Peineng Zhu | 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 PhD Final Exam Seminar by Peineng Zhu. This seminar is open to the general public to attend.

PhD with Dr. Lingyun Chen.

Zoom Link: https://ualberta-ca.zoom.us/j/95163375435?pwd=SO6MTHkocxrLduFsVm4RtaZNfElcpF.1

Meeting ID: 951 6337 5435
Passcode: 165867

Thesis Topic: Study of pea protein gelation mechanism for broader applications as food and biodegradable materials 

Abstract: 

Pea protein is an alternative protein source that has gained considerable attention yet its inferior gelling capacity has limited its applications. The objective of this research was to develop gel-based systems with enhanced and novel properties from pea protein as well as to understand the gel formation mechanisms to expand the potential applications of pea protein as both food and biodegradable materials. In the first study, pH shifting process was utilized as a pretreatment to modulate pea protein unfolding and aggregation, followed by heat-induced gelation. The results revealed that the extension of holding time at pH 12 resulted in the formation of robust three-dimensional (3D) coagulum structure of pea protein that remained intact upon adjusting pH back to neutral. Microstructural observation showed a uniform polymer-like network of the heat-induced pea protein gels, leading to a significant increase in gel mechanical strength, elasticity and water-holding capacity (over 95%), which is comparable to the gels derived from some animal proteins.

In the second study, conditions for developing thermo-reversible pea protein gels were investigated using pea protein isolate extracted through a modified salt precipitation method. The presence of higher content of hydrophilic proteins led to improved solubility of the pea protein, especially at lower pH (pH 2.4 – 4.2), which favored the formation of thermo-reversible molecular interactions. This resulted in transparent pea protein gels exhibiting thermo-reversibility, as confirmed by rheological measurements during repeated heating and cooling cycles between 80 °C and 4 °C. This pea protein gel has provided great opportunities of replacing gelatin in various food formulations as gelling agent to provide clarity and texture.

In the third study, combined with 3D printing technology, the potential of thermo-reversible pea protein gels for generating emulsion gels as printing inks was investigated. Conditions including oil fraction, pH value and protein concentration were confirmed as key factors in modulating rheological properties, and consequently, the printability of prepared emulsion gels. Thermally reversible emulsion gels were obtained with oil volume fractions (ϕ) ranging from 0.2 to 0.65, which displayed strong shear-thinning and thixotropic recovery behavior. 3D printing test has further demonstrated excellent printability of emulsion-filled gel with ϕ 0.4, comparable to high internal phase emulsion (HIPE).

Finally, to further expand the applications of pea protein gelation beyond food sector, a bioadsorbent sponge was developed through the gelation of pea protein using liquid foam templating. The formed hydrogel foam was reinforced by enhancing hydrophobic interactions through soaking in ammonium sulfate (AS) solution to generate compressible sponge. The results showed that the pore structure could be modulated by adjusting the concentration of AS solution, which affected the extent of hydrophobic interactions, resulting in difference in mechanical strength and water adsorption capacity of the sponges. Surface modification using polyethyleneimine (PEI) further increased the surface area and porosity that showed favorable adsorption capacity of Cu(II), Zn(II), and Ni(II) ions. The pea protein sponge also demonstrated great reusability and biodegradability, making it an environmentally friendly and sustainable option for potential environmental and biomedical applications.

This research has advanced methods and expanded the understanding of pea protein gelation mechanisms at molecular levels to improve gel properties, enabling broader applications and increasing the value of plant-based crops. By investigating pea protein gelation at its molecular level, this study provides insights into controlling protein unfolding and aggregation through reinforcement of various molecular interactions, enabling the development of gels with diverse properties. The study of pH-shifting modification was shown to effectively regulate protein unfolding and aggregation process to enhance hydrophobic interactions, resulting in gels with great elasticity. Similarly, the study is the first to report thermally reversible gels from pea protein, achieved through the molecular design of strengthened hydrogen bonds. These findings were strategically applied to modulate gel properties, which was further utilized to regulate rheological properties of emulsion system for 3D printing applications. In addition, the first implementation of pea protein gels to environmental application as bio-adsorbents has provided opportunities to utilize protein from by-product streams, creating value-added solutions and promoting sustainable use of agricultural resources.