Brassica vegetables

Cruciferous vegetables include familiar leafy and flower-bud vegetables such as cabbage and broccoli. These vegetables are described as having sulfur-bearing compounds called glucosinolates as a characteristic component. When tissue is damaged, glucosinolates are broken down by enzymatic action, yielding products such as isothiocyanates. Review articles position glucosinolates and isothiocyanates as the causative substances of the characteristic pungent and bitter taste of cruciferous vegetables.

How much glucosinolate remains appears to depend more on the cooking method than on heat treatment itself. In research on broccoli, Brussels sprouts, cauliflower, and green cabbage, steaming, microwaving, and stir-frying showed no significant loss, whereas boiling caused a clear decrease; approximately 90% of the lost amount was detected in the boiling water. When finely chopped and left for 6 hours, as much as 75% loss has been reported. If the amount retained varies this much depending on cooking method, the flavor of raw and cooked forms cannot be described using the same measure.

Two glucosinolates, sinigrin and progoitrin, always correlate with the bitterness of Brussels sprouts themselves, while their relationship with preference is not uniform. Across 4 taste tests conducted between 1989 and 1995, a relationship in which higher combined content was associated with lower preference was observed only when the combined content of these two components exceeded 2.2 g/kg. In tests where content remained below this threshold, no relationship with preference was observed, though the correlation with bitterness continued across the full range of content. High content alone cannot be used as a straightforward measure of preference.

The view that genetic variation in TAS2R38, which influences bitter taste sensitivity, determines preference for cruciferous vegetables has often been discussed in review articles. However, research that has directly tested this view appears to show divided results. In a UK consumer study using rocket, the TAS2R38 genotype was related to bitter perception, but it was reported that it was the pungency of the leaves rather than bitterness that determined acceptance or rejection. In another study using cooked turnip, the TAS2R38 genotype had no significant effect on preference. A systematic review of bitter taste sensitivity and vegetable and legume consumption overall also found the association to be reported as very weak and not statistically significant. The simple scheme that people with stronger bitter perception avoid cruciferous vegetables is not supported, at least by these tests.