Vieno Piironen

Plant sterols : biosynthesis, biological function and their importance to human nutrition

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. n n© 2000 Society of Chemical Industry

Plant Sterols in Cereals and Cereal Products

ABSTRACT The 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 ry...

The HEALTHGRAIN Wheat Diversity Screen: Effects of Genotype and Environment on Phytochemicals and Dietary Fiber Components

Analysis of the contents of bioactive components (tocols, sterols, alkylresorcinols, folates, phenolic acids, and fiber components) in 26 wheat cultivars grown in six site x year combinations showed that the extent of variation due to variety and environment differed significantly between components. The total contents of tocols, sterols, and arabinoxylan fiber were highly heritable and hence an appropriate target for plant breeding. However, significant correlations between the contents of bioactive components and environmental factors (precipitation and temperature) during grain development also occurred, with even highly heritable components differing in amount between grain samples grown in different years on different sites.

Phytosterols in Wheat Genotypes in the HEALTHGRAIN Diversity Screen

The phytosterol contents of 130 winter wheat, 20 spring wheat, 10 durum wheat, 5 spelt, 5 einkorn, and 5 emmer wheat genotypes, grown at the same location in the same year, were analyzed with gas chromatography. Considerable variation was observed in total phytosterol contents in all wheat types. The total sterol contents ranged from 670 to 959 microg/g of dm in winter wheat and from 797 to 949 microg/g of dm in spring wheat. The highest sterol contents were found in spelt, durum wheat, and einkorn wheat. The proportions of the main phytosterols also varied substantially among the different genotypes. The most abundant phytosterol in all wheat genotypes was sitosterol (40-61% of total sterols), whereas the highest variation was seen in total stanols (7-31% of total sterols). The comprehensive data set produced in this study constitutes a valuable basis for plant breeding and selection of phytosterol-rich genotypes.

Fermented Wheat Bran as a Functional Ingredient in Baking

ABSTRACT The aim of the current study was to identify factors influencing the technological functionality of fermented bran. The influences of fermentation type and type of wheat bran on the microbial community, bioactivity, arabinoxylans (AX), and activity of xylanases were studied in the bran ferments. Furthermore, technological quality of ferments was established by using them to replace wheat in baking with a 20% substitution level. Solubilization of AX and endogenous xylanase activity of bran were influenced by the type of bran, fermentation type, and conditions. Peeled bran had a clearly reduced microbial load and different microbial community in comparison to native bran. Bran from peeled kernels contained 10-fold lower activities of endogenous xylanases in comparison to native bran. Yeast fermentation of bran from peeled kernels increased the level of folates (+40%), free phenolic acids (+500%), and soluble AX (+60%). Bread containing yeast-fermented peeled bran had improved volume (+10–15%) and c...

Natural variation in grain composition of wheat and related cereals

The wheat grain comprises three groups of major components, starch, protein, and cell wall polysaccharides (dietary fiber), and a range of minor components that may confer benefits to human health. Detailed analyses of dietary fiber and other bioactive components were carried out under the EU FP6 HEALTHGRAIN program on 150 bread wheat lines grown on a single site, 50 lines of other wheat species and other cereals grown on the same site, and 23-26 bread wheat lines grown in six environments. Principal component analysis allowed the 150 bread wheat lines to be classified on the basis of differences in their contents of bioactive components and wheat species (bread, durum, spelt, emmer, and einkorn wheats) to be clearly separated from related cereals (barley, rye, and oats). Such multivariate analyses could be used to define substantial equivalence when novel (including transgenic) cereals are considered.

Effect of soybean processing on content and bioaccessibility of folate, vitamin B12 and isoflavones in tofu and tempe.

PURPOSEnTo compare the content of bioaccessible folate, vitamin B12, and isoflavones in tofu and tempe, as influenced by soybean variety and food processing, particularly fermentation.nnnPRINCIPAL RESULTSnRaw soybeans contained 2207-2671 μg/kg (dry matter) folate, cooked tempe 1493-4143, and cooked tofu 968-1273 μg/kg, the difference was attributed to the fermentation in tempe. Vitamin B12 was detected only in tempe (0.16-0.72 μg/kg). Isoflavone aglycones were formed during soaking of soybeans, with only minor differences between the contents in cooked tempe (average 1922-2968 μg/kg) or tofu (1667-2782 μg/kg) but strongly depending on bean variety.nnnCONCLUSIONSnFolate and vitamin B12 contents were mainly influenced by microbial activity during fermentation, whereas isoflavone aglycone content was determined by bean variety. Tofu had lower folate and vitamin B12, but equal isoflavone contents as tempe. Bioaccessibility of folate (80-100%) and isoflavone aglycones (100%) were high.

Effect of SPME extraction conditions and humidity on the release of volatile lipid oxidation products from spray-dried emulsions.

The aim of the study was to investigate the effects of headspace solid-phase microextraction (HS-SPME) conditions and relative humidity (RH) on the release of volatile lipid oxidation products from spray-dried emulsions. Two model spray-dried sunflower oil emulsions with a Na-caseinate-maltodextrin matrix were oxidised, stabilised at five RHs and analysed by HS-SPME-GC-MS for volatiles. Increased extraction temperature raised not only the overall release of volatile compounds but also altered the volatile profile. The obtained volatile profiles were dependent on the RH. This was mainly due to the humidity response of the matrix affecting e.g. its binding ability and hydrophilicity. Cross-linking of the emulsifying protein had a minor influence on the release. Both matrix-related factors and extraction conditions should thus be taken into account in interpretation of the HS-SPME results. On the other hand, being sensitive to changes in matrix composition and structure, the HS-SPME allows studying of matrix-related changes in foods.

In situ enrichment of folate by microorganisms in beta-glucan rich oat and barley matrices.

The objective was to study folate production of yeast strains, bacteria isolated from oat bran, and selected lactic acid bacteria as well as one propionibacterium in oat and barley based models. Simultaneously, we aimed at sustaining the stability of viscosity, representing the physicochemical state of beta-glucan. Total folate contents were determined microbiologically and vitamers for selected samples by UHPLC. Folate in yeast cells comprised mainly 5-methyltetrahydrofolate and tetrahydrofolate. Folate production by microbes in YPD medium was different to that in cereal fermentations where vitamers included 5-methyltetrahydrofolate, 5,10-methenyltetrahydrofolate and formylated derivatives. Microbes producing significant amounts of folate without affecting viscosity were Saccharomyces cerevisiae ALKO743 and Candida milleri ABM4949 among yeasts and Pseudomonas sp. ON8 and Janthinobacterium sp. RB4 among bacteria. Net folate production was up to 120 ng/g after 24 h fermentation and could increase during 2-week storage. Glucose addition increased the proportion of 5-methyltetrahydrofolate. Streptococcus thermophilus ABM5097, Lactobacillus reuteri, and Propionibacterium sp. ABM5378 produced folate but in lower concentrations. Both endogenous and added microbes contribute to folate enhancement. Selection of microbes with folate producing capability and limited hydrolytic activity will enable the development of products rich in folate and beta-glucan.

Effects of Environment and Genotype on Phytosterols in Wheat in the HEALTHGRAIN Diversity Screen

The effects of environment on the content and composition of phytosterols were examined in 26 wheat genotypes grown at four locations in Europe during a single year and at one location over three consecutive years. Total phytosterol contents varied among the locations, whereas no effect was found for the harvesting year. A significant genetic variation was observed in total sterol contents (700-928 microg/g of dm). The genotype and environment resulted in statistically significant differences in the proportions of the main phytosterols. The high phytosterol contents were characterized by low proportions of sitosterol and high proportions of stanols. Small wheat kernels with proportionally high bran yield and lipid content contained higher levels of phytosterols than large kernels. Knowledge of the level and variability of phytosterols in wheat enables the selection of genotypes with high and stabile phytosterol contents for cultivation or plant breeding purposes.