Plants contain a range of phytosterols. They act as a structural component in the Cell membrane, a role which in mammalian cells is played by Cholesterol.
The molecule shown on the right is β-sitosterol. By removing carbon 242, campesterol is obtained. By removing carbons 241 and 242, Cholesterol is obtained. Removing a hydrogen from carbons 22 and 23 yields stigmasterol (stigmasta-5,22-dien-3β-ol). Removing carbon 242 and hydrogens from carbons 22 and 23 yields brassicasterol (ergosta-5,22-dien-3β-ol). Further removal of hydrogens from carbons 7 and 8 from brassicasterol yields ergosterol (ergosta-5,7,22-trien-3β-ol). (Refer to the numbering of Steroid skeleton.)
Ergosterol plays a structural role as a sterol in the cell walls of fungi. The presence of ergosterol is one of the few significant differences that fungal cells have from animal cells, which are both eucaryotic. Antifungals often target ergosterol and its synthesis for this reason.
Presence of brassicasterol, together with auxiliary markers α-Linolenic acid and Erucic acid, is a marker of adulteration of soybean oil and sunflower oil with rapeseed oil. As there is no brassicasterol in sunflower and soybean oil, but its concentration in rapeseed oil is about 1400 mg/kg, the amount of rapeseed oil added can be calculated.
As a food additive, phytosterols have cholesterol-lowering properties (reducing cholesterol absorption in intestines), and may act in cancer prevention. Phytosterols naturally occur in small amount in vegetable oils, especially soybean oil. One such phytosterol complex, isolated from vegetable oil, is cholestatin, composed of campesterol, stigmasterol, and brassicasterol, and is marketed as a Dietary supplement.