Plant protein gel formation mechanisms and their applications as delivery systems of bioactive compounds

• Author / Creator

  Yang, Chen

• The objective of this research was to understand the gel formation mechanisms of plant proteins by both heat- and cold-induced methods, and use the knowledge gained to design plant protein gels with improved mechanical properties for food applications and as nutraceutical delivery systems. In the first study, the formation mechanisms and properties of heat-induced canola protein gels were investigated. At low pH and temperature, the gels exhibited randomly aggregated particulate fractal network structures, while at high pH and temperature, the macro-porous dense wall network structures were established. The protein conformational study and gel dissociation test suggested that the higher heating temperature and pH induced more unfolded structures through splitting inter- and intra-chain disulfide bridges so as to facilitate the establishment of molecular interactions. Remarkably, the macro-porous dense wall structure exhibited much stronger gel strength than the gel with particulate fractal structure. In the second study, cold-set oat protein gels possessing a percolating network structure were prepared using glucono-δ-lactone (GDL) as an acidification agent. The polymer-like percolating structures were established by active oat protein monomers as small building block units through abundant cross-linking points. By increasing the GDL concentration, more intra-floc linkages and greater particle volume fractions were created at the supramolecular level, resulting in a dense rough gel wall with superior mechanical properties. In particular, gel formed with 10% GDL that exhibited compact network structure with small pores and a thick wall had an excellent water-holding capacity (90%) and comparable mechanical strength to egg white gel. Moreover, the cold gelation has provided the opportunity for oat protein gels to be used as delivery systems of heat labile active compounds, as the gels can be formed at ambient temperature. Accordingly, in the third study, novel core-shell beads were developed from oat protein in combination with shellac via a cold-gelation method at ambient temperature. The optimized sample showed a homogeneous, smooth and integrated shell structure stabilized by hydrophobic interactions between oat protein and shellac. In vitro tests in the simulated gastro-intestinal tract indicated that the beads could effectively prevent premature diffusion of the contained riboflavin, and protect L. acidophilus and amylase in the harsh environment of gastric fluids at low pH with pepsin. When transferred into the simulated intestinal tract, riboflavin and L.acidophilus were sustainably released to exert health benefits. Finally, oat protein-shellac nanoparticles with controllable sizes ranging from ~ 90 to 300 nm were fabricated by the cold gelation method for delivery of resveratrol. These nanoparticles exhibited regular spherical shapes, good colloidal stability and high encapsulation efficiencies of up to 90%. In vitro tests showed that the resveratrol uptake and transport could be increased 7.2 and 12.9 times, respectively, compared to free resveratrol. In vivo test in rat models demonstrated that the nanoparticles could significantly improve the oral bioavailability of resveratrol and prevent the CCl4-induced hepatotoxicity by reducing oxidative stress of the tissue. This research has advanced fundamental understanding of canola and oat protein gelling mechanisms in controlling gel microstructures and mechanical properties, which has laid a good foundation for applying this knowledge in developing novel gelling gredients of plant origin. The novel beads and nanoparticles based on oat protein were fabricated at ambient temperature without using organic solvents; thus they have good potential to be developed into delivery systems of bioactive molecules to create functional food ingredients for improvement of public health.

• Subjects / Keywords

  • Bioactive compounds
  • Probiotics
  • Nanoparticles
  • Oat protein gel
  • Gelation mechanisms
  • Gel mechanical properties
  • Canola protein gel
  • Nutraceutical delivery system

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3D50G891

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.