Getting children to eat their greens is a battle as old as time, and every parent has their own way of getting vegetables into a protesting child. 

But a new study has found that the vocal objections to vegetables from children worldwide is not merely petulant behaviour, but a natural consequence of biology.

A chemical in brassica crops – which includes broccoli, kale, cauliflower, cabbage, turnip and Brussels sprouts – mixes with enzymes in saliva and this produces sulphurous compounds that taste deeply unpleasant. 

The chemical in question is S-methyl-ʟ-cysteine sulfoxide which, on its own, is nondescript. However, it becomes unpleasant when broken down by naturally occurring enzymes found in our oral microbiome – the “good” bacteria that exists in our mouths. 

However, not everyone possesses the same concentration or recipe of enzymes in their oral microbiome, with some people naturally making a lot, and others producing very little. 

For people who naturally have lots of these sulphur-producing enzymes, the pungent taste of brassica crops is more intense, and these individuals are therefore more likely to shun Brussels sprouts at the Christmas table and avoid kale smoothies. 

Is a dislike of vegetables hereditary?

This relationship has long been known, but researchers at the Commonwealth Scientific and Industrial Research Organisation, an Australian government agency responsible for scientific research, investigated if there was any hereditary aspect to enzyme production, and therefore, if a dislike of vegetables runs in the family, and is passed on from parent to child. 

To do this, researchers took raw and steamed broccoli and cauliflower and ran it through an analytical process called gas chromatography-olfactometry-mass spectrometry.

This process captures vapour given off by the vegetables and pulls it apart into its component parts to precisely determine what compounds are present and how much of them there are.  

Then, 98 pairs of parents and children were asked to smell the specific compounds and rate them on how much they liked or disliked them. One of the compounds, dimethyl trisulfide, which smells sulfurous and putrid, was unsurprisingly found to be the least liked odour by children and adults alike. 

Saliva mixed with raw cauliflower powder

Researchers then collected saliva samples from the children, aged between six and eight, and their parents and mixed this with raw cauliflower powder.

These concoctions were designed to mimic the reactions of when a person chews their food and the produced compounds and scents were then also run through the same analytical technique.

Researchers found there to be a large range in the level of sulphur compounds produced which depended on the amount of enzyme they naturally possess. 

Children were found to have similar levels of sulphur to their parents, indicating the palate for vegetables, positive or negative, is passed down from one generation to the next.

Yet, only in the children did high sulphur compound concentration lead to a noticeable dislike of brassica vegetables. 

Parents of these children, although they had the same oral microbiome make-up as their offspring and the same high sulphur levels, did not report a strong dislike of the vegetables. 

Learning to tolerate potent scents

Researchers say this may be due to them learning to tolerate the scent over time, and growing to accept and embrace the potent flavour. 

“Interactions between brassica vegetables and human saliva can affect in-mouth odour development, which in turn may be linked to individual perception and liking,” the researchers write in their paper, published in the Journal of Agricultural and Food Chemistry.

“It is an intriguing finding that there was a significant relationship between related adult/child pairs.

“Other research groups have found significant relationships between the salivary microbiome of parents and children, especially mothers and children.”

The results provide a new potential explanation for why some people like the vegetables and others, especially children, do not, the researchers say.