Abstract: The morphological change of starch granules in tapioca starch and xanthan gum during gelatinization process was observed by light microscope (LM) and scanning electron microscope (SEM). The starch gelatinization was an interaction process between starch and water. A low-field NMR technique was used to observe the dynamics of water molecules in biopolymer system. The leakage amount of amylose was measured to monitor the mobility of starch chain. According to spinspin relaxation time (T2) of dynamic water molecule during gelatinization process, the gelatinization mechanism of tapioca starchxanthan gum system was explored. Results indicated that xanthan gum exhibited a reduction of swelling power in tapioca starch. Uniform dispersed steric hindrance was observed in starch granules through LM and SEM. Meanwhile, tapioca starch granules well dispersed in xanthan gum through the observation of SEM. Xanthan gum increased gelatinization temperature and the stability of tapioca starch, which was due to inflection point from 50 to 60 ℃ and higher T2 at 95 ℃. Mobility of starch chains were reduced due to the addition of xanthan gum, which could be explained by the declined leakage of amylose.

Key words: tapioca starch, xanthan gum, water, gelatinization, mechanism