Fructans, molecular weight

From sedimentation and diffusion measurements, Ogston has determined the molecular weight of the fructans from both leafy cocksfoot grass (Dacty-lis glomerata) and Italian rye grass (Lolium italicum) to be 5,500.261 Both polysaccharides were polymolecular, and the data indicated a singly-branched structure for each. 

The composition of the products was monitored by HPLC (Sugar Analyzer, Waters Associates HPX-87C column, BioRad Corp. with deionized water, 40 ppm in calcium acetate as mobile phase). During fermentation, the sucrose levels dropped and fructan started to appear in 2 days thereafter, sucrose level gradually decreased as fructan increased. Glucose was the major by-product. A small amount of fructose and other unidentified fermentation products smaller in molecular weight were also observed. The pH of the growth medium was controlled, and fell from... 

Fructan fructan fructosyl transferase has a molecular weight of approximately 70 kDa and can be separated into five species with pH values between 4.5 and 5.0. The enzyme has a pH optimum for fructosyl transfer activity between 5.5 and 7.0 and a temperature optimum in the 25 to 35°C range. Like 1-SST, 1-FFT has a low Q10 (i.e., 1.14 between 25 and 5°C), indicative of its ability to function at relatively low temperatures (Koops and Jonker, 1994). The rate of transfer of fructosyl groups increases with substrate concentration up to 100 mol nr3. 

Particular difficulties exist, however, in purifying dextrans synthesized by many streptococci, because the bacteria simultaneously elaborate exocellular fructans (levansDextrans and levans synthesized concomitantly by Leuconostoc micro-organisms have been separated by fractionally precipitating the polysaccharides from aqueous ethanol. These separative procedures are, however, only effective when considerable differences in molecular weight exist between the main fractions of the two polysaccharides, and, as a result, they are of limited value in effecting separation of levans from many streptococcal dextrans. Reports that some oral bacteria are able to metabolize levans suggest that... 

The plant fructans are of two main types, the linear P2,6-fructans (levans) and the linear P2,l-fructans (inulins). A third class contains both types of linkage and is highly branched. Bacterial levans, by contrast, are mostly composed of a predominance of P2,6 sequences with P2,l branches at rather less frequent intervals than in the branched fructans of plants. Whereas bacterial levans have molecular weights often in excess of one million daltons, the plant fructans seldom reach one-hundreth of this size. 

The fructans produced are of hetergeneous molecular weight, but the chains are not extended much beyond 35 residues, for reasons that are not known. 

This fructosyltransferase and the related fructan is interesting for many possible applications. Only based on sucrose as raw material high molecular weight inulin, preferably without branches similar to plant inulin, can be produced in aqueous solution. Scale-up is the same as the production design for dextran or neo-amylose. The utilization of the simultaneously formed glucose as food, feed or fermentation medium should be no problem. 

A mixed-type P-D-fructan comprising (2 1)-linked and (2- 6)-linked unbranched P-o-Fru/ residues and a-D-Glcp residues. Isol. from red squill (Urginea maritima). Used as a diagnostic test of renal function (alternative to inulin). Sol. H2O. [o(]d -45.5 (c, 1 in H2O). Molecular weight distribution 800-16000. 

Fructans are polymers of fructose stored in some plants as reserve material instead of starch. They have much lower molecular weight than starch, and are water soluble. The branched fructans are found mainly in the grass (Poaceae) and lily (Liliaceae) families while linear fructans (specifically inulin) are particularly common in the Aster-aceae. Fructans are composed almost entirely of fructosyl-fructose linkages, and in some cases glucose molecules are present in the chain (Cseke and Kaufman 1999). 

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