These enzymes, called cysteine lyases, are produced by different kinds of bacteria that live in the mouth. The same enzymes are also locked away in the cells of Brassica vegetables, such as cabbage, Brussels sprouts, broccoli and cauliflower. So when we chomp into a broccoli floret, these enzymes spill out of their storage containers in the veggie's component cells while those in our spit kick into gear.
These enzymes break down a compound called S-methyl-L-cysteine sulfoxide (SMCSO) in cruciferous vegetables, and this breakdown process transforms the compound into pungent odor molecules. Previous studies of adults suggest that the level of cysteine lyase activity in a person's spit determines how much the SMCSO breaks down, and therefore, how many stinky molecules get produced in the process. This, in turn, influences how cruciferous veggies taste to adults.