Crystalline dextrins

Schardinger intended to continue his work on these crystalline dextrins in the hope that they might shed some light on the processes of starch synthesis and degradation, or on its composition. However, when, after a long suspension, he again took up work in this direction, the strain used... 

Although Schardinger did not propose a structure for his crystalline dextrins, he made several observations that can now be attributed to their cyclic structure. For example, he discovered their ability to engage in complex-formation "With various substances, the crystalline dextrins form loose complexes which, like those produced with alcohol, ether, and chloroform, are indeed partly decomposed by water, while the iodine complexes are more stable toward water. He also found, as previously mentioned, that the crystalline dextrins were nonreducing toward copper salts and nonfermentable by yeast. This last observation he considered was "... the most essential thing that I was able to mention concerning the formation of crystalline dextrins by microbes. Both of these observations can be explained by the lack of a chain termination. 

Schardinger brought his work on the crystalline dextrins to a close in 1911. He ended his work with the statement I realise that still very many questions remain unsolved. The answer to these I must leave to another, who, owing to more favorable external conditions, can deal with the subject more intensively. It was to be another twenty-five years before the cyclic nature of Schardinger s dextrins was recognized. 

The several nonroducing crystalline dextrins obtained by Schardinger through the action of B. macerans on starch have long been a source of... 

While the enzymic approach must be refined and rationalized, present evidence is completely in accord with the concept of linear and branched structures for the two starch components. The theory has been advanced that the individual alpha and beta Schardinger dextrins originate from specific starch fractions, but this appears to be untenable. No satisfactory mechanism has been proposed to account for the production of the several crystalline dextrins. 

About 25-30% of the starch is converted to crystalline dextrins. Amorphous dextrins are also produced. 

The crystalline dextrins are precipitated from aqueous solution by alcohol as well as by ether, chloroform, or iodine solution. They are nonreducing to copper reagents and non-fermentable by yeast. 

In his closing paragraphs on the crystalline dextrins Schardinger notes I realize that there are many questions which have not yet li)een answered. I must leave the answering of them to the person who, thanks to more favorable circumstances, can engage himself more intensively with the subject. ... 

The hitherto undescribed y-dextrin appeared in the fractionation, although it was probably contaminated with other dextrins. Fractions 5 and e do not represent homogeneous materials most likely they are mixtures of the crystalline dextrins with amorphous limit dextrins (see Scheme III). 

Although the Tilden-Hudson test is very useful it has certain drawbacks in precise work, (a) The exact time at which needles appear is difficult to determine, (b) Enzyme activity is slowed but not stopped by the addition of iodine solution in fact, it is possible to add starch to a mixture of enzyme and iodine solution and observe the gradual formation of the crystalline dextrin-iodine complexes, (c) The apparent activity depends very much on the presence of such foreign materials as salts, n-glucose, maltose, etc., which may be present in the enzyme solution. In some enzyme preparations which seem to have fair activity, the needles are never observed. 

In comparative studies of starch fractions, Wilson, Schoch and Hudson, and also Kerr, - showed that the amylose fraction of starch gave much higher yields of Schardinger dextrins (up to about 70 %) than did the amylopectin fraction. Starch modification or degradation products in general gave reduced yields especially with beta amylase limit dextrins or acid hydrolyzed starch sirups there was no detectable production of crystalline dextrins. 

Schardinger himself did not attempt molecular-weight determinations of the crystalline dextrins. The first molecular-weight determinations were based on freezing-point depressions in water" or on osmotic-pressure measurements. " " Other measurements were based on dialysis rates or on cryoscopic measurements rvith the acetates," nitrates, and methyl ethers. In some cases microisopiestic methods were used."-... 

The first reference to cyclodextrins was published in 1891 by the French scientist A. Villiers. He described the isolation of 3 g of crystalline substance from bacterial digest of 1000 g of starch [7]. He named the substance cellulosine , assuming that this substance is some sort of cellulose. Soon after, the Austrian microbiologist F. Schardinger isolated two crystalline compounds from bacterial digest of potato starch. He named these compounds crystalline dextrins and later changed the names to a-dextrin and P-dextrin [8], In 1935, Freudenberg and Jacobi discovered y-cyclodextrin [9]. 

Later, Schardinger found that one of the thermophilic bacteria, which he called strain 11 was able to dissolve starch and form crystalline dextrins [4]. Although Schardinger did not propose a structure for his crystalline dextrins, he made several observations regarding their cyclic structure. One of his important findings was that With various compounds, the crystalline dextrins form loose complexes" [4]. 

An extracellular enzyme is present which decomposes starch to a crystalline dextrin. 

Preparation of Macerans Amvlase. Macerans amylase was separated from cultures of Bacillus macerans in 1939 by Tilden and Hudson (35). The enzjnmatic hydrolysis of starch by this organism and the detection of the crystalline dextrins was first reported by Villiers... 

Preparation of Cyclic Dextrins bv Acetylation. Other methods for isolating the cyclic dextrins have been used. An early procedure utilized the differences in solubilities of the dextrin acetates (45). An enzymolysate of starch and macerans amylase was prepared by methods similar to those described above. The cyclic dextrins were precipitated from this enzymolysate with a complexing agent and the dextrin complexes which formed were collected by filtration and air-dried. The mixture of dextrins was acetylated with acetic anhydride in pyridine. A preferential crystallization of the dextrin derivatives was used to separate the derivatives and the individual dextrin acetates were obtained. Deacetylation of the derivatives is required to obtain the crystalline dextrins. 

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