The aroma and flavor of coffee depend on different chemical compounds

Coffee’s characteristics relate not only to caffeine but also to substances belonging to a class of compounds that confer the flavor of mint and the aroma of sandalwood, according to researchers from Brazil and France.

By Elton Alisson  |  Agência FAPESP – Coffee’s aroma and flavor depend not only on caffeine but also on a number of other chemical compounds found in different parts of the plant, in addition to coffee beans.

A group of Brazilian researchers at the Paraná Institute of Agronomy (IAPAR), in collaboration with colleagues at the University of Londrina, the University of Western São Paulo (UNOESTE) and São Paulo State University (UNESP) in Rio Claro, as well as the Brazilian Agricultural Research Corporation (EMBRAPA Coffee) and France’s Agricultural Research Center for International Cooperation & Development (CIRAD), measured levels of two of these compounds, kahweol and cafestol, in the leaves, roots, flowers, and fruits of one variety of Coffea arabica. 

The results of the study were published in the journal Plant Physiology and Biochemistry and highlighted by Science.

“It’s the first time anyone has quantified these two compounds, which we believe to be linked to aroma and flavor in other organs of the plant, apart from the bean,” said Douglas Silva Domingues, a professor in UNESP Rio Claro’s Botany Department and one of the authors of the study. Domingues is the principal investigator of a research project on C. arabica supported by a Young Investigator Grant from FAPESP. 

“Now that we have information about which organs of the plant can produce these compounds, we plan to compare their production in different varieties of arabica and identify the genes responsible for producing them,” Domingues said.

Kahweol and cafestol are not only lipids, he added, but also terpenoids, which are chemical compounds that confer the flavor of mint and the aroma of sandalwood, for example. 

Produced by different parts of the coffee plant to repel herbivorous insects or to attract pollinators, these two substances are found at high concentrations in coffee essential oil.

Research performed in the 1980s revealed the anti-oxidant properties of these compounds, encouraging their use by the cosmetics industry, and anti-tumoral properties discovered in the 1990s aroused the interest of pharmaceutical companies. 

However, studies carried out by researchers in chemistry and food engineering to quantify these substances in the coffee plant focused on the beans, in which the levels vary between 10% and 15%, according to Domingues.

“Because these two compounds account for such a significant proportion of the coffee bean, and because substances in the same chemical class confer the minty flavor and the sandalwood aroma, we decided to quantify them in other parts of the plant,” he said.

Unequal levels

The researchers measured levels of kahweol and cafestol in the leaves, roots, flowers, and fruits of a variety of C. arabica at seven stages of development (between 30 and 240 days after flowering) using high-performance liquid chromatography (HPLC), an analytical chemistry technique that separates, identifies, and quantifies the components of a solution.

The results of their analysis showed that kahweol predominates in the roots and cafestol in the flower buds. Levels of both substances increased in the fruits during their development, peaking at 120 days after flowering. Neither kahweol nor cafestol was detected in the leaves.

“One hypothesis that could explain the presence of these compounds in some parts of the plant and not in others is that they repel insects and attract pollinators, among other functions, so it may be more interesting for the plant to use them against organisms that interact with their fruits and roots than to repel insects that attack their leaves,” Domingues said.

The researchers do not yet know whether the compounds are found at different levels in different parts of all arabica plants, as they analyzed only one variety, but now that they know which organs of the plant can produce the substances, they plan to compare production across several different varieties.

“Based on our finding that levels of kahweol in the roots are similar to levels in the fruits, as part of the project supported by FAPESP, we can now compare the patterns of gene activity in these two parts of the plant to try to find out which genes relate to the production of kahweol and which to cafestol,” Domingues said.

To do so, the researchers plan to sequence the transcriptomes of two varieties with different breeding histories in order to see which genes are present in different plant tissues.

The idea is to use network interference, a technique used by Facebook to detect which subjects interest an individual and who his or her closest friends are, for example. 

“If we know a gene isn’t active in leaves but is active in roots and other parts of the plant, by inference, we can test the hypothesis that it’s responsible for the production of kahweol and cafestol,” Domingues explained.

The priority now is to understand the genetics of arabica and the molecular reasons for the differences in the levels of kahweol and cafestol in different parts of the plant, according to Domingues, who belongs to an international consortium that is sequencing the C. arabica genome.

Later, the researchers intend to use this knowledge to enhance the plant’s resistance, assist its genetic improvement, and produce the compounds via biotechnology strategies, he added.

“Today, it’s possible to produce mint aroma using biotechnology strategies. If we know which genes are responsible for producing kahweol and cafestol, we’ll be able to use the same strategies to produce the compounds in the lab,” Domingues said.

The article “Diterpenes biochemical profile and transcriptional analysis of cytochrome P450s genes in leaves, roots, flowers, and during Coffea arabica L. fruit development” (doi: 10.1016/j.plaphy.2016.12.004), by Domingues et al., published in the journal Plant Physiology and Biochemistry, can be retrieved from sciencedirect.com/science/article/pii/S0981942816304624.