Zixiang Liu | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Zixiang Liu. This seminar is open to the general public to attend.
Thesis Topic: Pressurized Gas eXpanded (PGX) liquid drying of sodium alginate and its loading with coenzyme Q10 by adsorptive precipitation

Seminar Abstract:

Pressurized Gas eXpanded (PGX) liquid technology is a particle formation technique based on the use of carbon dioxide (CO₂) and ethanol as the drying fluid. This technology uses an anti-solvent method to precipitate water-soluble biopolymers from aqueous solution and produces micro or nano-sized particles with unique morphology. Adsorptive precipitation is a method for preparing delivery systems based on the application of supercritical carbon dioxide (SC-CO₂), where a hydrophobic bioactive compound can be loaded on a polymer carrier without the use of any organic solvent during the process. In this thesis research, PGX processing of sodium alginate (SA), and its loading with coenzyme Q10 (CoQ10), a potent antioxidant, by adsorptive precipitation were investigated, in terms of the impact of processing parameters on their physicochemical properties.

For the PGX-processed sodium alginate (PGX-SA), different characterizations such as surface area, morphology, thermal behavior, and viscosity were performed for better understanding of the effect of different processing parameters. PGX-SA had a fibrous structure with a fine network of fibrils, compared to the fine particles with a smooth surface of the unprocessed SA. In addition to the change in the morphology of the particles, the surface area was increased and the bulk density was decreased more than 100 times compared to the unprocessed SA. Use of low concentration (1.0% w/w) of the SA aqueous solution as the feed material, low ethanol flow rate (15 g/min), with the mass flow rate ratio of 4:15:5 of aqueous solution:ethanol:CO₂ resulted in the surface area of 164.5 m²/g of the PGX-SA. The viscosity of the PGX-SA solution was similar to that of the unprocessed SA at the same concentration, which indicated that the molecular weight was not affected by the PGX process.

The CoQ10-loaded PGX-SA (L-SA) obtained by adsorptive precipitation under different processing conditions was investigated for its CoQ10 loading content, morphology, thermal behavior, crystallinity of CoQ10, and dispersion stability in the aqueous system. High circulation power (50 min X 262 mL/min), low operation pressure (200 bar), and the biopolymer with a high surface area (ground PGX-SA) could result in higher loading of the bioactive compound. The highest loading of CoQ10 obtained was 46.9% w/w. Helium ion microscopy images demonstrated a uniform coating of CoQ10 on the surface of PGX-SA. The loaded CoQ10 was still in the crystalline form based on the results from thermal and crystallinity analysis. The zeta potential measurement indicated that the aqueous dispersion of L-SA was a stable system.

The findings provide guidance for further development of the PGX technology, and demonstrated its potential for developing new bioactive delivery systems, especially targeting applications of hydrophobic bioactive compounds such as CoQ10 in aqueous-based products.

Zixiang Liu – MSc with Dr. Feral Temelli