Naked Science Forum
General Science => Question of the Week => Topic started by: thedoc on 11/05/2015 15:33:34
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Why are ripe pears juicer?
Asked by Dennis
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We answered this question on the show...
Unripe pears are dry, yet ripe pears are juicy so how do they become moist? Philip Garsed put Dennis' question to plant scientist Sonia Dunbar, [img float=right]/forum/copies/RTEmagicC_3526665467_25d4e329ff_o.jpg.jpg[/img]from Cambridge University...
Sonja - Fruit ripens to make it more appetising to creatures so that they will eat it and spread the seeds of the plant.
Philip - The animal gets a nice nutritious meal whilst the plant gets its seeds carried far away inside the animal before, of course, being deposited in some first class manure. Lovely, but what changes have to happen to our pear to change it to a lovely sweet and tasty fruit?
Sonja - The rest of the plant supplies the fruit with a sugar called sucrose. Some fruits like grapes break this down into two sugars called glucose and fructose. This is why fruits like grapes need to be left on the plant until they're fully ripe. Other fruits like our pear store the sucrose’s starch which is not very sweet. And they then break it down into glucose and fructose later on. That’s why a pear gets sweeter just sitting in a fruit bar.
Philip - But why does it get squishier as well?
Sonja - The texture of the fruit changes because of three enzymes called pectinase, cellulase, and lipase which together break down the fruit cells. Firstly, pectin is the material that helps glue the cells together. You might have used it to make jam. Pectinase unglues the cells. The second enzyme, cellulase breaks down a material called cellulose – the stuff that make cell walls stiff. Lastly, a third enzyme, lipase also lends a hand by breaking down the fats in the cell membrane. Combined, these enzymes make the fruit cells leakier and less tough. So the fruit is softer and juicier.