The molecular composition and physical aspects of starch structure are examined in relation to starch properties and utility. The structures and molecular properties of amylose and amylopectin are further considered for their effects on properties of starch granules and pastes, and whether or not they act independently or in concert with one another. Discussion of amylopectin focuses on models featuring clusters of short chain molecules that are interlinked and regularly spaced. Low and wide angle X-ray diffraction studies are cited to confirm the cluster model and the role of amylopectin in starch crystallinity. The diversity of starch is evident by its depostion in one or more sites within a plant and by the variety of plants in which the starch is found. In addition, starches differ widely in size, shape and composition.

The structures and transformations of the starch crystal forms A, B, C and V are reviewed from the viewpoint of their industrial importance. Reviewed also is the non‐crystalline or amorphous state of starch and its role in determining the physical properties of native and gelled starches.

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SynopsisOriented amylose fibers in the V form were prepared and subjected to x-ray analysis. Unit cells and the probable space group of Pf21%'121 were determined for the V anhydrous and V hydrate forms of amylose; the analysis confirms previous predictions of these structures based on x-ray powder patterns. Chain folding in V amyloses is discussed in view of crystallographic evidence and folding experiments conducted with space-filling models. Reported also is evidence for amylose helices having diameters intermediate between 13.0 and 13.7 A.