Role of amylose in the maintenance of the configuration of rice starch granules

Amylose contents in 39 strains of rice starch, including waxy starch, low amylose containing starch, and non-waxy starch, were measured. Seguchi et al. [1] reported that waxy wheat starch exhibits a ghost appearance by staining and swelling with 25% KI/10% I-2 solution at 25 degreesC. We subjected the 39 rice strains to staining in the same manner. We found that the relative ghost area (%) in a rice starch, which is a measure of granule swelling in 25% KI/10% I-2 solution,, is related to its amylose content (r = -0.78). As the relative ghost area (%) of the rice starch increased rapidly when the amylose content decreased below 5%, we concluded that at least 5% of amylose is required to maintain the structure of rice starch granules. Furthermore, the red-brown central region in ghostly appearing granules decreases with amylose level and the surrounding light brown region increases. When the starch does not contain amylose, the ghost is entirely light brown. The decrease in the area of the red-brown central region with decreasing amylose content suggests that amylose is concentrated in the red-brown central region of the ghost.