Phytosterols (also called plant sterols) are a group of steroid alcohol, phytochemicals naturally occurring in plants. They are white powders with mild, characteristic odor, insoluble in water and soluble in alcohols. They have many applications as food additives, and in medicine and cosmetics.
- The molecule shown at the top of the page 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).
Detection of organic matter
Due to its presence in terrestrial plant matter and only rare occurrence in unicellar algae, β-sitosterol can be used as a biomarker indicating the amount of terrestrially derived organic matter present in a sample. As these sterols are generally insoluble in water, they will partition onto suspended or settled solid matter (e.g. sediments). Due to grain surface area effects, muds will have greater concentrations by weight than sands or coarser grained sediments. To overcome this effect, ratios of individual sterols to total sterol content or cholesterol are usually used to indicate organic matter source.
Detection of adulteration
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 ingredient or additive, phytosterols have cholesterol-lowering properties (reducing cholesterol absorption in intestines), and may act in cancer prevention. Phytosterols occur naturally in small quantities in vegetable oils, especially sea buckthorn oil (1640mg/100g oil), corn oil (968mg/100g), and soybean oil (327mg/100g oil). One such phytosterol complex, isolated from vegetable oil, is cholestatin, composed of campesterol, stigmasterol, and brassicasterol, and is marketed as a dietary supplement. Sterols can reduce cholesterol in human subjects by up to 15%.
The mechanism behind phytosterols and the lowering of cholesterol occurs as follows: the incorporation of cholesterol into micelles in the gastrointestinal tract is inhibited, decreasing the overall amount of cholesterol absorbed. This may in turn help to control body total cholesterol levels, as well as modify HDL, LDL and TAG levels. Many margarines, butters, breakfast cereals and spreads are now enriched with phytosterols and marketed towards people wishing to lower their cholesterol levels.
- Ostlund RE, Racette, SB, and Stenson WF (2003). "Inhibition of cholesterol absorption by phytosterol-replete wheat germ compared with phytosterol-depleted wheat germ". Am J Clin Nutr. 77 (6): 1385–1589.
- De Stefani, Eduardo; et al. (2000). "Plant Sterols and Risk of Stomach Cancer: A Case-Control Study in Uruguay". Nutrition and Cancer. 37 (2): 140–144.
- Li, Thomas S. C. (1633–1639). "Phytosterol content of sea buckthorn (Hippophae rhamnoides L.) seed oil: Extraction and identification". Food Chemistry. Elsevier. 101 (4): 1633–1639. doi:10.1016/j.foodchem.2006.04.033. Retrieved 2006-11-20. Unknown parameter
- Pennington & Douglas, Food Values of Portions Commonly Used, 18th ed. (2005)
- "The Marketing Edge: Phytosterols Qualisoy" (Brochure (PDF)). Qualisoy. Retrieved 2006-11-20.
"Consumption of a Functional Oil Rich in Phytosterols and Medium-Chain Triglyceride Oil Improves Plasma Lipid profiles in Men" (Article (PDF)). Journal Of Nutrition (133): 1815–1820. Unknown parameter
- Detailed Scientific Study of Dietary Phytosterols and the Effect on Cholesterol (Degussa)
- Phytosterol content in food