Starch grains of wheat considered as partially dehydrated amylose.

Abstract

Alsberg and Perry 1 have shown that about 60 per cent of the starch grains is soluble in cold water if it is ground for several days in a pebble mill. This fact will be used in this paper as a basis for an explanation of the properties and structure of wheat starch grains. The assumption that amylose occurs in starch grains in different stages of dehydration proved to be the most satisfactory working hypothesis. We will assume the grains to be built up of alternate layers of more hydrated amylose (less refractive rings) and of less hydrated amylose (refractive rings, to which belongs the surface ring). If we follow the terminology of Meyer, without accepting his theory in detail, the former, β-amylose, is not only soluble in hot water, but also in cold water; the latter, α-amylose, is not soluble in boiling water at 100° C. Of the α-amylose rings, the surface ring is the denser and the more dehydrated. It has a low swelling capacity at room temperature. Though the inner layers, being less dehydrated, tend to have a higher water content and to elongate their circumference, the surface ring does not allow this. In this way, there exists an equilibrium between the swelling capacity of the inner layers and the cohesion (elasticity) of the surface layer. If the cohesion of this border layer is decreased or destroyed (by damaging), the equilibrium is broken and more water can be taken in. If this cohesion is decreased in additional α-amylose rings, greater swelling occurs, and β-amylose leaches out; if the cohesion is destroyed in still more rings (by damaging), all the β-amylose dissolves and diffuses out. The last phenomenon is caused by grinding, by which all the α-amylose rings are crushed and their continuity broken, so that the β-amylose, or 60 per cent of the total starch grains, goes into solution in the surrounding water.