Proof that scientists know their onions

Scientists have identified the enzyme that is responsible for cooks shedding tears while chopping onions and think that a genetically modified version could save the flavour but stem the weeping.

Scientists have identified the enzyme that is responsible for cooks shedding tears while chopping onions and think that a genetically modified version could save the flavour but stem the weeping.

Previously, evidence suggested that the chemical making us weep, sulphenic acid – which is then converted to the irritant sulphuric acid once it reacts with the water in the eyes – was linked to the chemicals giving the root its flavour.

But Japanese scientists found that an enzyme called lachrymatory-factor synthase was specifically responsible for the tear-producing element but not the flavour. The findings are reported today in the science journal Nature.

They wrote: "It might be possible to develop a non-lachrymatory onion by suppressing the lachrymatoryfactor synthase gene while increasing the yield of thiosulphinate. Thiosulphinate is responsible for the flavour of fresh onion."

Such an onion, genetically modified not to produce the enzyme, should taste as good as the original.

For those unprepared to wait, there are still a couple of methods to hand.

One is to chop the onion next to a low-burning gas flame: this attracts the potentially irritant vapours towards the flame. The other is to put the onion in the freezer for 15 minutes before cutting it: this reduces the volatility of the irritants so they are less likely to reach the eyes.