Using corn, cassava, potato, and sago starches as raw materials, high temperature treatment from 100 to 200 ℃ was adopted to investigate changes in the whiteness of original starches and starches treated with physical methods. Scanning electron microscopy (SEM) was used to observe the granular morphology of potato starch, which had the most obvious change in whiteness. Results showed that, after heating at 200 ℃, the whiteness of potato starch decreased from 85.88 to 45.51, which was the largest change; corn starch whiteness reduced from 88.21 to 79.10, which was the smallest change. After purification by ethanol, the resultant and original starches showed similar changes in whiteness under vacuum heating. At 200 ℃, the largest change in whiteness occurred in potato starch and the whiteness of all starches was lowered by 2 to 6 compared to their respective original starches. After heating under acidic or alkaline conditions, changes in whiteness were more obvious in the native starches, especially under alkaline condition. After heating at 200 ℃, whiteness was reduced to a range of 13.67 to 24.76. When starches were pre-gelatinized and heated, the changes in whiteness were roughly the same for the different starches; whiteness was very close to 39 at 200 ℃. These results demonstrate that the proteins and lipids in starch have little influence on the changes in its whiteness; however, variation in the thermostability of the whiteness of different starches might be related to their granular sizes.
