Scientists Identify Gene Responsible for Olive Oil’s Aroma

Researchers determined that manipulating the 13-HPL gene could allow farmers to predict olive oil aroma or create new cultivars with specific aromas.

A team of Spanish researchers has investigated a key genetic trait of the olive tree and devised a way to manipulate the associated gene’s expression with relevant consequences on olive oil aroma.

The discovery may allow growers to select cultivars to produce olive oils with specific aromas or researchers to breed new cultivars with pre-determined aromas. Genetically modified olives could feature a more fruity or pungent aroma.

“Plants produce and emit a huge diversity of volatile organic compounds, which are released from different tissues such as leaves, fruits, flowers and roots,” the researchers wrote. “From a chemical point of view, these plant volatiles are organic lipophilic molecules characterized by low boiling points and high vapor pressures at ambient temperatures.”

Volatile compounds are molecules that, once released by their source, reach the olfactory receptors and create the aroma.

The 13-HPL gene has been investigated for decades as it plays a pivotal role in the synthesis of the main volatile compounds that make up the aroma of virgin olive oils.

“It was not until approximately a decade ago that we were able to isolate and characterize the 13-HPL gene from the olive tree, as well as to demonstrate the putative [commonly thought] functionality of the protein it encodes, the 13-HPL enzyme,” Carlos Sanz, the leader of the biochemistry and plant food technology research group at the Spanish National Research Council’s Fat Institute, told Olive Oil Times.

The 13-HPL is an enzyme that produces the six-carbon C6 aliphatic aldehydes hexanal or hexenals from polyunsaturated fatty acids with a hydroperoxide group at carbon 13.

These volatile aldehydes, and their alcohol and ester derivatives, are components of the aroma of the fruits of different plant species. In olives, they are also responsible for the smell of cut grass that is produced when the plant leaves are crushed.

“The 13-HPL is an enzyme that is part of the lipoxygenase pathway, which is a highly conserved biochemical pathway in plants that functions in different plant organs,” Sanz said. “We have verified in previous studies that the profile of volatile compounds obtained after crushing the olive leaf is basically the same as that obtained after crushing the olive fruit since, in both organs, the damage to the tissue triggers the functioning of the lipoxygenase pathway and consequently the synthesis of volatile compounds.”

“This is essentially the origin of the aroma of virgin olive oil,” he added. “This aroma is only produced when the integrity of the olive fruit is destroyed in the milling stage of the virgin olive oil extraction process.”

The study also found that there is only a single 13-HPL gene in the olive, unlike in other metabolic steps in synthesizing these volatile compounds, in which a considerable number of genes with the same function may be involved.

“Well, once the gene had been identified and characterized, the next step was to determine its functionality in vivo, that is, to verify that this gene is expressed in the olive to produce 13-HPL and that this enzyme works as it does in vitro,” Sanz said. More