From fresh clementines to buddha's hand and deliciously tart lemons, citrus fruits have long been known for the acidic punch they add to many of our favorite recipes—and for being delightfully sour. But it wasn't until now that scientists truly understood how fruits under the citrus umbrella differed from all other fruits, and exactly where their sour profile came from.
In late February, researchers at the University of California Riverside published new materials in the journal Nature Communications that highlights exactly where citrus fruits' flavors come from. Apparently, it all comes down to the fruits' genetics—experts analyzed citrus fruit flesh and found that hydrogen levels are directly tied to how sour any fruit will taste. Scientists discovered that pulp from sour fruit contains more hydrogen ions, which leads to a lower pH level overall, and the tangy profile that our taste buds recognize as sour. But sweeter fruit—like pineapples or papayas—has pulp that contains fewer hydrogen ions, leading to less of an acidic profile.
This research is the latest among a body of previous work that suggests other genes, known as CitPH1 and CitPH5, are largely responsible for sour flavor profiles in fruit. Ronald Koes, a researcher at the University of Amsterdam in the Netherlands, discovered the connection when his team analyzed the Faris variety of a lemon tree, which produces both sweet and sour lemons.
The joint research between Amsterdam and UC Riverside suggests that these two genes produce proteins that increase the amount of hydrogen ions within the fruit's cells, thus leading to a more acidic fruit overall. The new information may be very useful to fruit breeders, who can target these genes and aim to reduce hydrogen levels in their fruits overall, researchers said. In the near future, altering hydrogen levels could help farmers grow traditionally sour fruits with a newfound sweetness—without completely stripping it of all of its signature tartness.