Older Methods of Starch Fractionation

This survey will compare the various modes of starch fractionation, with particular emphasis on selective precipitation methods recently developed in these laboratories. The evidence for linear and branched structures of the fractions will be discussed, and the behavior of starch and its various modifications will be interpreted on that basis. 

The heterogeneity of starch was recognized in the early literature by such investigators as Guerin-Varry (1834-36), Naegeli (1862-81), 

Use of poor quality or degraded starches in experimental investigations. 

Inadvertent degradation of the starch through drastic chemical treatment. 

Difficulties in dispersing starch to give homogeneous sols, due to persistence of the swollen granule. 

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Older methods of fractionating protein admixtures in aqueous solution usually involved the stepwise addition of ammonium sulfate, or an organic solvent, such as acetone or ethanol. These methods have been used in the crystallization of several starch-metabolizing en-... 

The nomenclature of starch components has become highly confused through the indiscriminate use of such terms as a and /3-amylose, amylose and amylopectin, amyloamylose and erythroamylose, etc. It does not seem advisable to apply any of these older terms to the new and unique fractions obtained by selective precipitation methods. It is therefore proposed that the term A-fraction be applied to that portion of the starch which is preferentially precipitated by various alcohols or by higher fatty acids, and which exhibits a high affinity for iodine. Correspondingly, the residual non-precipitated portion of the starch, which possesses low iodine affinity, is termed the B-fraction. These designations apply to laboratory-prepared samples, and do not carry any a priori connotations of purity, homogeneity, or structure. 

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