Study On Physicochemical Properties Of Wheat Starch-fatty Acid Complexes

Starch is constituted of amylose and amylopectin, starch and fatty acid molecules would formhelical complexes by hydrophobic interaction under some conditions, while the internal structureof amylose was occupied by fatty acid. Starch-fatty acid complexes affect the solubility, swellingcapacity, rheological properties, gelatinization, thermal and retrogradation properties of starch.Effect of fatty acid on physicochemical properties of wheat starch was investigated. In thisstudy, we used wheat starch as a raw material, mixed wheat starch with lauric acid，myristic acid，palmitic acid, stearic acid and oleic acid to form starch-fatty acid complexes. The absorbance andcomplexing index of starch were measured. The pasting properties, crystalline structures, thermal,texture properties and freeze-thaw stability of complexes were investigated by Rapid ViscosityAnalyzer (RVA), X-ray diffraction（XRD), Differential Scanning Calorimetry(DSC) and TextureProfile Analysis(TPA).The results showed that: X-ray diffraction pattern of wheat starch-fatty acid complexeschanged from A-type to V-type; the complexing index(CI) of wheat starch-lauric acid complexwas highest. The (CI) was decreased with the carbon chain length of fatty acids increased andincreased with the fatty acids content increased.Research on change of properties between wheat starch and complexes showed that, additionfatty acids has significant effect on pasting properties of wheat starch, compared with the controlgroup, the peak viscosity, holding viscosity, breakdown decreased, while the final viscosity andsetback were increased, which lauric acid showed the most significant effect on pasting propertiesof wheat starch.The DSC showed that addition the lauric acid, myristic acid, palmitic acid decreased thevalues of onset temperature, peak temperature and end temperature，while the stearic acid andoleic acid increased the To, Tpand Tc, the enthalpy of five complexes were significantly reduced.The starch-fatty acids complexes were Ⅱ-type. The pyrolysis temperature of complexes are morethan110℃. The pyrolysis temperature was decreased with increase of carbon chain length.The repeated freeze-thaw cycles to wheat starch result in syneresis. The forms of starch-fattyacid complexes delayed the development of a spongy matrix, inhibited the precipitation of watermolecules, reduced the syneresis rate and improved the freeze-thaw stability of wheat starch.The texture properties of starch gel were closely related to food quality, also as an important indicator of food quality. Starch occurs in varying degrees of retrogradation during storage,resulting in a decline in food quality. TPA experiments showed that with the extension of storagetime, the hardness, chewiness of starch were increased; the springiness and cohesiveness weredecreased. Compared with the control group, the wheat starch which added with fatty acid showedlower hardness, lower chewiness and higher springiness, higher cohesiveness. These resultssuggest that addition of fatty acid is effective to improve texture properties and reduceretrogradation of starch.