Mechanical activation effects on crystal structure and chemical reaction activity of maize starch
Maize starch was mechanically activated by a stirring-type ball mill.The effects of mechanical activation on crystal structure,thermal properties,granule shape and particle size of maize starch were examined by means of X-ray diffraction,differential scanning calorimetry,scanning electron microscope and particle size analyzer.Moreover,mechanically activated maize starch(MAMS)with different activation times was acetylated with acetic anhydride and graft-copolymerized with acrylamide under the same experimental conditions.The mechanical activation effects on chemical reaction activity of maize starch were investigated by analyzing the influence of mechanical activation on degree of substitution(DS)of esterification and grafting rate(G)and grafting efficiency(GE)of graft copolymerization.The results indicated that the DS,G and GE of MAMS were higher than that of native starch,and showed obviously enhanced chemical reaction activity of maize starch by mechanical activation.The crystal structure and compact granule surface of maize starch were destroyed by mechanical activation,and the crystallinity decreased from polycrystalline to amorphous.With increasing activation time,the gelatinization temperature and pastes viscosity of MAMS decreased and its fluidity was enhanced.As a consequence,the resistance of reagents diffusing into starch solution would be reduced and it was easier to diffuse into starch intramolecule.