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!
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…