this particular night, however, was a little bit tooooo garlicky. Some family members complained that it was spicy, as though pepper or chilli had accidentally been placed on top. However, this was just the effect of too much garlic! The chemical component of garlic which is responsible for this burning, spicy taste, is allicin.

Interestingly, allicin is not present naturally in garlic. When garlic is crushed or cut, enzymes then convert the compound alliin to allicin, which provides that well-known aroma. The use of heat with garlic will also cause this conversion, which explains why we smell that strong smell when cooking up garlic and onion for a Bolognese sauce, and not so much when the clove is sitting whole in our kitchen.

 

Allicin is only found once garlic is chopped or cut!

As for the other effect of garlic, bad breath, that is actually due mainly to four different chemical compounds, which are once again only observable in garlic once we cut, crush or chop it: diallyl disulfide, allyl methyl sulfide, allyl mercaptan and allyl methyl disulfide. You can find the structures on this great infographic from Compound Interest.

 

Of course, one of my favourite sites ever has an infographic on one of my favourite spices ever!

One thing you will notice in these structures is that they each contain an ‘S’. This ‘S’ stands for sulphur (or sulfur depending on where you come from!). Other things that you may think about when you hear are rotten eggs (the smell of which is made of hydrogen sulphide, H₂S) and fire/ volcanoes (‘brimstone’ is the ancient name for sulphur). Methanethiol, another sulphur compound, is believed to be one of those responsible for smelly urine after eating asparagus. But it’s not all bad news. Saccharin (an artificial sweetener), proteins, and penicillin all contain sulfur, and they’re not smelly… well at least not while they’re fresh.

It is thought that our dislike of sulfur-containing volatile compounds is due to our need to avoid unfresh foods. Some sulfur-containing compounds are produced when proteins in putrid food break down. Then the human body is able to detect these compounds, even at quite low concentrations, so that we know to avoid that particular food.

But (potentially) good news everyone. There are a couple of foods known to eliminate that lovely smell for when you want to kiss your loved ones or tone down the ‘spice’ of a meal. In cooking, you can use tricks such as roasting the garlic or leaving it to sit for ten minutes after crushing, or by adding potato or parsley to your meal. Parsley or milk, as well as as-much-gum-and-mouthwash-and-mints-as-you-can-handle are among your options for bad breath.

 

Chow down on a sprig of parsley, it’s supposed to help!

As a side note, some of the researched effects of garlic include antibiotic, anticancer, blood thinning, antiviral, and antifungal effects. So, to stink or not to stink?

Please see this website from the Linus Pauling Institute if you would like some more detailed information on Garlic and it’s health effects.

If you like drinking Coca-Cola, and getting caught in the rain…

Another requested post- this time on Coca-Cola! A warning first though: I do drink and like Coca-Cola, and what I write in this post is not meant to scare you or stop you from drinking it (especially with the chemical names), but to inform you. You are not a good or bad person for choosing what you eat or drink, BUT, please know that anything at all can be good or bad for you, depending on the concentration (even water!). Everything in moderation, brushing your teeth, and exercise to boot, is good!

I am guessing that many of you would have heard that Coca-Cola got it’s name because the original recipe included cocaine. But did you know why? The inventor, Colonel John Pemberton, became addicted to morphine after being wounded in the American Civil War. Even then, it was known that morphine was quite dangerous, and so in his quest to find a safer alternative, he happened across cocaine, and created ‘coca wine’ in 1886, formulated at his local pharmacy in Columbus, Geogia.

 

All hail John Pemberton, creator of Coca-Cola! 

Since then, the recipe has changed greatly, and while you won’t expect to get ‘high’ on Coca-Cola anymore, there is now the replacement ‘sugar high’. A quick look at the Australian Nutrition Information Panel shows us just that:

 

 The Nutrition Information Panels for Coke beverages are provided on their website.

Look at the second column (‘per serving’) on a can of Coke, and note that a serving size is 375 mL (the whole can of drink). For ‘sugars’, you will see 40 g. So, for every can of coca cola you drink, you are ingesting 40 grams  of sugar (or just over 2.5 tablespoons).

Of course, many of you are now saying ‘but I drink Diet Coke’, or ‘Coke Zero is much better for you, and that’s why I drink that instead’. It’s true, the Nutrition Information Panels for these ‘diet’ beverages show much less sugar; 0.4g in each (1/100^th of that in normal Coke). However, these drinks include other ingredients to keep the sweet taste. These ingredients are sweeteners 950 (acesulfame potassium) and 951 (aspartame), which give you the sweet taste without the calories (because we break them down in our body in a different way to sugars). Diet Coke and Coke Zero also include preservative 211 (sodium benzoate), which helps to prevent bacterial growth in acidic drinks, and food acid 331 or 330, which are different forms of citric acid.

      

Left to Right: See how different acesulfame potassium and aspartame are to table sugar (sucrose)? This is why they don’t provide calories: we break them down in a different way which doesn’t provide the body with energy.

One thing that is noticeable when comparing the three drinks is that the ‘diet’ beverages have higher levels of sodium; this is most likely because they contain preservative 211 (which contains sodium). Sodium is associated with some common health problems, including high blood pressure (hypertension). Sodium helps to regulate the volume and flow of blood in the human body. This is why we are told not to use too much salt (sodium chloride) in our meals, and to try to avoid processed foods (which are often high in sodium).

Coca Cola	Diet Coke	Coke Zero
Ingredients: Carbonated Purified Water, Cane Sugar, Colour (Caramel 150d), Food Acid (338), Flavour, Caffeine.	Ingredients: Carbonated Purified Water, Flavour, Colour (Caramel 150d), Food Acids (338, 330), Sweeteners (951, 950), Preservative (211), Caffeine.	Ingredients: Carbonated Purified water, Colour (Caramel 150d), Food Acid (338, 331), Flavour, Sweeteners (951, 950), Preservative (211), Caffeine.
Contains Caffeine. (approx.	Contains Caffeine. Contains Phenylalanine.	Contains Caffeine. Contains Phenylalanine.

 The ingredients and Nutrition Information Panels listed on cans.

Common to all three Coke beverages is food acid 338 (phosphoric acid), colour (caramel 150d; I think you can guess what that is for), flavour, and caffeine. You may have already seen my post on caffeine; if not: here it is! While the amount of caffeine is not stated on the label (and legally it doesn’t have to be), I have converted the values from this website to how many mg of caffeine we would see in one can of each drink, to find that Coca-Cola contains around 35.8 mg, Diet Coke 48.9 mg, and Coke Zero 37.8 mg. These values are less than half of what you would find in a cup of coffee (around 100 mg on average).

Another think that we can note with Coca-Cola is that it is quite acidic. This is due to the use of phosphoric acid and citric acid (the food acids shown on the label), as well as the use of carbonated water. In fact, the pH of Coca-Cola is measured as about pH 2.525. While my previous post on acidity assured you that drinking acidic drinks will not change the acidity of your blood, I did mention that “acidic drinks are associated with tooth decay, as they break down the enamel in our teeth”.

Enamel is on the outside, visible section of our teeth, and protects the vulnerable insides!

Enamel is the hardest tissue in the human body (due to its high mineral content), which is helpful considering that we use our teeth to chew and grind food down before swallowing! However, even the toughest human tissues can be broken: acids can eat away at tooth enamel and cause tooth cavities (ouchie!). Even worse is the fact that high-sugar foods and beverages (like cola) are consumed by natural bacteria in our mouths, producing lactic acid (which also increases the adicity of our mouths and affects our enamel). The problem with the loss of enamel is that our body can’t really replace it once it is lost, except partially by re-mineralisation (replacing minerals within your teeth). Yet another reason why Fluoride is not the enemy! Many dentists agree that fluoride within the water supply is very valuable in the remineralisation process.

So, I’m off to drink a can of Coke… and then brush my teeth!

Effect of drinking slightly acidic or basic water on the pH of the human body (Hint: It’s none)

A friend just asked me to de-bunk a post which has appeared on a particular facebook page for a water filter (*cough cough*).

No worries. This is dedicated to you, Linden!

The page states that they tested different water types for their acidity (with the kids, so you just know that they were following all of the correct laboratory safety protocols and statistical repeatability and reproducibility). They then stated that certain water brands were better for you, because they were less acidic. I especially loved the following: “With stress and foods causing acidity in our body, the only way to neutralise all of it is to drink alkaline water as we are made of 70% water.” (Sounds like a promotion to me!!)

Mmmm, I don’t know about that…

I’d love to do my own testing, and have a look at the pH of the different water types that they used, but I don’t have time at the moment, sorry! Anyway, what I would do is use a pH meter to check the approximate pH levels. Just to make sure that the claimee’s weren’t just using coloured dyes to make certain brands look good or bad, and because repeatability, reproducibility and more accurate equipment in analysis is always a good thing.

You stick the black probe in the water, press a button, and voila! A pH reading.

The regular pH of the human body is 7.4, just above the ‘neutral’ level 7.0. Lower than pH 7 is considered acidic (with more acidic solutions towards 1), and higher than pH 7 is considered basic/ alkaline (increasing in alkalinity up to pH 14).

pH values range from just under 1 to just over 14.

Different ions/ minerals may slightly change the pH of water. For example, ‘hard’ water (slightly basic) often contains calcium carbonate and magnesium (interestingly this means that when we use dishwashing detergent in hard water, it doesn’t lather as well). I should also note here that acidic drinks are associated with tooth decay, as they break down the enamel in our teeth- a post that I will be writing soon for another friend!

Also, one other side note, that I will address in another post: Fluoride is NOT the enemy. See this fantastic infographic about how fluoride has an undeserved reputation).

Fluoride is not going to kill us all. It’s actually there to help us pay lower dentist bills!

So, will stress, foods, or slightly acidic drinking water cause the pH level of our body to become acidic?

I would say a big fat NO.

Unless you are drinking sulphuric acid or concentrated sodium hydroxide, you are going to be fine (and I reckon that if you do ingest either of these, the burning down your throat would be the thing to worry you… DISCLAIMER: Do not drink either of these). 

If our body were to change in pH by only 0.05 either way, we would be in a bit of trouble. For a pH above 7.45, we would be undergoing alkalosis, and under 7.35 means that we’re experiencing acidosis. While these conditions are pretty serious stuff and include symptoms like headaches, confusion, muscle cramps and muscle pain, and potentially even coma, so are the causes. Acidosis occurs due to certain bodily organs being unable to carry out their normal job (e.g. the kidney in removing acids from our normal systems) or a build-up of carbon dioxide in the blood, due to hypoventilation (not breathing enough). Alkalosis, from repeated vomiting and severe hydration, or hyperventilation (breathing too much, meaning there is not enough carbon dioxide in our blood).

By now, you would have noticed that nowhere in those causes of acidosis or alkalosis were ‘drinking acidic or basic water’, ‘stress’, or ‘foods’.

The human body is an amazing thing, with so many different cells and systems and processes to keep us functioning each day. While the pH of our body should be around pH 7.4, the stomach is highly acidic at around pH 2.0, so that we can break down foods to access the nutrients we may need. Different parts of our body exist just fine at different pH. And we don’t need to drink certain types of water or eat certain types of food to restore our pH balance. Our body does that just fine on it’s own.

To decaf or not to decaf?

Many of you would have started today with a nice, big cup of coffee (or tea). I know I did. It always seems to help, especially on a Monday, to wake me up and get me going. But do you know anything about caffeine, the major cause of that ‘wake-up’? No doubt many of you would have heard of decaf coffee, but we’ll get to that later.

 

Ahhhh, the saviour of many a Monday morning.

Above is the culprit: caffeine. Caffeine is known to be the world’s most commonly used psychoactive drug (a scary-sounding definition which simply means that it works by stimulating the central nervous system of the human body). Like alcohol, it is a drug that is legal throughout most of the world, and caffeine is recognised as being safe for human consumption because the amount that we would need to consume to make it toxic is around 10 grams, which is far more than we get in coffee or tea (although excessive energy drinks are a little different).

Caffeine binds to adenosine receptors in the brain. 

Caffeine works by binding what are known as adenosine receptors, which are found in the brain. Above is a great picture which helps describe how it works when the caffeine structure binds the receptors. It causes you to feel more alert and awake, and also increases your heart rate. Because of this, caffeine has also been used to treat shortness of breath in newborn babies, and low blood pressure.

How much caffeine does the average coffee contain? The average cup of coffee is believed to contain approximately 100 milligrams of caffeine (about 1/50^th of a teaspoon), but it really depends on what your brand/ size/ bean/ strength is: it could be anywhere from 40-176 mg. Caffeine is not only found in coffee, but also in tea, and how much caffeine is in tea once again depends on what type of tea, and how the leaves have been treated before being made into a teabag for your cuppa. Interestingly, it was recently found that while tea leaves and cocoa beans both contain caffeine, they evolved in different ways to produce this much-desired stimulant (see Evolution of Caffeine for more information)

It’s ALWAYS coffee time! Get it? 😉 The lab technicians here have a good sense of humour.

Now on to decaf. Some of you may have ‘that’ friend who orders the venti soy decaf orange mocha frappucino (yes, I went there… Jitterbug). Personally, I like a weak latte, but to each their own. Anywho, from the word ‘decaffeinated’, you would probably guess that the coffee doesn’t contain any caffeine, and therefore does not give you that ‘buzz’ that coffee is known for. The fact of the matter is, however, that ‘decaffeinated’ does not necessarily mean ‘no caffeine’, but rather ‘much less caffeine’. In a 2006 study (outlined in this video by Mental Floss), it was found that from ten types of ‘decaf coffee’, nine of these contained 8.6-13.9 milligrams of caffeine (a freeze-dried coffee contained none at all). This is because caffeine is actually removed by dissolving the beans or grounds in water, which takes the caffeine out of the coffee and into the water (which is then discarded). This process works pretty well, but doesn’t remove all of the caffeine. So decaf coffees don’t remove all of the buzz, but do give you a much-reduced dose.

One coffee to rule them all…

So feel free to keep drinking your coffee or tea, it’s not going to kill you. Although drowning in that load of paperwork at your desk might.

GC-MS? What is that???

In a few of my previous posts, and a few yet to come, I mention Gas Chromatography- Mass Spectrometry (GC-MS). It is used when we want to be able to separate and identify the different chemicals which may make up a particular aroma, food, blood sample, soil, and the list goes on! This means that it can be used to identify many things, including drugs in urine samples, poisons in blood, explosive chemicals in soil, and as you would have picked up already in my blog (see Sniff Your Soy and Making wine smell like whiskey), the different chemical components which make up a particular smell. Now is as good a time as any to explain exactly what a GC-MS is, and how it works. It is quite a complex instrument, but I will try to explain it as simply as I can, so that you get the gist of why I will talk about it so much!

Here’s the picture of the GC-MS that I use!

The name Gas Chromatography- Mass Spectrometry gives you a hint that the instrument is made up of two separate parts. The GC part of GC-MS is used to separate different chemical compounds. A gas is set up to flow through a column, which is lined on the inside with particular chemical groups (for example, OH or NH or waxes). By injecting a chemical mixture (for example, the volatiles from soy sauce) down the column, the chemicals can be separated. They separate based on how big they are (larger chemicals may take longer to travel from one end of the column to the other), or how sticky they are to the groups lining the column (certain groups on the chemicals to be separated will try to hold on to the lining of the column, and take longer to travel through the column).

A schematic of a GC.

Once the chemical components are separated, they leave the column and are sent on to the detector.  The detector is the part of the instrument that helps us to work out what the compounds are, and even how much of each compound there is. There are many possible detectors, but in this case, we will just talk about a Mass Spectrometer (MS).

The word ‘mass’ gives you a hint that we are able to identify the different chemical components by looking at their mass. The MS is able to determine the identity of the compound coming off the column by looking at the mass of the compound, as well as the way that the structure can break apart. You see, we hit the chemicals with really strong, energetic hammers known as electrons. These electrons breaks the chemicals apart in very distinct ways, which give very distinct patterns depending on the chemical. So it is as though each chemical has it’s own ‘fingerprint’ map that we can identify it by (known as a mass spectrum).

The ‘fingerprint’ of dodecane, a chemical that is made up of 12 carbons bonded to hydrogens.

Using the MS, we can not only identify the chemical by its ‘fingerprint’, but we can also work out how much of each of these chemicals there are. This is because, on the readout produced by the GCMS (known as a gas chromatogram), it shows a series of peaks. Each peak is representative of one chemical that has been separated by the GC (if the separation is a good one), and therefore each peak would have its own mass spectrum. The area under these peaks tells us how much of the chemical there is, so the larger the peak, the more of the chemical.

A gas chromatogram: The larger the peak, the more there is of that particular chemical.

We can also use what we call ‘standards’. These standards are chemicals for which we know the chemical footprint, concentration, and how long it will take to travel through the column. So if we send the standard through the GCMS, we have an accurate description of not only how long it will take to appear in the MS detector, and how big the peak would be for a certain concentration.

Wow, that was a lot of information! If it helps, here is a five minute video which may explain GC-MS to you in a different way: http://www.youtube.com/watch?v=08YWhLTjlfo

Enjoy!

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).

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”).

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.

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…