Esterification
Esterification is the transformation of an acid in the fruit into an ester(alkali). Ester  is responsible for the fragrance and flavor of fruits and flowers. Once the transformation to an ester is complete the fruit has more flavor and fragrence which we recognize as characteristics of ripe fruit.
http://www.plantcell.org/cgi/content/full/12/5/647/f1
This diagram shows the general scheme for the esterification reaction.
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