Starch cyclodextrins from

Figure 4.15 Selective adsorption synthesis of a-cyclodextrin from starch applying a hatch process using a sequence of stirred-tank reactor, heat exchanger modules and adsorption step...

CGTases (EC 2.4.1.19) are bacterial enzymes that facilitate the biosynthesis of cyclodextrins from starch through intramolecular transglucosylation. The primary structures of most of these enzymes have been published, and the three-dimensional structure of Bacillus circulans CGTase has been established. Studies of transglucosylation molecular mechanism have indicated that amino acids such as histidine and tryptophan are implicated in such mechanisms. Nitration of CGTase with TNM induces a loss of enzyme activity, a decrease in enzyme affinity towards the (i-CD copolymer, and a loss of tryptophan fluorescence (Villette etal. 1993). 

The use of chiral stationary phases (CSP) in liquid chromatography continues to grow at an impressive rate. These CSPs contain natural materials such as cellulose and starch as well as totally synthetic materials, utilizing enantioselective and retentive mechanisms ranging from inclusion complexation to Ti-electron interactions. The major structural features found in chiral stationary phases include cellulose, starch, cyclodextrins, synthetic polymers, proteins, crown ethers, metal complexes, and aromatic w-electron systems. 

They are prepared by enz3miatic degradation of starch. The enzyme cyclodextrin glucanosyltransferase (CGT) from Bacillus macerans. Bacillus megaterium or other bacterial strains cut the starch helix and join both ends of such destruct forming a cyclic compound. Because enzymes are not very specific, the obtained mixture contains cyclodextrins from 6 to 12 glucose units. The main fi-actions are a-, p- and y-cyclodextrins which correspond to 6, 7 and 8 glucose units. 

Low-cost production of cyclodextrins from starch, guar gum hydrolysis, treatment of pectin-containing effluent, production of wheat and rice straw... 

Kim, TJ, YD Lee and HS Kim (1993). Enzymatic production of cyclodextrins from milled corn starch in an ultrafiltration membrane bioreactor. Biotechnology and Bioengineering, 41, 88-94. 

Cyclodextrins are macrocyclic compounds comprised of D-glucose bonded through 1,4-a-linkages and produced enzymatically from starch. The greek letter which proceeds the name indicates the number of glucose units incorporated in the CD (eg, a = 6, /5 = 7, 7 = 8, etc). Cyclodextrins are toroidal shaped molecules with a relatively hydrophobic internal cavity (Fig. 6). The exterior is relatively hydrophilic because of the presence of the primary and secondary hydroxyls. The primary C-6 hydroxyls are free to rotate and can partially block the CD cavity from one end. The mouth of the opposite end of the CD cavity is encircled by the C-2 and C-3 secondary hydroxyls. The restricted conformational freedom and orientation of these secondary hydroxyls is thought to be responsible for the chiral recognition inherent in these molecules (77). 

Low cholesterol egg products are formed by extraction of cholesterol from the egg. Attempts have been made to extract cholesterol by using hexane or by supercritical CO2 extraction methods (24,25). A whole egg product in which 80% of the cholesterol is removed by a process using beta-cyclodextrin, a starch derivative, added to egg yolks has been introduced. The cyclodextrin binds up to 80% of the cholesterol, the mixture is centrifuged, and the Hquid separated. The cholesterol-reduced yolk is then blended with egg white, pasteurized, and packed in asceptic containers to give a Hquid whole egg product having a shelf Hfe of 60 days under refrigeration (see Eood packaging). 

The first report in the literature of the isolation of a substance recognizable as a cyclodextrin was that of Villiers which appeared in 1891. From digests of Bacillus amylobacter on potato starch, Villiers obtained a small amount (3 g per 1000 g of starch) of a crystalline material, which he named cellulosine because of its resemblance in some respects to cellulose. The foundations of cyclodextrin chemistry were laid down, however, in the period 1903-1911 by Schardinger, and, in fact, some of the older literature frequently refers to the cyclodextrins as Schardinger dextrins. 

Prior to 1939, however, it was not known whether the cyclodextrins were products of the synthetic metabolism of Bacillus macerans, and therefore, perhaps, quite different from the components of starch, or whether they were formed by a single enzyme and therefore closely related to the starch structure. Then, Tilden and Hudson announced the discovery of a cell-free enzyme preparation from cultures of Bacillus macerans which had the ability to convert starch into the Schardinger dextrins without the production of maltose, glucose, or any other reducing sugars. They thus concluded that the Schardinger dextrins were either the true components of starch or closely related to such true components. 

Mol. weight (xlO Optimum pH pH stability Optimum temp. Thermostability Isoelectric point Product from pullulan from starch Activator Inhibitor Cyclodextrin (B- and y-)... 

Starch Liquefaction with a Highly Thermostable Cyclodextrin Glycosyl Transferase from Thermoanaerobacter Species... 

Variations of this method are possible in several ways. First of all, cyclodextrin which is available on a large scale by enzymatically catalyzed modification of starch can be tailored by chemical reactions. Furthermore, copolymerizations between different host-guest complexes are possible whereby in some cases the reactivity ratios differ from those reported in literature. 

Cyclodextrins are cyclic maltooligosaccharides available by enzymatic syntheses from starch. Due to their easy access, sulfated cyclodextrins had been investigated back in the early 1960s for their plasma clearing activity [53]. More recently, the activities of -cyclodextrin (cycloheptamaltaose,)3-CD) tetradecasulfate (24) were evaluated in more detail. It was prepared by sulfetion of -CD which led to the sulfation of the primary and one of the secondary hydroxyl groups per pyranose ring so that a mixture of differently sulfated compounds resulted (Structures 7). 

Bender, H., Siebert, R., Stadler-Szoke, A. (1982). Can cyclodextrin glycosyltransferase be useful for the investigation of the fine structure ofamylopectins Characterisation of highly branched clusters isolated from digests with potato and maize starches. Carbohydr. Res., 110,245-259. 

In 2002, Do et al. [85] proposed a pathway for the enzymatic synthesis of (-)-menthyl a-maltoside and a-maltooligosides from (-)-menthyl a-glucoside using cyclodextrin glucanotransferase obtained from Bacillus macerans. The reaction can be performed in a reactor containing (-)-menthyl a-glucoside, the enzyme and soluble starch the yield was about 80% 15% (-)-menthyl a-malto-side and 65% (-)-menthyl a-maltooligosides, respectively. Treatment of the starch with a-amylase can raise the proportion of (-)-menthyl a-maltoside. 

Among enzyme modified starch derivatives,cyclo dextrins behave as empty molecular capsules with the ability to entrap guest molecules of appropriate geometry and polarity.The included molecules are protected from surroundings light, heat,oxidation, etc. The flavor cyclodextrin com -plexes show the above advantageous properties while they are in the dry,solld state.On contact with water,cyclodextrin complexes release their flavor content. In Hungary,the spice flavor beta-cyclodextrin complexes have been on the market, since 1982. 

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