Scientific reason behind why young children don’t like broccoli, experts find

Smelly gases, caused by enzymes in vegetables and saliva, could be to blame

Some adults also naturally dislike the taste but learn to tolerate it in the same way they do coffee and red wine, say scientists (iStock)

Unpleasant odours in the mouth could be to blame for children’s common dismissal of vegetables such as broccoli and cabbage, new research suggests, debunking the idea they are simply fussy eaters.

Researchers in Australia found enzymes from the brassica vegetable group, which also includes brussel sprouts, cauliflower and kale, can produce lingering smells when combined with bacteria in saliva.

Writing in the Journal of Agricultural and Food Chemistry, experts said parents and their children actually have similar levels of the odours, suggesting they share the same sort of microbiomes – bacteria – in the mouth.

But while children often refuse the vegetables, it appears adults learn to tolerate the odours over time.

“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 team of researchers, led by Damian Frank, wrote in the journal.

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

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.

Previous studies have shown adults to have varying levels of this enzyme in their saliva, but until now it was not known whether the same was true for children and if it influences their food preferences.

The team at CSIRO, Australia’s national science agency, went a step further and 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.

Explaining just how unpleasant its smell could be for youngsters, Dr Frank, a food and sensory scientist at the University of Sydney, told ABC: “Basically this gas is associated with the smells of farts and the smells of decomposing animals.”

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 findings, 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 said.