It is Christmas lunch and as you gaze around the table, everyone has a giant plate full of food. Moist turkey, golden roast potatoes, stuffing, cranberry sauce, fresh vegetables and…Brussels sprouts? Brussels sprouts look like innocent green balls but are a very divisive vegetable. No doubt you know people who have a pile of them on their dinner plate, and other people who go ‘eeewwww’ at the mere thought of sprouts. But why is this? Dr Ian Turner, Head of Forensic Science, investigates.
The history behind the sprout
Our story begins in 1931. A chemist called Arthur Fox was undertaking an experiment and accidently released a cloud of a compound called phenylthiocarbamide (PTC). One of Arthur’s fellow scientists working nearby complained that the cloud left a bitter taste in his mouth, but Arthur tasted nothing. Intrigued, he conducted a series of experiments to investigate further.
Arthur tested his family and friends and found that PTC tasted bitter to some and not to others – let’s hope they didn’t fall out with him if they could taste it! Moving forward in history, scientists have discovered that the ability to taste PTC is genetic. They have even identified the gene called TAS2R38. Your love or hate of sprouts can be blamed on your family tree. Studies in the 1970s discovered about 30% of people cannot taste sprouts’ bitter flavour. Lucky them!
You are probably beginning to wonder what this has got to do with Brussels sprouts? Well, they do not contain PTC. However, they do have compounds called glucosinolates which have a thiocyanate group (a mixture of nitrogen, sulphur and carbon) that is the same as PTC. It appears that there is a strong link between ability to detect PTC and the love, or not, of the infamous seasonal vegetable.
Interestingly, glucosinolates are also found in other vegetables like broccoli and cabbage. It is thought that they have a role in the plant, before it gets to the dinner table, acting as a defence system against disease and pests.
The sprout effect
Sprouts are notorious, not just for their taste, but also the unwanted side (or rear) effect they can cause: flatulence. Sprouts contain a sugar called raffinose which is broken down by an enzyme. However this enzyme is only present in our large intestine, the last part of the digestive tract. When raffinose is broken down a product of this is gas, specifically hydrogen, methane and carbon dioxide. So that is the gas, but what about the ‘delicate’ odour? Well, remember the thiocyanate groups containing sulphur that caused the bitter taste? These are turned into hydrogen sulphide by bacteria in the large intestine, which has a smell like rotten eggs.
However, sprouts are not all bad news. When glucosinolates are broken down in the body, they form isothiocyanates, amongst others things. The isothiocyanates also contain the thiocyanate group that cause that bitter flavour. One of the isothiocyanates is called sulforaphane, and a group of scientists in Italy have undertaken some basic research on its role as a protective agent against neurogenerative disease. Maybe there is a reason to eat sprouts after all?
Christmas cracker FACT
Brussels Sprouts first appeared in Europe in the 5th century, but were later cultivated near Brussels in Belgium, leading to their name. They are sometimes mistakenly called ‘Brussel’.