Does the nutrition of a fruit or vegetable depend on how ripe it is?
-- Claire Snyder
An apparently simple question with a semi-complex answer.
Some fruits and vegetables offer different nutrition profiles depending on what stage of ripeness they are at.
Sun-ripened vine tomatoes, for example, are ideal because they produce plenty of antioxidants and polyphenols while fully ripening, thanks to the sun's rays.
Conventional tomatoes, however, are picked when they are still green. Days later, they arrive at your supermarket.
In between being picked and going up for sale, they (as well as avocados, pineapples, and apples, among other fruits) are sprayed with ethylene, a plant hormone that speeds up the ripening process.
It's not so much that ethylene is harmful as much as this artificial ripening process does not allow the fruit to provide as much nutrition as it could.
Some of the chemical processes that occur as a result of exposure to ultraviolet light do not take place. In turn, some enzymes are not present in that tomato.
By the way, this is why often times a great-looking tomato is tasteless. Some of the enzymes a tomato produces as a result of exposure to the sun greatly affect its taste!
This is one big reason why buying local and sesonal produce is recommended.
Not only is it an easier load on the environment, it also increases your chances of buying produce that has been ripened by nature, in turn providing more nutrition.
This is not to say conventional tomatoes are "unhealthy" or "bad for you." However, you are definitely sacrificing some nutrition for convenience.
Assuming you are eating naturally ripened food, though, once it's okay for consumption (its texture and taste are palatable), its nutritional profile stays the same for a few days.
Tuesday's ripened banana will offer the same amount of potassium, Vitamin C, and Vitamin B6 on Thursday.
Before any glycemic index fans jump down my throat: yes, the glycemic index of that banana increases slightly as it ripens, but not significantly.