Preparation, Structure and Properties of High-Amylose Maize Type Ⅲ Resistant Starch

Using high-amylose maize starch G50 and G70 as raw material, type Ⅲ resistant starch was obtained by successive steps of acid hydrolysis, pasting, debranching and recrystallization, and annealing and autoclaving treatments were used to improve the yield of resistant starch. Scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), rapid viscosity analysis (RVA) were used to evaluate the morphology, crystalline structure, thermal properties and pasting properties of starch granules, and the digestion properties of starch were tested by the Englyst method. The results showed that the yields of type Ⅲ resistant starch from high-amylose maize starch G50 and G70 after acid hydrolysis were 77.9% and 84.5%, respectively, and were reduced to 54.4% and 70.2% after recrystallization, respectively. For G50 and G70, the morphology of starch granules was destroyed after modification, and aggregates with different sizes and irregular shapes were formed. The crystalline type of starch changed from B + V to A + V, and the crystallinity increased. The pasting temperature of starch increased, and the viscosity almost disappeared after heating. The solubility of G50 and G70 significantly increased after acid hydrolysis, pasting, debranching and recrystallization, while the solubility and swelling power of type Ⅲ resistant starch decreased after annealing and autoclaving treatments. In vitro digestion tests showed that the modified G50 and G70 had stronger resistance to digestion than the raw ones, and the resistant starch content of G70-derived type Ⅲ resistant starch autoclaved after addition of 20% water was the highest (80.5%). In conclusion, the modification treatment can effectively increase the content of resistant starch in high-amylose maize starch G50 and G70, and the content of resistant starch is significantly positively correlated with the crystallinity and pasting temperature.