The properties of amylose as related to the fractionation and subfractionation of starch

Factors which infulence the apparent molecular size of amylose are discussed. The effect of various isolation procedures on the molecular size of the amylose from potato starch has been studied. Degradation occurs when sulphur dioxide saturated water is used to extract the granules; a method involving 0.01 M mercuric chloride is recommended. The properties of the amylose obtained on aqueous leaching of the granule are controlled by the pretreatment of the granules. This behaviour has been studied in detail. When a granular starch is treated with boiling 80 % aqueous methanol, leaching results in the extraction of a subfraction of amylose which is hydrolysed completely to maltose under the action of β‐amylase. Other procedures involving the action of boiling organic solvents on potato and wheat starches have been critically examined; degradation and modification of the properties of the amylose may then occur. The gelatinization of pretreated granules has been examined. A series of subfractions of amylose has been obtained from barely and potato starches by leaching successively with water at increasing temperature; the amylose remaining in the residual granule was then obtained by complete dispersion. These subfractions showed an increase in moleculare size (by viscosity measurements) which was accompanied by a decrease in the percentage conversion to maltose on β‐amylolysis. The implications of these results with regard to the structure of amylose are discussed. Various methods for swelling granules prior to dispersion have also been examined; pretreatment with liquied ammonia was found to be most satisfactory for aiding dispersion. The method of fractionation of potato starch by treating the granules with alkali has been studied.