Starch granules granule structure

Li, J. H., Guiltinan, M. J., and Thompson, D. B. 2006. The use of laser differential interference contrast microscopy for the characterization of starch granule ring structure. Starch-Starke 58 1-5. 

High-Resolution AFM (and LVSEM) Studies of Starch Granule Surface Structure... 

Owing to the method and the type of plasticizer used for TPS production, the process leads to the destruction of the starch granule lamellar structure, giving rise to a quasi-amorphous or semi-crystalline material. 

Amylopectin is a highly branched molecule which is responsible for the main crystalline charactCT of the starch granule. Its structure was modelled as a hyperbranched molecule [17, 51, 52], as proposed initially by Nikuni [53] and French [16] and later improved by Robin [37] (Fig. 15.4). In this model, short chains with 15 D-glucopyranosyl units branch out at almost regular intervals of 25 units to form either external A-chains or internal chains of amylopectin [37]. Starch crystallites are thus formed in compact areas made up of A-chains with DP 15. Less compact areas mainly occupied by B-chains, where the (l,6)-a-D-branching points are located, are placed between these compact areas. 

There are five prime factors that determine the properties of starches 1. starch is a polymer of glucose (dextrose) 2. the starch polymer is of two types linear and branched 3 the linear polymeric molecules can associate with each other giving insolubility in water 4. the polymeric molecules are organized and packed into granules which are insoluble in water and 5 disruption of the granule structure is required to render the starch polymer dispersible in water. The modification of starch takes into account these factors. 

Pea starch granules are oval, sometimes fissured, with a diameter of 20-40 ym (13). Molecular and structural characteristics of the two main components of field pea starch—amylose and amylopectin—are important in determining functional properties (25,26). Smooth field pea starch concentrate contains 97.2% starch of which 30.3-37.8% is amylose (9,23,25-27), and wrinkled pea starch concentrate contains 94.8% starch, which is 64% amylose (26). The gelatinization temperature of smooth pea starch is between 64 to 69 C, and that of wrinkled pea starch is greater than 99 C to 115 C. Gelatinization temperature depends on maturity of field pea seed and amylose content (26,27). 

Starch occurs as highly organized structures, known as starch granules. Starch has unique thermal properties and functionality that have permitted its wide use in food products and industrial applications. When heated in water, starch undergoes a transition process, during which the granules break down into a mixture of... 

FIGURE 5.4 Potato starch granules viewed under polarized light (magnification, x400). Reprinted from Encyclopedia of Food Sciences and Nutrition (Second Edition), Jackson (2003b), Starch - Structure, properties and determination. Pages 5561-5567, with permission from Elsevier. 

Maltese cross (Blanshard, 1979). The crystallinity of starch is caused essentially by amylopectin pol)Tner interactions (Banks and Greenwood, 1975 Biliaderis, 1998 Donald, 2004 Hizukuri, 1996). An illustration of currently accepted starch granule structure is given in Fig. 5.5. It is believed that the outer branches of amylopectin molecules interact to arrange themselves into "crystallites" forming crystalline lamellae within the granule (Fig. 5.5 Tester et al., 2004). A small number of amylose polymers may also interact with amylopectin crystallites. This hypothetical structure has been derived based on the cluster model of amylopectin (Hizukuri, 1986 Robin et ah, 1974 Fig. 5.1). 

FIGURE 5.5 Schematic diagram of starch granule structure. Adapted from Donald et al. (1997), Starch - Structure and functionality, ISBN 0854047425, with permission from Woodhead Publishing Ltd., Cambridge, UK. 

Gelatinization, as we understand now, is not only associated with crystalline order, but is also influenced by structural changes in the amorphous region. XRD does not detect or account for the structural changes that occur in the amorphous regions of the starch granules. 

Blanshard, J. M. V. (1987). Starch granule structure and function A physicochemical approach. In "Starch Properties and Potential" (T. Galliard, ed.), pp. 16-54. John Wiley and Sons, Chichester. 

Buttrose, M. S. (1962). The influence of environment on the shell structure of starch granules. The Journal of Cell Biology. 14,159-167. 

Jane, J.-L. (2006). Current understanding on starch granule structure. /. Appl. Glycosci. 53, 205-213. 

Jenkins, P. J., and Donald, A. M. (1995). The influence of amylose on starch granule structure. International Journal of Biological Macromolecules. 17,315-321. 

Oates, C. G. (1997). Towards and understanding of starch granule structure and hydrolysis. 

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