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!


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.


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…