Fructans hydrolysis

Polymers of D-fructose are important carbohydrate reserves in a number of plants. Inulins and levans are two major types that differ in structure. D-Fructans require only relatively mild conditions for their hydrolysis, for example, levan was qualitatively hydrolyzed by hot, dilute, aqueous oxalic acid. Permethylated fructans could be hydrolyzed with 2 M CF3CO2H for 30 min at 60°. Fructan oligosaccharides were hydrolyzed in dilute sulfuric acid (pH 2) at 70 (see Ref. 53) or 95° (0.1 M). D-Fructans from timothy haplocorm (where they comprise 63% of the water-soluble carbohydrates) could be hydrolyzed with 0.01 M hydrochloric acid at 98°. 

This enzyme [EC 3.2.1.80] catalyzes the hydrolysis of terminal nonreducing 2,1- and 2,6-linked /S-o-fructofura-nose residues in fructans. 

This enzyme [EC 3.2.1.65], also known as 2,6-/3-D-fructan fructanohydrolase, catalyzes the random hydrolysis of 2,6-j8-D-fructofuranosidic hnkages in 2,6-/3-D-fructans (levans) containing more than three fructosyl units. 

Inulinase (2— l)-/8-D-fructan fructanohydrolase, inulase hydrolysis of (2— l)-/3-D-ffuctosyl links in inulin... 

Fructans in the Jerusalem artichoke are synthesized by the concerted action of two fructosyl transferases that were derived from invertase genes (Van Laere and Van den Ende, 2002). In the initial step (Figure 10.18), the trisaccharide 1-kestose (G-F-F) is synthesized from two sucrose molecules (G-F) in a reaction catalyzed by the enzyme sucrose sucrose fructosyl transferase (SST EC 2.4.1.99). The reaction products are 1-kestose and glucose, and the reaction is essentially irreversible due to the high free energy of hydrolysis (AG = 27.6 kJ-mok1) (Lewis, 1984). 

Inulin is a recognized prebiotic carbohydrate in its own right but is also used as a source of fructo-oligosaccharides by hydrolysis. Inulin, a fructan polymer is widely distributed in plants [264] and chicory Cichorium intybus) is extensively used as a source of inulin for commercial purposes [265]. The roots of chicory contain 15 to 20% inulin and 5 to 10%... 

D-Fructans are hydrolyzed by two D-fructofuranosidases designated hydrolase A and B.203-205 Enzymic hydrolysis breaks only the ft-D-(2 — l)-linkage between a terminal D-fructofuranosyl group and its adjacent, D-fructofuranosyl chain unit as shown in equation 4. 

Sucrose is the sole source for synthesis of D-fructan in artichoke tubers.206 Thus, the level of this disaccharide can play an important role in the regulation of enzyme activities.202,203,207 Sucrose strongly inhibits the enzymic hydrolysis of inulin by D-fructan hydrolases, as... 

The dimeric, cychc anhydrides reviewed by McDonald, and formed during the acetolysis and subsequent hydrolysis of fructans, have now been obtained in much higher yields by the use of fuming nitric acid. However, during these reactions, the fructofuranose form was already present, before ring-closure between adjacent molecules occurred to form the stable ring... 

Bacillus subtilis levansucrase (sucrose 2,6-/8-D-fructan 6-)8-D-fructosyltrans-ferase, EC 2.4.1.10) catalyzes fructosyl transfer from sucrose to levan (154). In the absence of a fructosyl acceptor, the primary reaction is sucrose hydrolysis, although a limited amount of self-initiated levan synthesis occurs as well (155). As with sucrose phosphorylase, acceptor specificity is broad a number of saccharides and other nucleophiles are suitable fructosyl acceptors (154-158). The complete amino acid sequence of the approximately SO-kDa enzyme has been determined by both protein (159) and gene (160) sequence analyses. The three-dimensional structure at 3.8 A reveals a rod- or ellipsoid-shaped protein with a length some four times the diameter (161). 

Fructan is expressed as fructose, after hydrolysis, in leaf segments illuminated for 1.5 hours... 

Most fructans on hydrolysis yield, in addition to D-fructose, a small amoimt of d-glucose, which is derived from the terminal sucrose imit in the fructan molecule. The structure of a typical grass fructan is depicted here ... 

Giger et al. [51] investigated the fructan content of Echinacea purpurea and found that the aerial parts contained ten times less than the roots and that homeopathic tinctures contained fructans with polymerization grades up to 15. It has been suggested to standardize Echinacea purpurea fresh plant preparations on the content of P-l,2-fructofuranosides [128]. The method is based on enzymatic hydrolysis of the fructans by invertase and subsequent determination of fructose by HPLC. Since 3-l,2-fructofuranosides are easily degraded enzymatically during the manu-... 

Hydrolysis of the fructan linkages of sucrose-terminated fructans to lower members and sucrose. 

Two enzymes seem to be necessary for the complete hydrolysis of gluco-fructans one enzyme hydrolyzes fructan units and the other enzyme hydrolyzes the sucrose units (119). 

The rate of hydrolysis of a polysaccharide is a function of its structure. In general, a-n-glycosidic linkages are hydrolyzed more readily than 3-d-linkages. Polysaccharides, such as arabans and fructans, whose sugar units occur as furanosides may be rapidly and completely hydrolyzed under mild conditions, such as in 1 % mineral acid at 80°. Polysaccharides consisting of pentose units in the pyranose form are more resistant, but hot 3% nitric acid causes complete hydrolysis. More concentrated acids, especially hydrochloric acid, decompose the pentoses to furfural. Stronger hydrolytic conditions are necessary for polysaccharides of hexopyranoside units. Usually normal sulfuric or hydrochloric acid at 100° is sufficient, but in certain cases more drastic conditions are necessary. 

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