The tartness of fruits and vegetables is due to:

The correct response involves understanding the compounds associated with the flavors of fruits and vegetables. Tannins are polyphenolic compounds found in many plants and are responsible for astringency and tartness in various fruits. These compounds can contribute a sour or bitter flavor to certain fruits and vegetables, enhancing the overall taste profile, particularly in unripe fruits.

Flavones, chlorophyll, and anthoxanthins have different roles and characteristics. Flavones are a type of flavonoid and are more associated with coloration rather than tartness. Chlorophyll is the green pigment in plants responsible for photosynthesis, but it does not contribute to the tart flavor. Anthoxanthins also influence the color of fruits and vegetables—offering a range of white to yellow hues—yet they are not primarily related to the tartness experienced in taste.

Tannins are thus correctly identified as the compounds that impart a level of tartness, which helps to explain the flavor of many varieties of fruits and vegetables.