Investigation of Barley Proteins’ Interfacial Properties and Their Applications as Nanoscaled Materials

  • Author / Creator
    Yang, Jingqi
  • The overall objective of this thesis research is to gain fundamental knowledge on the relationship between barley protein molecular structures and their interfacial properties as well as to develop barley protein value-added applications with special emphasis on their utilization as nanoparticles for delivery systems of lipophilic bioactive compounds and electrospun nanofibers. Firstly, the interfacial properties of barley proteins were investigated using B-hordein as a representative. The results revealed that B-hordein had the ability to lower the air-water surface tension to 45 mN/s within 2 h and formed an elastic-dominant film at the interface through intermolecular β-sheets, which stabilized the interface. Compression at the interfacial B-hordein film triggered the conformation and orientation changes of B-hordein. This resulted in the occultation of the repetitive region of B-hordein from aqueous phase, leading to a low digestibility in simulated gastric fluids. Based on this knowledge, barley protein based nanoparticles were successfully developed by high pressure homogenization as a delivery system for lipophilic bioactive compounds. At optimized processing conditions, nanoparticles with regular spherical shape, smooth surface, size of 90-150 nm and zeta-potential of -35 mV were obtained. Barley protein based nanoparticles had less than 2% of the encapsulated bioactive compounds released after incubation in simulated gastric fluids for 2 h and the complete release occurred in simulated intestinal fluids due to pancreatin degradation. Thus, they had potential to protect the encapsulated bioactive compounds in harsh gastric environment, and completely release them in the small intestine, which was the main adsorption site to improve absorption. Barley protein based nanoparticles were resistant to pepsin digestion, had low cytotoxicity and could be internalized by Caco-2 cells. Thus, these barley protein nanoparticles showed strong potential to be used as delivery systems of bioactive compounds for food, pharmaceutical and cosmetic applications. The third and fourth studies explored the opportunity of using barley protein based electrospun fabrics for applications as electrode materials for supercapacitors. Hordein, the major fraction of barley proteins, was electrospun into fibers with zein and lignin. The protein-lignin fibers were then converted into carbon fibers by carbonization at 900°C under argon. The specific surface area was 772 m2/g after activation by CO2 at 800°C for 3 h. These carbon fibers had 3D hierarchical porous structure, high amount (4 atomic%) of nitrogen on the carbon surface and graphene-like nanosheet structures. Such morphology and chemical composition allowed carbon fibers with excellent capacitance of 240 F/g and 31.2 µF/cm2 in 6 M KOH with high cyclic stability. To further increase the nitrogen content, in the last study, calcium acetate was added in the electrospinning solution to form nanofibers with protein, sustain the fibrous structure and generate pores during carbonization. Nitrogen-doped (7%) porous graphitic carbon fibers were derived from protein-Ca2+ fibers through one-step pyrolysis, which was facile and environmentally friendly. Moreover, it was the first time that highly ordered spherical graphitic structure was observed in carbon fibers derived from biomass at relatively low temperature (850°C) without catalysis and corrosive reagents. Based on their structure and chemical features, these carbon fibers had a specific capacitance of 64 µF/cm2 and 98% retention after 5,000 cycles, which was ranking in the most excellent range of carbon fibers reported recently. These carbon fibers have the potential to be used in industrial energy storage systems and personal electronic products.

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    Doctor of Philosophy
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