Hate broccoli and cauliflower? Your microbiome could be partly to blame

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Enlarge / Many kids (and adults) don’t like broccoli, cauliflower, Brussels sprouts, and other types of cruciferous vegetables very much. Perception of taste is complicated, but our unique oral microbiomes could be one reason, according to a new study.

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For many people, nothing is less enticing than a large plate of steamed cruciferous vegetables at dinner. Yes, it’s supposed to be good for us, but that bitter taste is just too potent and unpleasant. This is especially true for young children, as any frustrated parent can attest. But an aversion to broccoli, cauliflower, and the like isn’t just a fussy person; some genetics are involved. And according to a recent article in the Journal of Agricultural and Food Chemistry, a person’s oral microbiome can also be a big factor.

In 1931, a chemist named Arthur L. Fox accidentally released the powdered form of phenylthiocarbamide (PTC) in his lab. He didn’t notice anything unusual, but his lab mate smelled a bitter taste. Subsequent experiments confirmed that this variation existed in the general population and that not being able to taste bitterness was a recessive genetic trait. For example, about 25% of the population cannot taste propylthiouracil (PROP), a chemical similar to bitter compounds found in cabbage, raw broccoli, coffee, tonic water, and dark beers. This population is, like Fox, essentially “blind to taste”.

There are 25 “bitterness” genes known to date; different bitter foods act through different receptors, and people may be high or low responders to one but not the other. Many scientists believe that those who can experience bitterness are likely reacting to compounds called glucosinolates, found in most cruciferous vegetables, such as broccoli, Brussels sprouts, and cauliflower. These glucosinolates are responsible for most of the nutritional benefits of these vegetables, but they also break down into pungent compounds that can negatively trigger the bitter taste receptors in many people. (I just happen to dislike all three, as well as raw tomatoes, and I refuse to feel bad about it.)

However, no gene could ever be responsible for our love or hate of specific foods. So many different compounds are related to flavor and aroma, not to mention texture (mouth feel), and all of them can contribute to how we enjoy or hate a food. And now we can add our oral microbiomes to the mix. While there is also a genetic component in the individual microbiome, according to Damian Frank from the recent article, this composition can change over the course of life. The environment therefore also plays a role.

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This latest study builds on the results of a 2018 study of raw cabbage, which found significant variability in the production of volatile sulfur compounds in saliva between individuals. Saliva keeps our mouths moist, fights germs and bad breath, and helps us chew and swallow food. And previous studies have provided evidence that saliva plays an important role in releasing flavor in food and therefore our perception of pleasure.

Broccoli and its cruciferous cousins ​​can produce an enzyme called S-methyl-cysteine-sulfoxide (SMCSO) when plant tissue is damaged, a kind of defense mechanism. Previous studies have shown that some people’s saliva contains high levels of a particular bacteria that can produce these sulfuric enzymes, which in turn could affect how people experience the flavors of cruciferous vegetables, among other foods. “This molecule has basically been ignored for a long time because it just isn’t that exciting,” Frank said.

Enlarge / Pray that this bitter-tasting plate of vegetables will magically disappear.

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Frank and his colleagues recruited 98 pairs of children (between 6 and 8 years old) and parents and made them chew on some wax paper to produce saliva for analysis, a task that proved difficult for many. In the end, 35 couples out of a total of 98 were able to produce enough saliva for this phase of the experiment, although all of them participated in the classification stages. These samples were then exposed to raw cauliflower powder and analyzed by proton transfer reaction mass spectrometry to measure individual differences in the production of volatile sulfur compounds in real time.

Next, the team presented the 98 participating parent / child pairs with “scent pens” containing various pure scent compounds diluted in propylene glycol, and asked them to rate the odors in terms of likeness and intensity. Children used an age-appropriate version of the “self-report dummy” to graphically record their ranking on a scale of 1 (frown) to 5 (smile). Adults used a different 9-point scale. The researchers used the same scales for the next step of the study, which was to test the taste of raw and steamed broccoli and cauliflower samples.

Gas chromatography

Frank et al. also used gas chromatography to identify the main odorous volatile compounds found in raw and steamed broccoli and cauliflower to see if the cooking process altered these profiles, completed by a group of trained experts. Dimethyl trisulfide (DMTS) was the most potent volatile in raw and steamed vegetables, producing “rotten, sulphurous and putrid” odors. Not surprisingly, not all participants liked this volatile – it’s also a “potent volatile component of rotting flesh,” according to the authors.

Other birds have added mustard or woody notes; radish and spicy earth; green and herbaceous notes; fungus or fungus; and floral or purple notes, depending on the vegetable. “In general, steaming was associated with a reduction in overall odor intensity in both vegetables, and no evidence of unique heat-generated odor compounds in cauliflower or broccoli was found. “, wrote the authors.

As with the 2018 study, there were large individual differences in the level of volatile sulfur production between the participants. Children whose saliva produced particularly high levels of volatile sulfuric compounds hated raw broccoli and cauliflower the most. This correlation was not found for the adults in the study, which the authors say may explain why some adults end up learning to tolerate the flavor as they age.

Additionally, “there was a significant relationship between children and parents in the amount of sulfur produced, which we assume is due to similar oral microbiomes,” Frank said. The authors point out that, while intriguing, this is a speculative find, as the team did not analyze what types of bacteria and how many of each type were present in the saliva samples. However, “other research groups have found significant relationships between the salivary microbiome of parents and children, especially mothers and children,” they wrote.

DOI: Journal of Agricultural and Food Chemistry, 2021. 10.1021 / acs.jafc.1c03889 (About DOIs).

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