蘋果放得奈變軟?? (生物問題)

you have to look up and confirm with the following...

I think apple is resistance starch, i.e. the structure of these starch are digestable to human only when it is above certain temperature. Other example for resistance starch are potato and banana. (that's why cooked potato, banana or apple are much more desirable to human...) However, when you leave the fruit for long enough, the structure of the starch are broken down by it own emzyme and as a result, the molecule of these starch became smaller, hence the fruit become soft after a while.