Plant sterols are an essential component of the membranes of all eukaryotic organisms. They are either synthesised de novo or taken up from the environment. Their function appears to be to control membrane¯uidity and permeability, although some plant sterols have a speci®c function in signal transduction. The phytosterols are products of the isoprenoid pathway. The dedicated pathway to sterol synthesis in photosynthetic plants occurs at the squalene stage through the activity of squalene synthetase. Although the activity of 3-hydroxymethyl-3-glutaryl coenzyme A (HGMR) is rate-limiting in the synthesis of cholesterol, this does not appear to be the case with the plant sterols. Up-regulation of HGMR appears to increase the biosynthesis of cycloartenol but not the D 5-sterols. A decline in sterol synthesis is associated with a suppression of squalene synthetase activity, which is probably a critical point in controlling carbon¯ow and end-product formation. The major post-squalene biosynthetic pathway is regulated by critical rate-limiting steps such as the methylation of cycloartenol into cycloeucalenol. Little is known about the factors controlling the biosynthesis of the end-point sterol esters or stanols. The commonly consumed plant sterols are sitosterol, stigmasterol and campesterol which are predominantly supplied by vegetable oils. The oils are a rich source of the steryl esters. Less important sources of sterols are cereals, nuts and vegetables. The nutritional interest derives from the fact that the sterols have a similar structure to cholesterol, and have the capacity to lower plasma cholesterol and LDL cholesterol. Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using cholesterol-lowering drugs (statins), the interest in plant sterols lies in their potential to act as a natural preventive dietary product. Stanols (saturated at C-5) occur in low amounts in the diet and are equally effective in lowering plasma cholesterol and do not cause an increase in plasma levels, unlike the sterols which can be detected in plasma.

Plant sterols are an essential component of the membranes of all eukaryotic organisms. They are either synthesised de novo or taken up from the environment. Their function appears to be to control membrane fluidity and permeability, although some plant sterols have a specific function in signal transduction. The phytosterols are products of the isoprenoid pathway. The dedicated pathway to sterol synthesis in photosynthetic plants occurs at the squalene stage through the activity of squalene synthetase. Although the activity of 3‐hydroxymethyl‐3‐glutaryl coenzyme A (HGMR) is rate‐limiting in the synthesis of cholesterol, this does not appear to be the case with the plant sterols. Up‐regulation of HGMR appears to increase the biosynthesis of cycloartenol but not the Δ5‐sterols. A decline in sterol synthesis is associated with a suppression of squalene synthetase activity, which is probably a critical point in controlling carbon flow and end‐product formation. The major post‐squalene biosynthetic pathway is regulated by critical rate‐limiting steps such as the methylation of cycloartenol into cycloeucalenol. Little is known about the factors controlling the biosynthesis of the end‐point sterol esters or stanols. The commonly consumed plant sterols are sitosterol, stigmasterol and campesterol which are predominantly supplied by vegetable oils. The oils are a rich source of the steryl esters. Less important sources of sterols are cereals, nuts and vegetables. The nutritional interest derives from the fact that the sterols have a similar structure to cholesterol, and have the capacity to lower plasma cholesterol and LDL cholesterol. Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using cholesterol‐lowering drugs (statins), the interest in plant sterols lies in their potential to act as a natural preventive dietary product. Stanols (saturated at C‐5) occur in low amounts in the diet and are equally effective in lowering plasma cholesterol and do not cause an increase in plasma levels, unlike the sterols which can be detected in plasma. © 2000 Society of Chemical Industry

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Cereal Chem. 79(1):148-154The total plant sterol contents (free sterols and covalently bound structures) of the main cereals cultivated in Finland were determined. Furthermore, sterol contents were determined for different flour and bran fractions in the milling process of wheat and rye, as well as plant sterol contents in various milling and retail bakery products. The sample preparation procedure included acid and alkaline hydrolysis to liberate sterols from their glycosides and esters, respectively. Free sterols were extracted and, after recovery using solid-phase extraction, derivatized to trimethylsilyl ethers for gas chromatography (GC) analysis. We used GC with a mass spectrometer (MS) for identification. When two cultivars of rye, wheat, barley, and oats grown in the same year were compared, the highest plant sterol content was observed in rye (mean content 95.5 mg/100 g, wb), whereas the total sterol contents (mg/100 g, wb) of wheat, barley, and oats were 69.0, 76.1, and 44.7, respectively. In addition, the 10 rye cultivars and breeding lines compared had total sterol contents of 70.7-85.6 mg/100 g. In the milling process of rye and wheat, the plant sterols fractionated according to the ash content of the corresponding milling product. In all cereal grain and milling product samples, sitosterol was the main sterol. The level of stanols differed in the different milling process samples; it was lower in the most refined rye and wheat flours (≈15%) than in the bran fractions (≈30% in the bran with 4% ash content). Rye bread with whole meal rye flour as the main or only ingredient was a good source of sterols. Sterol content was higher than that of wheat bread, whereas plant sterol content of other bakery products was affected by the type and amount of fat used in baking.

The plant sterol contents of the most important vegetables, fruits and berries available in Finland were determined by capillary gas chromatography. The sample preparation procedure included both acid and alkaline hydrolysis to liberate sterols from their conjugates. The plant sterol contents of fresh vegetables ranged from 51 to 370 mg kg À1 fresh weight (fw) in samples obtained from retail sale. The highest contents (>300 mg kg À1 ) were measured in broccoli, Brussels sprouts, cauliflower and dill and the lowest (51 mg kg À1 ) in potato. The range of sterol contents on a dry weight (dw) basis was high, 246-4100 mg kg À1 dw. Considerable variation was also observed when individual samples of some vegetables were compared. Sitosterol was the main sterol (proportion 43-86%) in all vegetables except cucumber and spinach, in which D 7 -sterols dominated. The total sterol contents were in the range 116-228 mg kg À1 fw in all fresh fruits except avocado, which contained more sterols, 752 mg kg À1 fw. In fresh berries the corresponding range was 60-279 m kg À1 fw. The wild berries lingonberry and blueberry were better plant sterol sources than the cultivated berries blackcurrant, redcurrant and strawberry. In fruits and berries the proportion of sitosterol ranged from 61-93% total sterols. On the basis of the results, the contribution of vegetables, fruits and berries to the total average daily plant sterol intake was estimated to be ca 60 mg.