Why children turn their noses up at broccoli and Brussels sprouts may be down to bacteria in their mouths, a new study suggests.
Rather than just being fussy eaters, research indicates there could be a scientific reason for youngsters, and adults, disliking a group of vegetables known as brassica vegetables, which also include cauliflower, kale and cabbage.
Enzymes from these vegetables and from bacteria in saliva can produce unpleasant odours in the mouth.
But while children often refuse the vegetables, it appears adults can learn to tolerate the odours over time.
Damian Frank and colleagues conducted the research at CSIRO, Australia’s national science agency.
Writing in the Journal of Agricultural and Food Chemistry, the researchers found that parents and their children have similar levels of the odours, suggesting they share the same sort of microbiomes – bacteria – in the mouth.
They also found that high levels cause children to dislike the vegetables.
“Interactions between brassica vegetables and human saliva can affect in-mouth odour development, which in turn may be linked to individual perception and liking,” they said.
“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.”
According to scientists, brassica vegetables contain a compound called S-methyl-L-cysteine sulfoxide that produces potent, sulphurous odours when acted upon by an enzyme in the plant.
This is also the case for the same enzyme produced by bacteria in some people’s oral bacteria.
While previous studies have shown adults have varying levels of this enzyme in their saliva, it was not known whether this is true for children and if it influences their food preferences.
In the study researchers identified the main compounds in raw and steamed cauliflower and broccoli that produce the odour.
They then asked 98 child and parent pairs, with children aged between six and eight, to rate the key odour compounds.
Both children and adults least liked dimethyl trisulfide, which smells rotten, sulphurous and putrid.
The team then mixed saliva samples with raw cauliflower powder and analysed the types of compounds produced over time.
They found large differences between individuals, but that children usually had similar levels as their parents, which the researchers suggest is likely explained by similar microbiomes.
According to the study, children whose saliva produced high amounts of sulphur compounds disliked raw brassica vegetables the most, but this relationship was not seen in adults, who might learn to tolerate the flavour over time.
The results provide a new potential explanation for why some people like the vegetables and others, especially children, do not, the researchers say.