Phytosterol

    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.

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Specific phytosterols

• 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).

Uses

Plant structure

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.

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. [1]

Lowering cholesterol

As a food ingredient or additive, phytosterols have cholesterol-lowering properties (reducing cholesterol absorption in intestines),^[1] and may act in cancer prevention.^[2] Phytosterols occur naturally in small quantities in vegetable oils, especially sea buckthorn oil (1640mg/100g oil),^[3] corn oil (968mg/100g),^[4] and soybean oil (327mg/100g oil).^[5] 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%.^[6]

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.

References