Wheat starch granule surfaces

X, scale bar represents 3 pm) (b) LVSEM micrograph of a typical region of a Riband wheat starch granule surface. (Magnification 10000X, scale bar represents 3pm)... 

The surface of mature, undamaged wheat starch granules appears to be smooth when viewed with a scanning electron microscope.169,170 Pores and channels are apparent, especially along the equatorial groove of the A granules.173-175 B granules... 

Starch changes during cooking of pasta are reported to vary from a hydration-driven gelatinization process in the outer layer to a heat-induced crystallite melting in the center.525 It is speculated that both the state of the starch and the surface structure contribute to the development of the elastic texture and stickiness of pasta. Interactions between starch and the surrounding protein matrix are evident in the outer and intermediate layer. In the center of cooked pasta, wheat starch granules retain their shape due to limited water diffusion, and the protein network remains dense. 

Greenwell, P., Evers, A. D., Gough, B. M., and Russell, P. L. 1985. Amyloglucose-catalysed erosion of native, surface-modified and chlorine-treated wheat starch granules The influence of surface protein. J. Cereal Sci. 3, 279-293. 

They concluded that these data supported Badenhuizen s17,18 suggestion that starch molecules are completely synthesized in the amyloplast stroma and are then deposited on the granule surface. Once the polysaccharides are part of the granule, there was no evidence of subsequent conversion of amylose to amylopectin.166 This is in contrast to conclusions drawn from long-term 14C-labeling studies of wheat starch.167,168 In results of these studies, amylose appeared to be synthesized first, and then transformed into amylopectin. These differences may be due to the different species used or to the widely different sampling times. 

If amylose and amylopectin are mixed in water, an amylose-rich upper phase and an amylopectin-rich bottom phase are formed. We can regard the starch gelatinisation itself as such a phase separation, where amylopectin remains in the water-swollen granules and amylose forms the outside solution. It is interesting to see how the shape of the granules changes successively during this process, which is illustrated in the case of wheat starch in Fig. 8.6. Thus there is a clear tendency of deformation so as to obtain an outer surface with... 

Nierle, W., El Baya, A.W., Kersting, H.J., and Meyer, D. 1990. Lipids and rheological properties of starch. 11. Effect of granule surface material on viscosity of wheat starch, Starch/Staerke, 42(12), 471. 

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