Glucosinolates & Sulforaphane: Cruciferous Vegetable Chemistry

Glucosinolates are sulfur-containing compounds found in cruciferous vegetables (broccoli, cabbage, kale, cauliflower, brussels sprouts, radishes, watercress). On their own, glucosinolates are biologically inactive. The magic happens when plant cells are damaged (by chopping, chewing, or crushing), releasing the enzyme myrosinase, which converts glucosinolates into biologically active isothiocyanates — the most studied being sulforaphane.

The Myrosinase Factor

Myrosinase is heat-sensitive. Heavy cooking (boiling, microwaving at high power) destroys myrosinase, preventing the conversion of glucosinolates to sulforaphane. Strategies to preserve or restore myrosinase include: lightly steaming (2-3 minutes), adding raw cruciferous vegetables to cooked ones, chewing raw broccoli sprouts, or adding a source of myrosinase (like mustard seed powder) after cooking.

Glucosinolate compounds also overlap with the goitrogen category — some glucosinolate metabolites can interfere with iodine uptake in the thyroid, though this is primarily a concern at very high intakes or in the context of iodine deficiency.

For the xenohormesis perspective on why these plant defense compounds benefit humans, see the Plant Stress Compounds page.

External resources: Linus Pauling Institute — Isothiocyanates