P-T evolution of paragneisses and amphibolites from Romeleåsen, Scania, southernmost Sweden

Populärvetenskaplig sammanfattning Vad har berget i Romeleåsen varit med om? Jordskorpan är uppbyggd av ett antal plattor. Vid plattgränser under oceanerna bildas ny skorpa av magma som tränger upp. Oceanplattan kan inte öka i storlek. Där oceanplattan möter en platta med kontinental jordskorpa tränger oceanplattan under kontinentalplattan (subduktion, t. ex. Anderna). Vid kollisionen dras sediment från oceanplattan med i djupet och utsätts för höga tryck och temperaturer och omvandlas till ny mineraler, metamorfos. Vid kollisionen bildas också magma som stiger upp och bygger upp en bergskedja. Hettan från magman kan också metmorfosera berggrunden i närheten. Då två kontinentalplattor kolliderar bildas en bergskedja (t. ex. Himalaya) och berget under utsätts för mycket höga tryck och metamorfoseras. Betingelserna (tryck och temperatur) bevaras i mineralernas kemiska sammansättning. Genom att fastställa vilka mineral som finns (paragenes) och deras kemiska sammansättning kan man avgöra vilka betingelser som berget utsatts för och därmed i vilken miljö berget har varit. Romeleåsen är den sydvästligaste blottningen av den Fennoskandiska skölden i Sverige. Berggrunden har påverkats metamorft åtminstone under den hallandiska/dano-poloniska bergsbildningen för 1.47–1.38 miljarder år sedan och under den svekonorvegiska bergsbildingen för 1.10-0.92 miljarder år sedan. För att försöka förstå metamorfosen har petrografin och geokemin studerats för paragnejser och amfiboliter från Romeleåsens mellersta del. Tryck- och temperatur-utvecklingen har bestämts med hjälp av den kemiska sammansättningen för olika mineral (geotermobarometri) och från mineralsammansättningen med användande av jämviktsdiagram. Resultatet visar att berget i mellersta delen av Romeleåsen utsatts för betingelser med maximum vid cirka 750°C och 4-5 kbar. Tryck och temperatur följer ett förlopp medurs med uppvärmning under tryckökning, sedan uppvärmning under trycksänkning och partiell smältning och slutligen avsvalning under fortsatt trycksänkning. Tryck-temperatur utvecklingen tyder på jordskorpeförtjockning och efterföljande upplyftning. Detta har skett i en omgivning med hög temperatur relativt tryck, vilket tyder på samtidig magmatism. Betingelserna tyder på liknande förhållandena som dem i Anderna. För att kunna koppla metamorfosen till hallandisk/danopolonisk eller svekonorvegisk bergkedjebildning krävs geokronologi. Ett lämpligt mineral för detta är zirkon, som finns talrikt i paragnejserna på Romeleåsen.Romeleåsen is the south-westernmost exposure of the Fennoscandian Shield in Sweden. Fennoscandia forms a part of the East European Craton and was extended to the south-west during prolonged episodes of accretion during the period 1.95-1.55 Ga. Metamorphic reworking took at least place during the Hallandian/Danopolonian orogeny at 1.47-1.38 Ga and during the Sveconorwegian orogeny 1.10-0.92 Ga. High-grade metamorphism during the Sveconorwegian orogeny may have overprinted Hallandian/Danopolonian metamorphism fully or only in parts of Romeleåsen. Alternatively is high-grade metamorphism pre-Sveconorwegian and Sveconorwegian metamorphism caused only a retrograde overprint. Petrographic and geochemical studies including geothermobarometry and calculation of pseudosections on paragneisses and amphibolites from the middle part of Romeleåsen were performed with the aim of understanding the metamorphism. The results show that rocks of the middle part of Romeleåsen underwent prograde staurolite-sillimanite grade metamorphism at upper amphibolite to granulite conditions peaking at about 750°C and 4-5 kbar, with formation of Crd + Sill + Grt + Kfs + Ilm + Melt ± Spl ± Bt. A clockwise P-T path is proposed with heating during decompression and partial melting. Later stages involved the formation of sillimanite + biotite at the expense of garnet and cordierite. Local low-temperature and fluid-assisted retrogression caused pseudomorphism of cordierite by muscovite, biotite and chlorite. Also pseudomorphism of ilmenite by rutile-rich fine-grained intergrowths can be observed. The P-T evolution demonstrates burial and exhumation in a high T/P environment, probably due to coeval magmatism. These conditions are in accordance with an accretionary orogenic setting. In order to assign the metamorphism to either the Hallandian/Danopolonian or the Sveconorwegian orogeny, geochronological studies could be performed, as a suggestion on the abundant zircons in the paragneisses

The gut microbiota and cardiovascular health benefits: a focus on wholegrain oats

Existing scientific data suggest that a high intake of wholegrain foods contributes to improved gut health and a reduced risk of cardiovascular disease. Wholegrain oats are rich in dietary fibre and an important source of many bioactive components, including minerals, vitamins and phenolic compounds. The oat β‐glucans have been reported to lower low‐density lipoprotein cholesterol through their ability to increase the viscosity of intestinal chime, change the gut microbiota composition and increase the production of short‐chain fatty acids, which may contribute to the inhibition of hepatic cholesterol synthesis. Oats are also a rich source of phenolic acids, which are predominantly bound to cell wall polysaccharides through ester bonds. This bound state within oats means that phenolic acid bioavailability will largely be determined by interactions with the colonic microbiota in the large intestine. However, results from in vitro, animal and human studies have been inconsistent in relation to the impact of oats on the gut microbiota, possibly due to differences in experimental techniques and because compounds in oats, other than β‐glucans, have not been considered. This review focuses on the interaction of oat β‐glucans and phenolic acids with gut microbiota, and the subsequent link to cardiovascular health

Processing of oat: the impact on oat's cholesterol lowering effect

Epidemiological and interventional studies have clearly demonstrated the beneficial impact of consuming oat and oat-based products on serum cholesterol and other markers of cardiovascular disease. The cholesterol-lowering effect of oat is thought to be associated with the β-glucan it contains. However, not all food products containing β-glucan seem to lead to the same health outcome. Overall, highly processed β-glucan sources (where the oat tissue is highly disrupted) appear to be less effective at reducing serum cholesterol, but the reasons are not well understood. Therefore, the mechanisms involved still need further clarification. The purpose of this paper is to review current evidence of the cholesterol-lowering effect of oat in the context of the structure and complexity of the oat matrix. The possibility of a synergistic action and interaction between the oat constituents promoting hypocholesterolaemia is also discussed. A review of the literature suggested that for a similar dose of β-glucan, (1) liquid oat-based foods seem to give more consistent, but moderate reductions in cholesterol than semi-solid or solid foods where the results are more variable; (2) the quantity of β-glucan and the molecular weight at expected consumption levels (∼3 g day−1) play a role in cholesterol reduction; and (3) unrefined β-glucan rich oat-based foods (where some of the plant tissue remains intact) often appear more efficient at lowering cholesterol than purified β-glucan added as an ingredient

Role of Polysaccharides in Food, Digestion and Health.

Polysaccharides derived from plant foods are major components of the human diet, with limited contributions of related components from fungal and algal sources. In particular, starch and other storage carbohydrates are the major sources of energy in all diets, while cell wall polysaccharides are the major components of dietary fibre. We review the role of these components in the human diet, including their structure and distribution, their modification during food processing and effects on functional properties, their behaviour in the gastro-intestinal tract and their contribution to healthy diets

Nya metoder ger mer information om kostfibers egenskaper och hälsoeffekter

Med nya metoder som fältflödesfraktionering kan effekter av tillverkning och tillagning på lösliga kostfibers egenskaper följas. Genom att mäta genuttryck i blodkroppar efter en måltid kan man också få kunskap om fibrernas påverkan på ämnesomsättningen i kliniska studier

Characterisation of Dietary Fibre Properties to Optimise the Effects on Human Metabolism and the Transcriptome

It is well established that dietary fibre, especially soluble dietary fibre, has beneficial effects and can prevent diseases associated with the modern lifestyle. This has been explained by the viscous effects of soluble fibre, which can reduce or delay the absorption of carbohydrates and fat in the small intestine, resulting in lower blood concentrations of glucose, insulin and cholesterol. Oats, rye, sugar beet fibre and barley, all recognised for their high content of soluble fibre, were investigated in this work. The ability of fibres to form viscous solutions is determined by the concentration, solubility, the polymer molar mass and aggregate formation. The fibre releasability (solubility) and solution behaviour were analysed under physiological conditions to examine the effects of processing, the surrounding matrix and gastrointestinal conditions. Less than half of the β-glucans was released from oat bran when analysed with an in vitro method imitating gastrointestinal digestion, and the same was found regarding the release of pectin from coarse particles of sugar beet fibre. Reducing the particle size by milling improved the releasability, while mixing the milled fractions with a solid food matrix (protein, fat or starch) decreased or delayed it. The effect of food processing on barley β-glucan aggregation was studied using asymmetrical flow field-flow fractionation. Boiling was shown to disrupt the largest aggregates, while higher temperatures also seemed to degrade the polymer chain. Freeze-thaw cycles resulted in cryogelation, which could lead to reduced viscosity. The low pH in the in vitro gastric digestion phase also disrupted the aggregates, but this was followed by re-aggregation/gelation at the neutral pH mimicking the conditions in the small intestine. This may entrap nutrients in the aggregate or gel matrix, thereby reducing absorption. A human study was performed with oats, rye and sugar beet fibre, and mixtures of these three. Fibre-rich meals were optimised to promote high releasability of fibre and retention of aggregates. Changes in traditional biomarkers, as well as in the transcriptome, in response to the fibre-rich meals, were examined in healthy men and women. The postprandial glucose levels were lowered by rye bran, while oat bran lowered the insulin concentrations. The lowering effects may be related to fibre source, the amount of soluble and insoluble fibre and pre-processing of the fibre. In contrast, a spray-dried oat drink increased the postprandial levels of insulin, possibly due to its low fibre content in combination with certain amino acids and a high amount of carbohydrates in the liquid matrix. Women showed, on average, a more pronounced glucose lowering response than men, indicating that different amounts of dietary fibre should be recommended for men and women. Changes in gene expression in peripheral blood mononuclear cells after the intake of oat bran were investigated with microarray analysis. Gene sets and pathways related to insulin secretion were significantly suppressed in response to the oat bran meal compared with the control meal. In conclusion, many factors may influence the properties of dietary fibre. It is therefore valuable to use in vitro methods to simulate gastrointestinal digestion to characterise and optimise fibre functionality prior to testing their effects on human metabolism and the transcriptome