User-Friendly Onions

Ever wished you could curse the pesky chemicals responsible for making your eyes water when you slice into the flesh of an onion? Well, now you can with the knowledge that lachrymatory-factor synthase is the culprit, not the enzyme alliinase as previously thought. Alliinase is a vital component of a particular biochemical pathway within an onion which produces the compounds responsible for its distinctive flavour. It was thought that Alliinase also produced the irksome lachrymatory factor which stimulates tear production. Therefore scientists had believed that genetically engineering Alliinase-free onions would compromise the unique flavour that the onion contributes to many culinary dishes – despite allowing the human race to chop away in relative comfort.

The discovery of lachrymatory-factor synthase’s role in triggering eye-watering opens up the real possibility of a non-lachrymatory onion, created by down-regulating the synthase enzyme’s activity 1. So, next time you reach for an onion and brush away a tear, feel free to curse our new friend lachrymatory-factor synthase and look forward with anticipation to the day when Tesco stock no-more-tears onions.



  1. Imai, S., Tsuge, N., et al. 2002. Plant biochemistry: An onion enzyme that makes the eyes water. Nature.

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