Why tomatoes are less tasty

24 October 2016

Interview with 

Denise Tieman, University of Florida

TOMATOES

Tomatoes on the vine

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Are you of the opinion that supermarket fruits and vegetables just don't taste as good as the fare you can pick up in the local grocers? If so, science is on your side, because new research out this week in PNAS has shown that refrigerating tomatoes reduces their flavour. Graihagh Jackson caught up with the study's author, Denise Tieman...

Denise - Well, I've always loved tomatoes; as a child they were my favourite food. I started doing research in plant science and I soon fell into a lab that worked on tomato flavour.

Graihagh - Because your latest paper is all about keeping tomatoes tasty, but I wonder was there a moment when you were like - tomatoes just aren't as tasty as they used to be?

Denise - Yes, that was some of our previous research, actually, so we know that modern tomatoes don't taste as good as some of the older varieties - what we call Heirloom varieties. A lot of our previous research was trying to define what really makes a tomato taste good and we tested many, many varieties of tomatoes. We had people taste them and then we looked at the biochemistry of those tomatoes and tried to figure out what really would be the recipe for a perfect tomato.

Graihagh - Uhmm, and what did you find - what is the perfect recipe?

Denise - Well, it's a complicated mix of many things. The main components of a tomato flavour are sugar, acids, and aroma compounds and we find we that we need a base of sugars and acids but the aroma compounds are what really make a tomato a tomato.

Graihagh - And it's the chilling of tomatoes that dampens these aromas and you've been looking at how this is happening.

Denise - Yes, so they're often chilled by the supermarkets, by the producers, and well, it's been known that chilling tomatoes makes them taste bad. So what we did we looked at what was actually happening inside the tomato after the chilling.

Graihagh - And what was happening?

Denise - Basically, the sugar and acids I was talking about, they are not changed with chilling but you lose a lot of the aroma compounds, so the tomato tastes bland, it doesn't have that tomato flavour. And so what we did was we looked at looked at what was actually happening at a genetic level and we found that with extensive chilling (about a week of chilling), the genes that make these aroma compounds are shut off.

Graihagh - These genes are responsible for making enzymes which, in turn, synthesise something called "volatile chemicals" - to you and me that's just tasty aromas. And when they're chilled the mechanism used by cells to control genes are turned off - in this case it seems forever!

Denise - They don't recover; they won't be turned back on again if you bring it back to room temperature.

Graihagh - There's a trade off then and I suppose many might choose to eat bland tomatoes and reduce food waste, especially given that most of us never normally eat them on their own. Which begs the question, does this finding really matter or is there something else going on here? For instance, could taste indicate the levels of nutrients within a tomato?

Denise - Well, that's another thing you know, and there's been some theories as far as that's concerned. A lot of these aroma compounds are actually kind of cues for different nutritional compounds. For instance, they come from carotenoids like lycopene and beta carotene that everybody tells us is good for us now, and some of them come from amino acids which we also need, and some of them of them come from lipids which we need. So a lot of them do seem to come from compounds that are actually very nutritious for us.

Graihagh - So it could be the case, and I suppose this might apply to other fruits as well that supermarkets are chilling?

Denise - Yes. Tomatoes are especially susceptible to chilling injury but other fruits and vegetables also are. Maybe not to quite the extent the way the lose so much flavour as tomatoes, but they do see the same thing happening with other fruits and vegetables.

Graihagh - Now that you sort of know on a genetic level what's going on, does that mean we can somehow use this and have tasty tomatoes that also last a sufficient amount of time?

Denise - Well that's what we hope. Now that we actually know what's happened, maybe we can find tomatoes, older varieties of tomatoes, that might be less susceptible to this chilling. And so, if we can find those, then we can go back and breed those traits into the modern tomatoes and, hopefully, prevent some of this loss of flavour with chilling.

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