Posts by Bart Janssen
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Hard News: Science: it's complicated, in reply to Joe Wylie,
If you pick it once the faintest blush of colour shows there’s no detectable difference between leaving the fruit to fully ripen on the vine. It seems to be true, and I’m kind of curious as to why.
We don't know ... yet. Well we sort of know.
A lot of fruit undergo what is called a "climacteric" as they mature. It is a point when the fruit has pretty much finished all cell division and most of the cell expansion. We call that stage "mature green". It's really attractive for growers to harvest at mature green because the fruit are a bit firmer and don't get damaged in transport so easily.
Then at some point the fruit suddenly starts respiring very rapidly (breathing if you like, actually using oxygen and expelling CO2). At that time there is also a burst of ethylene, a gas that is produced by the plant and used as a signal by the plant. Once that ethylene production starts it is self amplifying.
It is the ethylene signal that starts up all the enzyme pathways that produce sugars from starches and also all the flavour and aroma compounds. Essentially it is the signal that the plant uses when the seeds are mature and the fruit is ready to be distributed and spread the seed with it. All the flavour and sugars and colour changes are there to attract whatever it is that spreads the seed around. In the case of apples it's bears!
Because the ethylene production is self amplifying if you pick the fruit after it has started it tends to continue by itself.
If you pick the fruit just after it is mature but before ethylene production has started then you can hold the fruit in an ethylene free environment and then give the fruit a burst of ethylene and ripening with continue as normal.
BUT
It's really hard to tell the difference between mature green and immature green. It's even harder for fruit that don't undergo any colour change on the tree eg avocado or kiwifruit. If you get it wrong by a lot no amount of ethylene will produce ripening. If you get it wrong by a little some of the ripening pathways will work eg colour development. But other pathways won't eg flavour. That's why you often see paler tasteless tomatoes in the supermarket. They were picked too early and will never ever ripen.
The really big question is what defines "mature green"? And we don't really know for sure. If we knew then maybe we could create some kind of test for it so growers knew when it was ok to harvest.
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Hard News: Science: it's complicated, in reply to Emma Hart,
And then they will remember that one shouldn’t ask questions one doesn’t want to know the answer to.
I can't be knowin' that!
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Hard News: Science: it's complicated, in reply to Steve Barnes,
Does leaving the tomato on a bit of disembodied vine help in the process of ripening?
Maybe. But the biggest thing is that the stalk has lots and lots of the compounds that smell of tomato. So for marketing purposes since they smell like tomatoes people will think they taste of tomatoes.
That said, some of the companies that sell tomatoes on the truss also vine ripen them.
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Hard News: Science: it's complicated, in reply to giovanni tiso,
In this respect the consumer contributes by being bloody stupid
Not entirely fair. The real problem is marketing. What happens is the producers ask a marketing firm to do a survey to find out which tomato the public prefer. Marketing company has lunch ... at Cibo. Then comes up with a survey consisting of a picture of two tomatoes and asks 100 people at the supermarket which picture of a tomato they prefer, then they have dinner ... at Clooney. Marketing company then writes a 29 page report on their survey, with pictures and a powerpoint presentation and has lunch ... at Euro. Marketing company then charges the producers $127ooo plus expenses. The producer having paid a shit load for the market report plant bright red round tomatoes. The supermarkets having also paid the marketing company for the same report will only stock the bright red round tomato.
Consumers when they complain they can't get nice tasting tomatoes are told that they are outliers and most of the public prefer the tasteless tomatoes ... and they did an expensive market survey to prove that.
Marketing executives stop at Sabato on the way home to pick up vine ripe tomatoes for dinner.
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Hard News: Science: it's complicated, in reply to Emma Hart,
drink nutrasweet
Ack phtooey!
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Hard News: Science: it's complicated, in reply to Ian Dalziel,
But where does it go?
Entropy?Well actually yes. Some of the key flavour compounds that people associate with tomato-y-ness are not very stable and degrade fairly quickly - becoming less complex chemicals i.e. entropy. They are only present in detectable concentrations if they are continually being produced - by enzymes that die at 4 C.
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Hard News: Science: it's complicated, in reply to Rich of Observationz,
One can argue that “taste” (as in food) is to a substantial degree a political/cultural construct though.
We have a sensory science team here where I work that do a lot of work teasing apart cultural preferences. In no small part because Japan is very important to the kiwifruit industry. They are starting to get numbers and statistics to test dogma about who likes what.
I guess for me as a scientist what is really exciting is the work that we (and others) are starting to make progress on concerning figuring out just which chemicals people can detect and how that varies from person to person and the correlating that with genotype. Even in the small studies we've done here we've found genes linked with the ability to detect important fruit flavour compounds. That sounds boring I guess but it is a really big step in starting to understand why some people like some foods.
The really interesting next step is to try and correlate the ability to detect a compound with whether you like the compound or a fruit containing the compound. It could go either way and certainly cultural experiences could play a big role as well.
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Hard News: Science: it's complicated, in reply to Joe Wylie,
What really bothered me about that piece is the casual suggestion that without GM assistance, flavour and yield are mutually exclusive. If he’s really working with stock that only set two useable fruit per plant then he’d appear to be on a hiding to nowhere.
Trust me the article is much more a failure of journalism than a representation of Steve Tanksley's ignorance. He really is very smart and has a deep knowledge of both the science and the industry.
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Hard News: Science: it's complicated, in reply to giovanni tiso,
Yeah, we so needed science to tell us that :-)
Yeah obvious answer is obvious. Although I wish our local fruit world understood that :(.
But to be fair it was quite interesting to find out exactly why the flavour disappears and never comes back.
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Hard News: Science: it's complicated, in reply to Joe Wylie,
Tanksley – and the article’s author
Knowing Steve I'd say the emphasis you are reading into the article is from the journalist not Steve himself.
Steve Tanksley's work is aimed at understanding what really contributes to the domestic tomato we know as compared to the wild progenitors. Once we understand how it works then you can make plans to improve varieties with some real confidence of success.