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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Levan is a naturally occurring fructan present in many plants and microorganisms. [1] This polymer is made up of fructose, a monosaccharide sugar, connected by 2,6 beta glycosidic linkages. Levan can have both branched and linear structures of relatively low molecular weight. [2] Branched levan forms a very small, sphere-like structure [3] with basal chains 9 units long. The 2,1 branching allows methyl ethers to form and create a spherical shape. The ends of levan also tend to contain a glucosyl residue. [4] Branched levan tends to be more stable than the linear structure. [5] However, the amount of branching and length of polymerization tends to vary among different species. [4] The shortest levan is 6-kestose, a chain of two fructose molecules and a terminal glucose molecule.
Levan was first discovered through research on nattō, a traditional Japanese dish. [5] Natto was known as a "superfood" which promoted health and longevity in Japan during the late 1800s. [5] In 1881, Lippmann first discovered "lävulan" (levan) as the remaining gum from molasses in sugar beet production. [6] Later in 1901, Greig-Smith coined the name “levan” based on the levorotatory properties of this substance in polarized light.
Levan is synthesized in archaea, fungi, bacteria, and a limited number of plant species. Fructans such as levan are synthesized from sucrose, a disaccharide containing glucose and fructose. [5] In plants, the vacuole is where fructan production occurs. Sucrose:sucrose/fructan 6-fructosyltransferase is the fructosyltransferase in the vacuole which creates the beta 2,6 linkages to form the linear form of levan. [5] Bacteria also use a fructosyltransferase known as levansucrase to form levan. [5] These enzymes in bacteria form the 2,1 linkages in the linear basal chains of levan to allow for branching points to occur. [5] Many bacteria produce levan in the cell exterior. [5] This production can be sensitive to temperature, oxygen concentration, pH, and other factors. [5] Levan production in bacteria is typically a sign of growth in population. [5] There are also possible ways to produce by fracturing soybean mucilage.[ citation needed ]
Levans are produced by microbes during colonization of a food substrate. Erwinia amylovora exudes levan and amylovoran as part of its biofilm. Together they contribute to its pathogenicity. [7] In 2016, Ua-Arak et al. developed a sourdough method with high levan output (among other exopolysaccharides). [8]
The beta 2,6 linkages of levan allow for it to be soluble in both water and oil; however, the water temperature varies the degree of solubility. [9] Levan also is insoluble in many organic solvents such as methanol, ethanol, and isopropanol. [4] The branching of levan allows it to have a high tensile and cohesive strength, while the hydroxyl groups contribute to adhesion with other molecules. [4] The intrinsic viscosity n, a measure of the substance effect on viscosity of a solution, tends to be very low for levan. [4] This allows levan to be utilized in a pharmaceutical setting.
Many industries such as food, beverages, cosmetics, and even medicine utilize levan in their products. One of the reasons levan is able to be used in such a versatile way is that it fulfills all safety guidelines. Levan does not cause any form of skin or eye irritation, has not shown any allergenic effects, and poses no threat of cytotoxicity. [10]
In the food industry, levan is incorporated due to its prebiotic effects, cholesterol lowering ability, and adhesive properties. [4] It also occurs naturally in low amounts in food for human consumption. [4] Levan is also included in many dairy products as fiber or sweetener. [4] Commercial, non-alcoholic beverages use levan as well in ultra-high-fructose-syrups. [11] Interestingly, levan causes useful bacterial growth and proliferation which can be especially important in the gut because it causes a decrease in population of the pathogenic bacteria. [12]
Levan can be used for hair care and skin whitening. In hair care products, levan acts to form a film which creates a hair holding effect utilized in various gels and mousses. [5] Levan is used as a skin whitener as well because it has been tested to show inhibition on melanin production by decreasing the activity of the enzyme tyrosinase which is responsible for melanogenesis. [5]
Levan has shown uses for burned tissue, anti-inflammation, and aquaculture. By combining levan into a thin film, it is able to activate an enzyme known as metalloproteinase which increases the recovery and healing process. [13] In the case of inflammation, levan interacts with the aggregating cells and affects their adhesion to the blood vessel causing reduced accumulation. [14] In aquaculture, results have shown that levan incorporated diets could possibly cause an increase in aggregation of viruses allowing for easier phagocytic removal. [15] Levan produced by Pantoea agglomerans ZMR7 was reported to decrease the viability of rhabdomyosarcoma (RD) and breast cancer (MDA) cells compared with untreated cancer cells. In addition, it has high antiparasitic activity against the promastigote of Leishmania tropica [16]
Polysaccharides, or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with water (hydrolysis) using amylase enzymes as catalyst, which produces constituent sugars. They range in structure from linear to highly branched. Examples include storage polysaccharides such as starch, glycogen and galactogen and structural polysaccharides such as cellulose and chitin.
Inulins are a group of naturally occurring polysaccharides produced by many types of plants, industrially most often extracted from chicory. The inulins belong to a class of dietary fibers known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes. Most plants that synthesize and store inulin do not store other forms of carbohydrate such as starch. In the United States in 2018, the Food and Drug Administration approved inulin as a dietary fiber ingredient used to improve the nutritional value of manufactured food products. Using inulin to measure kidney function is the "gold standard" for comparison with other means of estimating glomerular filtration rate.
An oligosaccharide is a saccharide polymer containing a small number of monosaccharides. Oligosaccharides can have many functions including cell recognition and cell adhesion.
Fructooligosaccharides (FOS) also sometimes called oligofructose or oligofructan, are oligosaccharide fructans, used as an alternative sweetener. FOS exhibits sweetness levels between 30 and 50 percent of sugar in commercially prepared syrups. It occurs naturally, and its commercial use emerged in the 1980s in response to demand for healthier and calorie-reduced foods.
Prebiotics are compounds in food that foster growth or activity of beneficial microorganisms such as bacteria and fungi. The most common environment considered is the gastrointestinal tract, where prebiotics can alter the composition of organisms in the gut microbiome.
Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped (bacilli) or spherical (cocci) bacteria that share common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and milk products, produce lactic acid as the major metabolic end product of carbohydrate fermentation, giving them the common name lactic acid bacteria (LAB).
A fructan is a polymer of fructose molecules. Fructans with a short chain length are known as fructooligosaccharides. Fructans can be found in over 12% of the angiosperms including both monocots and dicots such as agave, artichokes, asparagus, leeks, garlic, onions, yacón, jícama, barley and wheat.
Agave syrup, also known as maguey syrup or agave nectar, is a sweetener commercially produced from several species of agave, including Agave tequilana and Agave salmiana. Blue-agave syrup contains 56% fructose as a sugar providing sweetening properties.
Pantoea is a genus of Gram-negative bacteria of the family Erwiniaceae, recently separated from the genus Enterobacter. This genus includes at least 20 species. Pantoea bacteria are yellow pigmented, ferment lactose, are motile, and form mucoid colonies. Some species show quorum sensing ability that could drive different gene expression, hence controlling certain physiological activities. Levan polysaccharide produced by Pantoea agglomerans ZMR7 was reported to decrease the viability of rhabdomyosarcoma (RD) and breast cancer (MDA) cells compared with untreated cancer cells. In addition, it has high antiparasitic activity against the promastigote of Leishmania tropica.
Curdlan is a water-insoluble linear beta-1,3-glucan, a high-molecular-weight polymer of glucose. Curdlan consists of β-(1,3)-linked glucose residues and forms elastic gels upon heating in aqueous suspension. It was reported to be produced by Alcaligenes faecalis var. myxogenes. Subsequently, the taxonomy of this non-pathogenic curdlan-producing bacterium has been reclassified as Agrobacterium species.
Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental component that determines the physicochemical properties of a biofilm. EPS in the matrix of biofilms provides compositional support and protection of microbial communities from the harsh environments. Components of EPS can be of different classes of polysaccharides, lipids, nucleic acids, proteins, lipopolysaccharides, and minerals.
The enzyme levan fructotransferase (DFA-IV-forming) catalyzes the following process:
Levansucrase is an enzyme that catalyzes the chemical reaction
Microbiology is the scientific study of microorganisms, those being of unicellular (single-celled), multicellular, or acellular. Microbiology encompasses numerous sub-disciplines including virology, bacteriology, protistology, mycology, immunology, and parasitology.
David Sidney Feingold was an American biochemist.
Glucansucrase is an enzyme in the glycoside hydrolase family GH70 used by lactic acid bacteria to split sucrose and use resulting glucose molecules to build long, sticky biofilm chains. These extracellular homopolysaccharides are called α-glucan polymers.
Chitin-glucan complex (CGC) is a copolymer (polysaccharide) that makes up fungal cell walls, consisting of covalently-bonded chitin and branched 1,3/1,6-ß-D-glucan. CGCs are alkaline-insoluble. Different species of fungi have different structural compositions of chitin and β-glucan making up the CGCs in their cell walls. Soil composition and other environmental factors can also affect the ratio of chitin to β-glucan found in the CGC. Fungal cell walls may also contain chitosan-glucan complexes, which are similar copolymers but have chitosan instead of chitin. Chitin and chitosan are closely related molecules: greater than 40% of the polymer chain of chitin is made of acetylated glucosamine units, whereas greater than 60% of chitosan is made of deacetylated glucosamine units.
Botryosphaeran is an exopolysaccharide (EPS) produced by the ascomyceteous fungus Botryosphaeria rhodina. Characterization of the chemical structure of botryosphaeran showed this EPS to be a (1→3)(1→6)-β-D-glucan. This particular β-glucan can be produced by several strains of Botryosphaeria rhodina that include: MAMB-05, DABAC-P82, and RCYU 30101. Botryosphaeran exhibits interesting rheological properties and novel biological functions including hypoglycaemia, hypocholesterolaemia, anti-atheroslerosis and anti-cancer activity, with potential commercial applications. Three cosmetic products formulated with botryosphaeran have been developed to promote skin health and treat skin conditions for future intended commercialization purposes.
Kestose is a class of sugars that belongs to a group of fructooligosaccharides.
Mutan is a sticky colorless water-insoluble glucan with predominant α-1-3 linkages is the major component of dental biofilms, which enhances the formation of dental plaque and dental caries. It is a source made from glucans which are derived form glucose monomers. Little to nothing is known about the alpha glucans that make up the water-insoluble linkages of mutan with dexteran. These values can be derived using NMR techniques.