Bacterial inulin

Inulin is characterized by a p-(2—>1) linked backbone and is generally found as reserve carbohydrate in plants such as chicory (up to 20%), Jerusalem artichoke, and onion, and also in some bacteria. Plant inulin has a degree of polymerization (DP) with a maximum up to 200, which depends on the plant species and their life-cycle. Bacterial inulin has a much higher DP (from 10,000 to more than 1(X),000) but is also highly branched (>15%). Both DP and the presence of branches are important properties since they influence the functionality of the inulin. Many possible applications demand a high molecular weight inulin like bacterial inulin, but without branches. 

This obvious structural difference between plant and bacterial inulin has its origin in the individual synthesis related system. Feedstock for both inulins is sucrose. However, the plant inulin production is a two-step reaction, starting with a sucrose-1-fructosyltransferase (1-SST). One sucrose molecule acts as donor and a second one as acceptor of a fructosyl unit. This leads to the formation of the trisaccharide 1-kestose. Catalyzed by a fructan-fructan-1-fructosyltransferase (1-FFT), fructosyl units are shuffled between the 1-kestose and higher polymeric p-(2 1) linked fructan molecules in the second step. Repetition of this step results in inulin with (3-(2 1) linkages only [129-132]. 

Only the fructosyltransferase (FTF, EC 2. 4. 1. 9) is required in bacteria for the synthesis of bacterial inulin. The enzyme shuffles fructosyl units from one sucrose molecule (acting as druior) to another sucrose molecule, 1-kestose, and higher polymeric p-(2 1) linked fructan molecules, respectively (acting as acceptor). This enzyme partly leads to p-(2—>6) linkages, which results in branches within the inulin molecule [130, 133]. 

For the production of bacterial inulin only the enzyme fructosyl transferase (FTF, EC 2.4.1.9) is required, which shuffles fructosyl units from the sucrose donor to another sucrose molecule or 1-kestose or higher polymeric p-(2- 1) linked fructan molecules acting as acceptor. The enzyme partly leads... 

Two extracellular D-fructans, (2- 6)-linked S-D-fructofuranan or levan and the less common corresponding (2 l)-linked polysaccharide, of the inulin type, are elaborated by different bacteria. These polysaccharides are formed from sucrose by the action of sucrose fructosyltransferases. Terminal )S-D-fructofuranosyl groups are present in some bacterial heteropolysacchar-... 

ROLAND I R, RUMNEY 0 J, couTTS J T, LiEVENSE L c (1998) Effect of Bifidobactcrium longum and inulin on gut bacterial metabolism and carcinogen-induced crypt foci in rats. ... 

Structure. The nmr spectra, shown in Figure 2, indicates that essentially all fructose molecules in the polymers are in the same conformation. In Table I, nmr peaks from fructan are compared to peaks from known inulin 0-(l->2) linked) and bacterial levan (P-(2->6) linked). Data clearly show the fructan to be of the p-(2- 6) type (27). (Sec Table II.)... 

Many pioneer structural investigations were carried out in other groups of polysaccharides, notably on inulin, on the xylan from esparto, on the mannan from yeast and on a series of bacterial polysaccharides amongst the latter were included somatic and lipoid-bound polysaccharides from M. tuberculosis. Noteworthy also was the work on the dextran produced by strains of Leuconostoc, which is showing grqat promise as a blood plasma substitute. 

Polysaccharides that exclusively contain D-fructose are known as fructans and there are two known kinds, inulin and levan. Inulin is a polysaccharide containing -D-fructofuranose linked (2 1) [118]. Inulins are found in the roots and tubers of the family of plants known as the Compositae, which includes asters, dandelions, dahlias, cosmos, burdock, goldenrod, chicory, lettuce, and Jerusalem artichokes. Other sources are from the Liliacae family, which includes lily bulbs, onion, hyacinth, and tulip bulbs. Inulins are also produced by certain species of algae [119]. Several bacterial strains of Streptococcus mutans also produce an extracellular inulin from sucrose [120]. 

D-Fructofuranosides occur abundantly in Nature. They occur in plants, examples include inulin, levan, and sucrose, and also in bacterial cell-walls and capsules such as those of species of Streptococcus, Haemophilus, and Yersinia 85 Unfortunately, synthesis of their glycosides presents the same type of problem as that in the synthesis of (3-mannosides, namely difficulty of approach of a nucleophile from the [3 side ... 

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. 

Bacterial and plant inulin are different not only in molecular weight and in the degree of branching but also in the synthesis and the enzymes applied. Both inulins are synthesized via sucrose. Glucose is generated as by-product. 

Particularly preferred polysaccharides are inulin, levans from plants, and bacterial fructans. Suitable glycol-specific oxidizing agents include sodium periodate, or lead tetra acetate. Examples of reducing agents include sodium borohydride and sodium cyano-borohydride (38). 

Formed by reversion of fructose in strong acid and during hydrol. of inulin. Also by pyrolysis of inulin and bacterial degradn. of inulin with Arthrobacter ureafaciens. Isol. from Lycoris radiata. Cryst. (EtOFO. 

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