Making wild strawberry smells from fungi

Now, scientists are gearing up to swap skilled chemists for fungi in a lab in Germany! Well not quite, but they have stumbled on a strain of fungus that, when grown on certain forms of plant waste, can break down the waste into a suite of chemicals that smell just like wild strawberries. The rationale for this work is that, while shop-bought strawberries taste great, many people think wild strawberries taste even better, because they have a stronger, more floral aroma. But, sadly, wild strawberries are so small that it’s not viable to extract useful amounts of their flavour compounds from the fruits themselves. Instead this means we have to rely on artificial flavours, and this comes at a cost both financially and for the environment. Fungi, of course, work for nothing! Sally Le Page spoke with Holger Zorn from the University of Giessen to find out more...

Holger - Mushrooms are living in completely different environments. So they have the enzymes to break down almost each and every organic material. And that gives them the opportunity also to modify substances that are already present in the starting material to release pleasant or sometimes also unpleasant flavour compounds.

Sally - How did you test which fungi make the best smells?

Holger - We grew the fungi just on a plate, on the pomace of blackcurrant and we just smelled every day to see if a pleasant flavour developed or not.

Sally - So you're growing these fungi on this blackcurrant pulp. Where does that come from?

Holger - From the juice processing industry, just from blackcurrant juice production.

Sally - Why are you using that, of all the things you could be growing your fungi on?

Holger - It's a quite sustainable approach. This material is typically just discarded and of course we know that a number of potential potent flavour precursors are still present in the material. So in general, though it is currently discarded, it's a valuable material and we just want to make use of that.

Sally - So you're adding this library of fungi to this blackcurrant pulp. How did you work out which ones smell of wild strawberries? Is it just a matter of smelling them or is it a bit more high-tech than that?

Holger - The first step of course is just smelling. Our nose is by far the best instrument we have with us if we are talking about flavour compounds, and what we also have in our institute is a couple of well-experienced PhD students and post-docs that, in a panel, evaluate the flavours. For this fungus, all of them agreed that it's highly interesting and all of them said, 'oh, that's just like wild strawberry'. Of course, in the next step we use highly sophisticated analytical techniques, including gas chromatography, and also sniffing gas chromatography, which means that we have a human nose as a human detector coupled to a chemical machine.

Sally - You say 'a human nose'. This is attached to a human, so you have a person attached to the machine?

Holger - Yes. It's not detached from the human. The person is still behind the nose.

Sally - I just love the idea that the best way of detecting these compounds is still just to sniff them. I'm sure that in chemistry at school I was told not to go around sniffing random things in the lab.

Holger - Yeah. That's different in food chemistry. Of course we each and every time use our nose to detect interesting things in nature.

Sally - So you didn't set out to look for a wild strawberry smell. You were just like, 'let's put these fungi on this blackcurrant waste byproduct and see what happens.' And it just so happened that one of them was wild strawberries.

Holger - Exactly. That's just what happened. We didn't deliberately search for a wild strawberry flavour. That's just what came out.

Sally - Was it more than one fungus that made this smell or was it just the one particular one that happens to smell like strawberries?

Holger - We had several fungi that produced interesting and pleasant flavours, but this one, this Wolfiporia cocos was the only one that produced this wild strawberry type flavour.

Sally - And what does that fungus look like? What does it do in the wild?

Holger - In the wild, it lives in trees and it looks a bit like a coconut.

Sally - Does this coconut fungus smell like strawberries in the wild when it's growing on wood?

Holger - Not at all. It only smells like strawberry when you grow it on this blackcurrant pomace.

Sally - And what are the benefits of making flavours using fungi over the traditional chemical routes?

Holger - One benefit is that these types of flavours may be labelled as natural flavour compounds, as they are of course made by nature. So it makes sense to label them as natural. And the second aspect; the production of these bioflavours is much more sustainable than traditional chemical synthesis.