We now know what makes oranges taste of oranges

Chemical analysis has revealed 26 compounds responsible for the distinctive flavour of oranges. The findings will help plant scientists create disease-resistant orange hybrids that taste just as good as the original.

In recent decades, citrus greening disease, also known as huanglongbing, has devastated the production of citrus fruits around the world. Oranges (Citrus sinensis) have been particularly affected by the disease, says Anne Plotto at the US Horticultural Research Laboratory in Florida.

Plotto and her colleagues wanted to see if it was possible to create hybrids that are tolerant to citrus greening disease while preserving the signature flavour of oranges.

To identify the chemicals responsible for this flavour, the researchers analysed 179 juice samples from a range of citruses, including oranges, mandarins (Citrus reticulata), trifoliate oranges (Citrus trifoliata) and their hybrids. Trained citrus testers also tried each sample and rated how much it tasted like orange juice.

They found that the juices with the strongest orange flavour all contained 26 specific compounds. Seven of these compounds are a type of chemical called esters, which seemed to be the key to distinguishing the taste of oranges and mandarins.

Plotto and her team then conducted a genetic analysis of the fruits and found a gene responsible for the synthesis of all seven esters, which they dubbed C. sinensis alcohol acyltransferase 1.

“This gene is expressed much more in the cultivars that produce a lot of esters,” says team member Zhen Fan at the University of Florida.

The research could ultimately help to achieve disease-tolerant hybrids with a rich orange flavour, says Plotto. “The findings could be used to screen citrus hybrid seedlings for desired orange flavour at an early stage, instead of waiting 10 to 15 years for the tree to bear fruits,” she says.