Ljiljana Fruk: exciting enzymes

How does a chemist become a chocolate designer?
31 March 2020

Interview with 

Ljiljana Fruk, Cambridge University


Close-up of a dark chocolate bar.


Chemist, advisor to the chefs, chocolate designer and expert on things at very small scales, Ljiljana Fruk told Chris Smith what she gets up to in her research...

Ljiljana - Yeah. So I work... in my research we explore two things: we work on extreme small scales, so we use nanotechnology, very small dimensions; and we work with materials which we can pack in such a way that they resemble the sizes of our biomolecules in our organism. And enzymes are really extremely good chemists. So they're responsible for speeding up reactions in nature. And they are also very specific. That means that they can choose one reaction, sometimes out of many reactions, and just specialise on this one. But then they specialise perfectly. And you can imagine that these enzymes are then particularly useful for chemical industry. If we could design enzymes that could help us to do these reactions that we need, to produce clothing or produce some food, we would be really happy because we will reduce the waste, they are usually biodegradable. So we try to take the inspiration from natural enzymes, those which are present in our organism or in some plants and animals, and we try to simplify them so that we can design materials which are relatively cheap, but they can still do the reactions that we would need. So for example, we designed the simplified enzyme that can make indigo dye. And indigo dye is, for example, a blue dye that you use in your clothing. So everybody who has a little bit of jeans today definitely has the indigo dye. And this is produced in chemical industry with numerous processes that produce lots of waste. If you use enzymes, you simplify these reactions. So you know, instead of having 20 reaction sequences to get this indigo, you now have three. And you work with reagents which are really sustainable. So this is what we do. And our materials look like this.

Chris - You've got a demo to show us enzymes in action.

Ljiljana - I have a demo, exactly. And you know, before, we were using oxygen to burn things; now I am going to use the enzyme to produce the oxygen. And this will do hopefully, it will do well. I have my lovely assistant here. I'll take the glasses - safety first. I have also a lab coat, which all chemists should have. And I have gloves. And what I have here, and you see - a little bit of special treatment, I have a very big flask and there are some small flasks here - I have hydrogen peroxide in this flask. And hydrogen peroxide is similar to water; so water has one oxygen and two hydrogens; hydrogen peroxide has one additional oxygen, which makes it a little bit more reactive, but it makes it also very good for different household activities. So you probably, if you look in your kitchen or in your bathroom, you might find some products, cleaning products, that have hydrogen peroxide. So what I have then here, it's a mix of yeast, normal baking yeast that you can buy in the shop, which has an enzyme called catalase. It's a very powerful enzyme, it works really within the second, and it can degrade this hydrogen peroxide into water and oxygen. So let's see if we can make this reaction go.

Adam - So we're going to pour the yeast into this philosophy of peroxide.

Ljiljana - Yes. Wooo! So what we actually get here... and if you would touch this flask now, you would realise that it's really hot and you can see it foaming.

Adam - So foam just shot out of the top. Yes.

Ljiljana - So we put a little bit of detergent in it, a little bit of soap, so that we created the foam.

Chris - Ljiljana, is that science-speak for 'we cheated'?

Ljiljana - Yes, because I wanted to make it visualised! How else would you see the oxygen? Oxygen you can't see. So we made oxygen visible. So you have lots of oxygen produced, and this reaction also releases lots of energy, so basically everything heats up.

Adam - I notice there are four more flasks.

Ljiljana - I know, yes! I need four volunteers from the audience. Yes! Oh my God, who's going to be faster? How are we going to choose? Yeah, you have to put some glasses on...

Adam - Safety first, we need lab equipment...

Ljiljana - Lab coats on!

Adam - Science is the most glamorous activity in the world. Purple gloves, matching white coats. This year from Ralph Lauren.

Ljiljana - Yes. And then you have your purple gloves. Okay, take the position. Choose your flask.

Adam - Choose wisely.

Ljiljana - And choose wisely. So you do have your flasks, which we prepared already because we put a little bit of hydrogen peroxide in the flask and we put a little bit of soap. I will move out of the way. Here you have your mix of the enzyme, yeast; you need to start your reaction and do your reaction, and you need to do it by pouring the enzyme into your mix. Are we ready?

Adam - Go, go!

Ljiljana - Go, go, go, go, go! Yay! Oh wow. That's much better than I have done. Wow, look at that foam.

Chris - What did you think of that, David Rothery? I mean, I've asked you about your favourite planet; have you got a favourite experiment?

David - Well that was fun. I mean, watching that liquid turn to foam, which expanded its volume and caused it to shoot up through the long necks of those flasks, was a very good physical analogue of what happens inside volcanoes. The chemistry is different, but when you have a liquid... when a sudden amount of gas gets formed, and it forms bubbles and it changes the volume, it can drive stuff upwards. That's why volcanoes erupt. Because the gases dissolved in the magma come out of solution, turn into foam, and push it up the conduit of the volcano. If it's more explosive than what we saw here, it can break that foam into fragments, and that's what volcanic ash would be. But you very sensibly controlled it here so it didn't break into fragments, and was just a foam and spilled out like bubbly lava. But the physics behind what you showed there is the same as happens in volcanoes. It's just gas expanding the volume and driving the molten stuff up the pipe to the surface.

Chris - Quick question for Ljiljana -  now where's Joe? Joe says he's 10, and wants to ask about famous chocolate bars. Where are you Joe?

Joe - What's the most famous chocolate bar you've worked on?

Ljiljana - Ah, that's a trick question. So I didn't work on any of the brands you will know. But I have here one chocolate, which I think is going to be very famous soon. And this is a chocolate which we developed to celebrate a birthday of Nikola Tesla, who's a famous physicist. And he has done lots of experiments with electricity. And he comes from a region in Europe which is famous for plums and berries, so we designed the chocolate - which is very delicious - which has plums and berries. So this is my next famous chocolate that I'm going to work on.

Chris - Now when you say you designed the chocolate, do you mean you fiddled with the recipe, or you use some of your magic enzymes? In what way did you design it?

Ljiljana - So we do fiddle with the types of the chocolates, cocoa beans, that we take. We play a little bit around with a mixing of the chocolate with the ingredients. And if you want to get a soft, liquidy core in your chocolate, you actually use an enzyme.

Chris - Talk nicely to Ljiljana at the end, Joe; she might give you a bit of her famous chocolate bar.



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