Starch birefringence

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). 

Birefringence (or double refraction) is the decomposition of a light ray into two rays when it passes through certain types of crystalline material. This occurs only when the material is anisotropic, that is, the material has different characteristics in different directions. Amylose and amylopectin polymers are organized into a radially anisotropic, semicrystalline unit in the starch granule. This radial anisotropy is responsible for the distinctive... 

TABLE 5.1 Comparison of birefringence loss and degree of gelatinization in different starches°... 

Starch Temperature (°C) Loss of birefringence (%) Degree of gelatinization (%) by glucoamylase method... 

Goering, K. Fritts, D. H., and Allen, G. D. (1974). A comparison of loss of birefringence with the percent gelatinization and viscosity on potato, wheat, rice, corn, cow cockle, and several barley starches. Cereal Chem. 51, 764-771. 

Starch gelatinization is the disruption of molecular orderliness within the starch granule. It results in granular swelling, crystallite melting, loss of birefringence, viscosity development, and solubilization. 

Table 3.4 Mean starch granule size, birefringence end-point temperature (BEPT), and x-ray diffraction pattern of 14 maize genotypes 24 day post-pollinationa...

Brown et al.238 reported that starch granules from 18- and 24-day-old su2 kernels are weakly birefringent and have an A-type x-ray pattern (Table 3.4), in contrast to the B-type pattern reported for starch granules from mature su2 kernels.360,387 The BEPT of su2 granules is lower than that of normal granules (Table 3.4).359,388 Based... 

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