Starch polarized light

Starch granules, when observed imder polarized light, exhibit an optical birefringence pattern known as a "Maltese cross" (Fig. 5.4), which implies a high degree of molecular order within the granule (Greenwood, 1979). 

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. 

Lastly When viewed with polarized light the cross is generally less regular in the potato starch grains than in those of the tous-les-mois.—Pereira. 

Figure 5.1 Raw starch granules observed by scanning electron microscopy (a) potato (b) cassava and (g) rice starches. The corresponding granules under polarized light are shown in insets. Lowest figure shows SEM of in situ granules in potato parenchyma cell. (Reproduced with permission from reference 1)...

Figure 6.2 Morphological evolution of maize starch granules in floury endosperms of normal maize (A76) and high-amylose maize (A62 and A36) during maturation from the fifteenth to the 72nd day after anthesis, as seen under polarized light. Note that the filamentous starch granules of the high-amylose maize show Maltese crosses only in some nucleations. Percentages are amylose contents during maturation.14...

C. Examine a portion of the sample with a polarizing microscope in polarized light under crossed Nicol prisms. The typical polarization cross is observed, except in the case of pregelatinized starches. 

Starch granules vary in size, shape, composition, and properties (Table I), and they are a semicrystalline material. Because the starch granule has a high degree of order, when viewed in polarized light it shows birefringence, the maltese cross of Fig. 1. 

FIG. 1. The birefringence (maltese cross) shown by maize starch illuminated with polarized light, 700x. From Fitt and Snyder (1984). 

Butanone moderately alters the characteristics of gelation of potato starch and significantly changes the appearance of granules under normal and polarized light.683 684... 

Temperature versus enthalpy profiles similar to those shown in Figure 4-15 are obtained when starches are heated either in excess water, that is, when water stareh ratios are equal to two or greater, or under intermediate water content. The start of the endothermic peak at To corresponds to loss of birefringence, in the form of the typical Maltese cross, when the starch granule is viewed under polarized light. A single endotherm, such as that obtained under excess water conditions, is referred to as the... 

When unmodified starch granules are observed using polarized light, two dark lines will form a cross or a V-shape (Fig. 4). The shape of the cross can be... 

Wheat starch was previously gelatinized by heating an aqueous suspension for 15 min at 80°C. Gelatinization was confirmed by observation under polarized light microscopy. 

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