Study On The Relationship Between Size And Functional Properties Of Starch By Asymmetrical Flow Field-Flow Fractionation

Starch is one of the main energy sources for human beings and is widely used in industrial production,food,medicine and other fields.Starch is a natural polymer which is made of glucose monomers connected byα-(1→4)andα-(1→6)glycosidic bonds.The size distributions of starch granules and molecules range from 1-100μm and 20-250 nm,respectively.The size of starch is one of the most important factors affecting its functional property.Therefore,accurate size characterization of starch is required.In this thesis,the starch granules extracted from three different plant sources(i.e.,rice,sweet potato and lotus seed)were studied.In the first part,a asymmetrical flow-field flow fractionation(AF4)system was developed.Polystyrene(PS)suspensions with different sizes were used to test the separation and characterization performance of the developed AF4device.The results proved that the upper detection limit of developed AF4 device is increased to 20μm.AF4 showed a good resolution for the PS with size in the nano-to micro-scale.On the other hand,the developed AF4 system is easy to disassemble and clean.In the second part,the developed AF4 device,Optical microscopy(OM)and dynamic light scattering(DLS)were employed to characterize the size distribution of starch granules extracted from three different sources.The developed AF4 device is proved to be an accurate and quick method for the separation and size characterization of starch granules.In the third part,commercial AF4online combined with ultraviolet-visible(UV),multiangle light scattering(MALS)and differential refractive index(d RI)detectors(AF4-UV-MALS-d RI)was employed to characterize starch molecules.Meanwhile,scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD)and Differential scanning calorimetry(DSC)were employed to characterize the physicochemical and functional properties of starch(such as molecular weight distribution,particle size distribution,thermal properties,viscosity,digestibility and retrogradation).Finally,the relationships between the size of starch from nano-to micro-scale and its functional properties were studied by Pearson correlation analysis.The size of rice starch granules was significantly positively correlated with T_o(r=0.998,P<0.05)andΔH(r=1.000,P<0.01).While the T_pandΔH of sweet potato starch were significantly positively correlated with starch granule size(r=1.000,P<0.01),and negatively correlated with starch molecular size(r=-1.000,P<0.05),respectively.TheΔH of lotus seed starch was significantly positively correlated with AM/AP(r=0.999,P<0.05).Sweet potato starch presented a significant negative correlation(r=-0.999,P<0.05)between the digestibility with the starch molecule size.No significant correlation between the size of starch with retrogradation property was observed.The results suggested that the sizes of starch granules and molecules were to some extent correlated with their digestibility and thermal properties,which is strongly dependent on their botanical source.In this thesis,the developed AF4 device and commercial AF4-UV-MALS-d RI were used to study the size of starch extracted from three different botanical sources at the nano-to micro-scale.The data obtained in this thesis could be used for the further studying of the correlation between starch size and its functional properties.