Beta glucans

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Beta-glucans (β-glucans) are a group of high-molecular β-D-glucose polysaccharides which are found in the cell walls of cereals, bacteria and fungi. Depending on the source, they have significantly different physicochemical properties. Also, cellulose and chitin are glucans with β- glycosidic linkage . Some β-glucans have anti-tumor and anti-inflammatory effects.

properties

A daily intake of 3 g beta-glucan from barley reduces the LDL level and can lower the risk of cardiovascular disease . Some studies suggest that beta-glucans from grains also have immunomodulatory properties. Beta-glucans are used as soluble fiber in various medically used food supplements and in cosmetic products, as well as texturizing agents in foods. When brewing beer , beta-glucans are produced as undesirable by-products, as they are an indicator of reduced malting and increase the viscosity of the wort .

Beta-glucans with β- (1 → 3) and β- (1 → 6) branches bind to the receptors dectin-1 , complement receptor 3 (CR3) and toll-like receptors (TLR).

Beta-glucans were first discovered in lichens and shortly afterwards in barley.

Occurrence

β-glucans are a natural component of the cell walls of bacteria, fungi, yeast and cereals such as oats and barley. The different types of beta-glucans are characterized by different molecular structures, also by different degrees of branching and different molecular weights, which cause their solubility and physiological properties. Beta-glycosidic bonds cannot be metabolized by humans because they do not have enzymes to break the β-glycosidic bond. That is why beta-glucans belong to the fiber category.

Beta-glucans from cereals consist of β-1,3 and β-1,4 linked D-glucopyranose units. Yeast beta-glucans are β-1,3- and β-1,6-glyosidically linked. The beta-glucans in barley are 27% in the walls of the aleuron cells and 73% in the cell walls of the endosperm , while the beta-glucans in oats are concentrated in the subaleuron layer. The bread grains wheat (0.8%) and rye (2.3%) contain only small amounts of beta-glucan. One of the most common sources of beta-1,3-D- glucans for dietary supplements is obtained from the cell wall of the baker's yeast Saccharomyces cerevisiae . The β (1,3) D-glucans obtained from baker's yeast are often insoluble. Beta-1,3- and beta-1,4-glucans are also extracted from oat bran and from the core of barley. The grains of beta-glucan barley also serve as a beta-glucan supplier in the form of barley flakes and barley flour for bread and baked goods. Other sources include some types of algae and different types of mushrooms such as Reishi ( Shiny Lackporling , Ganoderma lucidum ), Ganoderma applanatum , Shiitake , Chaga ( Slate Schillerporling ), and Maitake ( Common Rattles ).

effect

Beta-glucans from oats and barley produce a variety of physiological effects, some of which have a positive effect on health. Barley and oat β- glucans were studied in subjects with hypercholesterolemia for their effects on reducing the risk of heart attack. Beta-1,3 / 1,4-glucan presumably lowers a high cholesterol level and thus reduces an important risk factor for vascular diseases such as arteriosclerosis, high blood pressure, heart attack and stroke.

Beta-glucans from grains increase the viscosity of the chyme in the gastrointestinal tract if the concentration in food is sufficiently high . They delay the breakdown of nutrients, especially the breakdown of carbohydrates into sugar and their absorption into the blood. The consumption of oat and barley products with a high beta-glucan content leads to a lower increase in blood sugar level after meals and a reduced secretion of insulin. The risk of obesity and other diet-related diseases such as type 2 diabetes, heart attack and stroke decreases.

As soluble fiber, the beta-glucans are fermented by the intestinal flora to form anions of short-chain fatty acids such as acetate, butyrate and propionate. The resulting lowering of the pH value prevents in particular the colonization of the colon by pathogenic germs. Short-chain fatty acids are important regulators for a healthy metabolism. Butyrate is the most important source of energy for the intestinal mucous membrane cells and has an anti-inflammatory effect.

β-D-glucan is part of the cell wall of certain medically relevant fungi, in particular the fungus species watering can mold ( Aspergillus ) and mushrooms (also Agaricus ). The determination of the presence of β-D-glucan in the blood is therefore also marketed as a method for diagnosing invasive fungal infections in patients. False positives can result from fungus - contamination in antibiotics such as clavulanic acid - amoxicillin , and piperacillin / tazobactam occur. False positive results can also occur due to contamination of clinical samples with the bacteria Streptococcus pneumoniae , Pseudomonas aeruginosa and Alcaligenes faecalis , which also produce (1 → 3) β-D-glucan. Fungal beta-glucans have been recognized as "modifiers of the biological immune response". Beta-1,3-1,6- glucans as essential components of the cell walls of fungi, some plants and bacteria are structures that are recognized by our immune system as quasi-pathogens. Without being a pathogen, they trigger immune activation, but do not cause symptoms of illness. Beta-glucans are recognized and absorbed by phagocytes via special receptors (Dectin-1 and others). As a result, the phagocytes activate the formation of additional cells for the immune defense, which can then protect the body from new pathogens in the blood and lymphatic systems. This regulation of the immune response also causes anti-tumor properties. Several studies have found effects on epithelial cell cytokine production.

Individual evidence

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See also