benzyl isothiocyanate

Horseradish (Armoracia rusticana, syn. Cochlearia armoracia) is a perennial plant of the Brassicaceae family (which also includes mustard, wasabi, broccoli, and cabbage). The plant is probably native to southeastern Europe and western Asia. It is now popular around the world. It grows up to 1.5 metres (5 feet) tall, and is cultivated primarily for its large, white, tapered root. The intact horseradish root has hardly any aroma. When cut or grated, however, enzymes from the now-broken plant cells break down sinigrin to produce allyl isothiocyanate, which irritates the mucous membranes of the sinuses and eyes. Once exposed to air (via grating) or heat, if not used immediately or mixed in vinegar, the grated mash darkens, loses its pungency, and becomes unpleasantly bitter-tasting.

Cress (Lepidium sativum), sometimes referred to as garden cress to distinguish it from similar plants also referred to as cress. Garden Cress is a rather fast-growing, edible herb. Garden cress is genetically related to watercress and mustard, sharing their peppery, tangy flavor and aroma. In some regions, garden cress is known as mustard and cress, garden pepper cress, pepper grass, pepperwort or poor person's pepper. This annual plant can reach a height of 60 cm (~24 inches), with many branches on the upper part. The white to pinkish flowers are only 2 mm (1/12 of an inch) across, clustered in branched racemes.