Effects Of Complexes Between Fatty Acids And Starch On The Gelatinization And Retrogradation Of Wheat Starch

Starch is made up of amylose and amylopectin. In the presence of fatty acids, amylose could be complexed with fatty acids and a single helix was prepared. The gelatinization and retrogradation of starch would be significantly modified by complexes. Wheat starch with different amylose content, lauric acid, stearic acid and monostearin were mixed by RVA. The effects of fatty acids on the complexing index, gelatinization and retrogradation of wheat starch were investigated. Researches were conducted as follow:The complexing ability of fatty acids and wheat starch were measured by UV-VIS Spectrophotometer and XRD. The results showed that complexing indexes were gradually increased with the increasing amylose content, luaric acid levels and monostearin levels, whereas complex indexes were decreased with the increasing stearic acid levels. The bind ability of lauric acid and wheat starch was the best among the three fatty acids. Luaric acid at 1.5% level had the highest ability to form the complex. The solubility and swelling capacity of wheat starch were increased with the increasing heating temperature and decreased with the increasing amylose content. With the addition of fatty acids, the solubility and swelling capacity of wheat starch were decreased. The crystal structure of wheat starch was A-type. With the addition of fatty acids, x-ray diffraction pattern of wheat starch included V-type peak and the relative crystallinity were gradually increased with increasing complexing index.The gelatinization and textural properties were measured by RVA and TPA. The peak viscosity, holding viscosity and final viscosity were gradually decreased with the increasing amylose content, whereas the pasting temperature and hardness were increased. With the addition of fatty acids, the hardness and holding viscosity of wheat starch were decreased, but the final viscosity were increased. There was no significant change for springiness and cohesiveness. Luaric acid at 1.5% level had the most outstanding effect on the gelatinization and textural properties of wheat starch.DSC and XRD were used to evaluate the effects of fatty acids on the short-time retrogradation of wheat starch. The DSC pattern of samples included the endothermic peak of “typeⅡa” starch-lipid complex, “typeⅡb” starch-lipid complex and amylose recrystallization. The XRD pattern contained V-type and B-type crystalline structure. With the addition of monostearin and lauric acid, the retrogradation enthalpy of amylose and intensity of B-type peak were decreased, whereas the intensity of V-type peak were increased. It could be concluded that the short-term retrogradation of wheat starch was retarded by monostearin and lauric acid.DSC, XRD and TPA were used to evaluate the effects of fatty acids on the long-time retrogradation of wheat starch. The DSC pattern of samples included the endothermic peak of “typeⅡa” starch-lipid complex, “typeⅡb” starch-lipid complex and amylopectin recrystallization. The XRD pattern contained V-type and B-type crystalline structure. With the increasing freeze-thawed cycles, the retrogradation enthalpy of amylopectin, intensity of B-type peak and hardness of wheat starch gel were increased, but the springiness and cohesiveness were decreased. With the addition of monostearin and lauric acid, the retrogradation enthalpy of amylopectin, the intensity of B-type peak and hardness of wheat starch gels were reduced, whereas the intensity of V-type peak, springiness and cohesiveness were increased. It could be concluded that long-time retrogradation of wheat starch was promoted by the repeating freeze-thawed cycles and retarded by monostearin and lauric acid.