Atomic Force Microscopy Investigation of Disorder Process on Rice Starch Granule Surface

Starch - Starke (Impact Factor: 1.22). 01/2006; 58:475–479. DOI: 10.1002/star.200500471

ABSTRACT Precise ultra-structures of rice starch granules have been analyzed by atomic force microscopy combined with a structure-disorder process at ambient conditions. Atomic force microscopy is a useful technique to obtain images under atmospheric condition with a nanometer-scale resolution. The images obtained by a high-resolution tapping mode revealed a detailed surface ultra-structure of native rice starch granule with a diameter of approximately 100 nm. The ultra-structures were arranged in series like a chain, and the chain was bundled together into a rod or larger column. After a disorder process using plasticizing/lyophilization of the granules, a significant change in the organization of the surface morphology was detected. Some fine particles of approximately 30 nm in diameter were observed, which might correspond to the individual single cluster in the crystalline region of the starch granule.

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    ABSTRACT: Wheat starches at different stages of maturities were evaluated for their iodine absorption properties by measuring the ratio of absorption to reflection spectra (K/S) and crystalline structure by using wide angle X-ray scattering (WAXS). The surface of starch granules was also visualized by using atomic force microscopy (AFM). The K/S spectral data demonstrated different levels of mobility of starch polymers at different stages of maturity and the mobility of longer chain polymers with increasing moisture contents. Iodine did not change the characteristic A-type crystalline pattern. However, the extent of effect of iodine on starch crystallinity was affected by maturity and moisture content of starches. AFM images of iodine exposed starches supported the interaction of iodine molecules with starch polymers. Differences in surface features were observed for different maturities.
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    ABSTRACT: Starches from normal rice (21.72% amylose), waxy rice (1.64% amylose), normal corn (25.19% amylose), waxy corn (2.06% amylose), normal potato (28.97% amylose) and waxy potato (3.92% amylose) were heat-treated at 100 °C for 16 h at a moisture content of 25%. The effect of heat-moisture treatment (HMT) on morphology, structure, and physicochemical properties of those starches was investigated. The HMT did not change the size, shape, and surface characteristics of corn and potato starch granules, while surface change/partial gelatinization was found on the granules of rice starches. The X-ray diffraction pattern of normal and waxy potato starches was shifted from B- to C-type by HMT. The crystallinity of the starch samples, except waxy potato starch decreased on HMT. The viscosity profiles changed significantly with HMT. The treated starches, except the waxy potato starch, had higher pasting temperature and lower viscosity. The differences in viscosity values before and after HMT were more pronounced in normal starches than in waxy starches, whereas changes in the pasting temperature showed the reverse (waxy > normal). Shifts of the gelatinization temperature to higher values and gelatinization enthalpy to lower values as well as biphasic endotherms were found in treated starches. HMT increased enzyme digestibility of treated starches (except waxy corn starch); i.e., rapidly and slowly digestible starches increased, but resistant starch decreased. Although there was no absolute consistency on the data obtained from the three pairs of waxy and normal starches, in most cases the effects of HMT on normal starches were more pronounced than the corresponding waxy starches.
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