I like to think that being a chemist makes me a good cook. Last time, I decided to try cooking a curry, and indeed, the recipe reminded me of the good old laboratory days; a list of ingredients, instructions about how to stir and how to add things sequentially. To top it up, the bright colours of the spices reminded me of the bright powders I used in my chemistry experiments. And indeed, I thought, knowing some chemistry does give insight into preparing a mouth-watering curry.
The first step is to fry the entire or the freshly ground spices in oil. Water does not do the trick since the molecules which give flavour are soluble in oil. Frying extracts the flavour from the dry spices and distributes it evenly in the sauce. The flavour in ginger is a result of a molecule called gingerol, which is converted to zingerone when heated. Chillies are an indispensable ingredient in every curry. The burning sensation is caused by a molecule called capsaicin, which in itself is flavourless. Capsaicin is also soluble in oil and, therefore, if you sink it in warm oil, it will give a much more intense flavour than if you use water.
The flavour in chillies, garlic and onion is due to sulfoxide molecules which are odourless. However, when the vegetables are chopped, enzymes change them to sulfenic acids. Further reactions result in numerous sulphur-containing organic molecules. Cooking changes the composition even further, producing a delicious aroma.
“Indian recipes, popularly known as curries, are a potpurri of flavours,” maintains Ganesh Bagler, a computational biologist from India. Indeed, Asian and Western cuisines follow different flavour rules. A study carried out in 2011 by researchers in Northeastern University, the US, shows that in Western cuisine, ingredients which share flavour molecules are assumed to taste better together (the food-pairing hypothesis). On the other hand, in Asian cuisine, ingredients which share the same flavour molecules are unlikely to be used together.
Preparing a good curry requires practice and I had to try a couple of times before I managed to get the taste I wanted. I must say, however, that buying a ready-made curry sauce does have its advantage; saving time. However, as Dan Toombs says in his book The Curry Guy: “Making delicious [curries] is all about building layer upon layer of mouthwatering flavour.”
Reference: Notman, N. Chemistry World, 2020, vol. 16, p. 22.
Maria Cardona is a chemist who loves reading, cooking and discussing aboute life. She read for her PhD in Padua as a Marie-Curie ITN Fellow Grant Agreement: 642793.
Did you know?
• When chopping onions, we cry because of syn-propanethial-S-oxide. This volatile molecule comes in contact with eyes and irritates them, resulting in tear production. Using a very sharp knife and cutting the onion very quickly might avoid this.
• Capsaicin binds to receptors in the tongue, sending messages to the brain indicating you are eating something hot. In order to cool the burn of a curry, wash the capsaicin from your tongue by drinking milk or a yoghurt-based drink, since capsaicin is soluble in the fat.
Reference: Notman, N. Chemistry World, 2020, vol. 16, p. 22.
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Sound bites
• Natural processes, such as muscle contraction, frequently require the self-organisation of small molecules into larger structures using energy from chemical fuels like ATP. When the energy is removed, the structure, e.g. a vesicle, is destroyed. Scientists found a way to imitate this. They designed nanocontainers which are only present during the lifetime of the chemical fuel. Watch here: https://www.youtube.com/watch?v=bePWMRMsPSU&t=1s Maiti, S. et al. Nature Chemistry, 2016, vol. 8, p. 725.
• A Maltese scientist produced similar transient vesicles. These form when ATP is added to a surfactant but are destroyed once an enzyme hydrolyses ATP. Two reactions were carried out. Reaction A occurs irrespective of the vesicles. Reaction B proceeds only when vesicles are present. Initially, before ATP is added to the surfactant, only reaction A proceeds. ATP is added and reaction B increases and becomes favoured, but only until the enzyme degrades the ATP. Eventually, reaction A becomes preferred again. This work proposes a novel way to control chemical reactivity in complex mixtures. Cardona, M.A. et al. Chemical Science, 2020, vol. 11, p. 1518.
https://pubs.rsc.org/en/content/articlelanding/2020/sc/c9sc05188k#!divAbstract
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