by Catherine Peyrot des Gachons
Researchers have been investigating the potential health-promoting properties of extra virgin olive oil (EVOO) for decades, including its possible medicinal value for preventing cancer, Alzheimer’s, and cardiovascular disease, as part of the well-known Mediterranean diet. When consumed in liquid form, some EVOOs taste bitter and evoke an irritation primarily sensed in the throat, which may trigger throat clearing and cough. Those sensory traits are valued by connoisseurs as a sign of high quality, notably for oil freshness and extended shelf life, but when general consumers undergo preference tests between various olive oils, they most frequently select the oils with low bitterness and pungency. This can lead to a missed opportunity because EVOO’s bitter taste and throat pungency are caused by the presence of phenolic compounds, the very ones believed to be the main contributors to EVOO health benefits (1)
The concomitant perception of both sensations, when it occurs, reflects the simultaneous presence of different phenolic compounds, some of which are perceived as bitter such as oleuropein or apigenin and, one primarily, oleocanthal that is perceived as pungent in the throat. Bitter tasting compounds bind to a specific and large set of taste receptors, the TAS2Rs (25 members in humans)(2). Whereas, oleocanthal evokes throat pungency via activation of TRPA1 (3), an ion channel belonging to the TRP family, of which several members are receptors conveying the sensations of pain from very hot water or irritation from spices. A lack of bitterness or pungency in an EVOO generally signifies the absence of the mentioned phenolic compounds. However, what is interesting to note, is that many EVOO users seem unaware of the fact that EVOOs can even be irritating. Although, there are many possible explanations for this unawareness, one is that EVOOs consumed in foods may not provoke the same level of throat irritation as they do when consumed alone. To confirm that assumption and demonstrate what might happen, we designed a series of experiments.
We first asked participants to evaluate the throat pungency and bitterness intensity of pure oils, presented in liquid form and three model mayonnaises made with the corresponding oils, a small amount of water and egg yolk. None of the additional ingredients often used in traditional mayonnaise recipes such as salt or lemon were used in our samples in order to limit gustatory stimulations other than those evoked by the oils. The first oil, a non-EVOO oil (HO), was a tasteless high oleic acid safflower oil, chosen to be the best match to EVOO regarding its lipid composition. The second oil (LOC) was an EVOO containing a low amount of oleocanthal and 200 mg/kg total phenols, and the third oil (HOC) was an EVOO containing a high amount of oleocanthal and 520 mg/kg total phenols. In the figure below, we see how an EVOO high in oleocanthal and total polyphenols like the HOC oil, is perceived as much more pungent and bitter than the other oils. Strikingly, when HOC is tested as a model mayonnaise, its strong pungency almost entirely vanishes. This mayonnaise was made of 90% oil and thus dilution cannot be responsible for the large loss in pungency intensity relative to the pure HOC oil. The observed pungency suppression most likely reflects the fact that oleocanthal is no longer able to activate the TRPA1 receptors through which the sensation is mediated. Similarly, perceived bitterness of the HOC mayonnaise decreases markedly, although to a lesser extent.
In subsequent experiments, we showed that the proteins in the egg yolk were responsible for eliminating EVOO pungency and bitterness. Other proteins such as whey proteins yielded similar sensory suppression. The sensory loss was dose dependent: the more proteins added, the larger the reduction in pungency and bitterness (see article 4). These results support the hypothesis that the presence of food proteins in the mixture triggers sensory reduction due to interaction between the proteins and both oleocanthal (throat pungency inducing) and bitter tasting EVOO compounds.
In addition to the implications these results have for sensory and culinary aspects of EVOO use, they raise important questions about the bioavailability and bioactivity of potentially healthful EVOO phenolics when consumed with many foods. Can this interaction with certain proteins reduce the compounds medicinal effects in the human body by obstructing the activation of some targets? Or, to the contrary, might it make them more available in the human body by protecting them against degradation? We don’t know the answer to those questions yet but it is important to take the protein binding factor into consideration in EVOO phenolic studies. In our lab, we have a particular interest to understand the pungent compound oleocanthal, which is believed to be a potent anti-inflammatory agent (5) with high preventive and/or therapeutic potential for several human illnesses such as certain cancers, neurodegenerative diseases and rheumatic disease (6).
Knowing definitively that EVOO can be comfortably consumed when mixed with other foods might encourage people to consume more of it, and even seek EVOOs high in polyphenols, thereby gaining from its medicinal and culinary benefits.
Read all at: Peyrot des Gachons, C., O’Keefe, A.J., Slade, L. et al. Protein suppresses both bitterness and oleocanthal-elicited pungency of extra virgin olive oil. Sci Rep 11, 11851 (2021). https://doi.org/10.1038/s41598-021-91046-0
Catherine Peyrot des Gachons, PhD
Senior Research Associate
Monell Chemical Senses Center,
Philadelphia, Pennsylvania, USA
Ph.D, University of Bordeaux, awarded in Dec 2000. Dissertation: Research on the aromatic potential of Vitis vinifera L.cv. Sauvignon Blanc grapes (Dr. Denis Dubourdieu, Advisor).
Adjunct faculty in the Food Sciences Program at Drexel University, Philadelphia, PA. (Course on Wine Sciences).
Catherine Peyrot des Gachons’ research focuses on human oral perception and its implications in nutrition and health. Through the study of based-plant products like wine, olive oil, tea and spices she is studying olfaction, taste and somatosensation, such as irritation, astringency and mouthfeel. She is also looking at the beneficial impact those products have on inflammation-related diseases.
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- Peyrot des Gachons, C. et al. Unusual pungency from extra-virgin olive oil is attributable to restricted spatial expression of the receptor of oleocanthal. J. Neurosci. 31, 999–1009 (2011).
- Peyrot des Gachons, C., O’Keefe, A. J., Slade, L. & Beauchamp, G. K. Protein suppresses both bitterness and oleocanthal-elicited pungency of extra virgin olive oil. Sci. Rep. 11, (2021).
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