Citrus fruits have always been known for their sour, zesty taste. With a
little help from science, researches have finally identified what gives the
lemon, orange, grapefruit, and other similar fruits their particular tangy
flavor.

Scientists from the University of Amsterdam found out that the sour taste of
citrus fruits is due to the acidity in the vacuoles of the citrus' fruit
cells. Vacuoles are the compartments of the cell that are filled with fluid
that the cell needs to survive. In the case of the citrus fruit, it was
found that the citrus' vacuole fluid is extremely acidic due to CitPH1 and
CitPH5 genes. These genes are not only responsible for the acidity of the
cell vacuoles, but for the determination of the flower color as well.
Results showed that citrus plants express more CitPH1 and CitPH5 compared to
other sweet fruit varieties. Thus, the citrus produces more sour-flavored
fruit. These findings can support future studies that may be able to
determine just how sweet or sour we want our fruits to be.

[www.nature.com]