Published: 29 September, 1999

Glucose sweetens fruits as it ripens

Why does fruit ripen?

When fruits ripen they undergo a series of changes that alter the way they look, feel, taste and smell. These changes are good because they make fruits more enjoyable to eat, they are softer and taste better. Unfortunately, the ripening process is difficult to stop and it lets fruits ripen too much and they spoil! Unripe fruits have a number of different acids and their sugars are bound in up a network or polymer that does not allow us to taste their sweetness. Starch is one type of network and it is composed of the simple sugar, glucose. Breaking down the starch and releasing the glucose makes fruits sweet. The acids in fruits are also changed and therefore the fruits are not tart. All of these reactions and more occur during ripening and contribute to the fruit becoming sweeter.

Fruit ripens by producing enzymes, or catalysts that breakdown the sugar polymers and also neutralize the acids. They know it is time to ripen because they produce an odorless colorless gas, ethylene, that triggers the production of enzymes. A number of years ago, scientists discovered this process and now use it to control the ripening of fruit by carefully controlling the storage atmosphere. So now we can enjoy fruit almost year round, rather than just around harvest. And because the ripening process can be controlled and halted, we can also enjoy fruit from around the world shipped by boats and trains to our neighborhood supermarket.