Effect Of High Hydrostatic Pressure On Granule Structures Of Maize Starch

Effect of high hydrostatic pressure (HHP) on different structural levels of maize starch granules (i.e., apparent structure, pore and channels, blocklets structure and molecular structure) was studied in this thesis. The combined technology of cubic zirconia anvil cell and Raman spectrum was then applied to explore the structure changes of HHP treated maize starch granules in situ, and discussed the underlying mechanisms.(1) Apparent structural changes in maize starch granules were investigated using scanning electron microscope (SEM).Under a certain starch concentration, as pressure increases, the amount of surface pore structure increases, the size of pores increases, and the degree of granules collapsing also increases. When pressure reaches450MPa or starch concentration exceeds30%, the starch granules begin to swell.(2) The internal pore structural changes of maize starch were investigated by transmission electron microscopy. The granule structure of maize starch broke down from inside out. As pressure increases and starch concentration increases, the amount of starch internal pore structures goes up and pore diameter also goes up. In addition, starch gelatinization degree goes up as pressure increases. The critical pressure leading to changes of starch pore structures, however, decreases as pressure increases.(3) Structural changes of maize starch blocklets were studied using field emission scanning electron microscopy (FESEM). The amount of blocklet was increased firstly, and then decreased as the HHP and starch concentration increases. Moreover, single surface units of blocklets merged to form larger structural clusters and then disperse into small ones as HHP and starch concentration increases. This structural transition is presumably caused by the changed cross-linking between amylopectin clusters.(4) Applying Fourier transform infrared spectrometer (FTIR) led the discovery that O-H stretching vibration, C-OH bond stretching vibration, bending vibration of terminal C, the out of plane bending of C-H and C-0ring breathing vibration were the weakest under600MPa under a constant starch concentration. Furthermore, bending vibration of terminal C remains unchanged under different starch concentrations. C-H bending vibration were affected when pressure reaches300MPa. Under150MPa or450MPa,30%concentration degree, the signal of C-H stretching vibration and bending vibration of C-H bond stretching vibration was the weakest, and the signal of O-H stretching was the strongest. The signal of C-OH bond stretching vibration reach the global maximum under300MPa or600MPa,20%concentration degree.13C CP/MAS NMR spectrum results showed that the peak shape of NO.1-6carbon atoms did not change until300MPa under constant starch concentration. When the pressure reaches450MPa, the chemical shifting of C1, C2, C3, C4and C6shifted to low field, and then to high field as pressure goes up to600MPa. Under constant HHP, the peak shape of NO.1-6carbon atoms changes at150MPa and40%starch concentrations. Moreover, under the pressure of300MPa, the peak shape of C1, C2, C4changed at40%starch concentration, and the shape of C2, C5and C6changed at30%concentration. Under450MPa, the peak shape of NO.1-6carbon atoms changed at30%concentration. Under600MPa, the peak shape of C1, C4changed at30%concentration, and the peak shape of C2, C3, C5and C6changed at40% concentration. The chemical shifting of NO.1-6carbon atoms shifted to low field under150MPa,300MPa or450MPa at40%concentration. As the degree of concentration increased, the chemical shifting changed to high field. The chemical shifting of NO.1-6carbon atoms shifted to low field under the condition of600MPa and20%-40%concentration. When the degree of concentration increased, the chemical shifting changed to high field.(5) The molecular structure changes of maize starch were further investigated using hyphenated techniques of cubic zirconia anvil cell and Raman spectra. Results showed that starch molecules were susceptible to HHP. Compared with other chemical bond in starch molecule, the bonding status of C-O-C in starch molecules is least affected by HHP. It is also demonstrated that Raman shift trend of chemical bond was inconsistent during the process of compression, an indication that the torsion, twisting and stretching in different directions occurred simultaneously in the spatially asymmetric glucose molecules.