Structure of the Starch Granule.

The purpose of this paper is to present an hypothesis regarding the anatomical1 structure of natural starch granules. The hypothesis itself is not new; it is a combination of parts of older hypotheses, but with the introduction of some concepts new for starch, though not new in themselves. The hypothesis, reduced to its simplest terms, will first be stated without proofs at the risk of biasing the reader against it. The physical properties of granules, so far as pertinent, will be examined to determine whether the hypothesis is useful for understanding them. The hypothesis is based on certain observations recorded in the literature or newly presented here. These observations are: 1. The starch granule may be made to swell and shrink by varying its water content. 2. At ordinary temperatures, swelling in water is limited; at higher temperatures, it is great and may lead to ultimate dispersion of most of the granule substance (gelatinization). 3. The granule, if mechanically injured, i.e., if it is chipped or cracked, swells greatly in cool water at the site of injury, and only there. 4. The granule is insoluble in cold water. 5. The granule, if mechanically injured, is more or less soluble in cool water by partial dispersion of the swollen portion. 6. The natural granule consists-at least in large measure-of material in orderly arrangement and exhibits a characteristic x-ray diagram. The diagram may be changed by causing the granule to swell, and under some circumstances the process upon which the change in diagram depends is reversible. 7. Completely anhydrous starch exhibits no x-ray diagram. 8. Thoroughly ground-up and mechanically disintegrated starch exhibits no x-ray diagram.