Preparation and physical characteristics of resistant starch (type 4) in acetylated indica rice

Early indica rice was chemically modified via acetylation to make modified food starch products with high contents of resistant starch. High contents of RS4 (type 4 resistant starch) of the products were measured. The result showed that the RS4 content increased obviously via acetylation. Acetylated starch was studied by FT-IR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy), XRD (X-ray diffraction) and DSC (differential scanning calorimetry). The starch granules were destroyed as observed by SEM. The X-ray diffraction data showed that the crystal structure of acetylated starch with low degree of substitution changed slightly and a part of crystallite structure (2θ 18°) was destroyed when the acetyl content was more than 3.25%. The heat of crystalloid fusion, gelatinization temperature, and gelatinization enthalpy all decreased (DSC) as the degree of substitution increased. SEM, XRD and DSC indicated that the resistance to enzymatic degradation of acetylated starch depended on the degree of substitution and the integrity of starch granules.