Partial Restriction. Restriction lift date: 2030-09-30
Application of fish gelatin in novel emulsion-based delivery systems
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Date
2024
Authors
Lin, Yichen
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
In recent years, fish gelatins (FG) have emerged as promising substitutes for mammalian gelatin, attracting extensive attention. Owing to their dual characteristics of emulsifying and gelling, gelatins are considered valuable ingredients in emulsion-based delivery systems. However, the application of FG is limited by its inferior functionality. The combination of FG with macromolecules is recognized as an effective strategy to enhance the properties of gelatin-stabilized emulsions or emulsion gels. Whey protein fibrils (WPF) were first introduced into FG-stabilized emulsions to investigate how binary proteins collaborate to stabilize oil-in-water emulsion systems. Compared to whey protein isolate (WPI), WPF displayed increased surface hydrophobicity and interfacial activity at pH 7, leading to enhanced creaming stability of emulsions. When FG was combined with WPI and WPF, it contributed to the formation of a 3D network, thus enhancing the physical stability of emulsions. Additionally, WPI and WPF improved surface activity in binary protein systems. FG-WPF combinations exhibited superior compatibility, a faster gelation rate, enhanced viscoelastic properties, and increased deformation resistance compared to FG-WPI.
Further studies assessed the performance of WPF relative to soy protein isolate fibril systems (SPF) in FG-stabilized emulsion gels, crucial for understanding how protein fibril source and concentration influence emulsion properties. FG was mixed with WPF and SPF under electrostatic interactions, enhancing hydrophobicity and interfacial activity. WPF effectively reduced droplet size and improved viscoelastic properties. In contrast, at lower concentrations (0.1%), SPF was prone to induce coalescence but enhanced viscoelasticity more effectively. Introducing protein fibrils significantly improved the gel strength of FG emulsion gels at low temperatures. However, they remained thermo-reversible gels, which are fragile under temperature changes and external forces.
Nanoemulsions are a critical form of emulsion systems, known for their superior creaming stability and enhanced efficacy in delivering bioactive ingredients. In this study, cold water fish gelatin (CFG) was combined with WPI or WPF under various pH conditions to evaluate their creaming stability. Both CFG-WPI and CFG-WPF binary protein-stabilized nanoemulsions exhibited excellent stability at pH 3, 9, and 11, with CFG-WPF nanoemulsions demonstrating improved physical stability and smaller particle sizes under these conditions. However, at pH 5 and 7, near the proteins’ isoelectric points, the emulsions became unstable. Flocculated oil droplets were the primary cause of extensive aggregation, leading to phase separation after centrifugation at pH 7. Reducing the content of whey proteins (WPI and WPF) improved creaming stability by decreasing the degree of flocculation. However, a low concentration of whey proteins increased the risk of coalescence, particularly in CFG-WPI-stabilized emulsions at neutral pH.
Transglutaminase (TG) could effectively modify FG, improving its emulsifying and thermal stability. When FG was treated with TG, the crosslinked products ranged from gelatin molecules to microgels and their mixtures. The transition of emulsions from conventional to Pickering types was observed as gelatins evolved from molecules to microgels. With increased TG levels, the emulsion droplets became more homogeneous, and protein networks formed around the oil droplets. Emulsions stabilized with TG-modified FG exhibited improved physical stability compared to those stabilized with unmodified FG.
To further investigate the impact of TG crosslinking on the structural and mechanical properties of emulsion gels, FG-stabilized nanoemulsions were prepared via two-step homogenization and embedded in a gelatin gel matrix induced by TG crosslinking. Non-crosslinked FG emulsion gels were thermally reversible and exhibited higher mechanical strength than TG-crosslinked gels at low temperatures. The duration of crosslinking was positively correlated with gel rigidity, resulting in a denser structure more resistant to deformation, particularly at room and physiological temperatures. TG modification significantly enhanced storage stability and delayed the release rate of β-carotene during simulated gastric digestion.
The findings of this study reveal the role of protein interactions and enzymatic crosslinking in the stabilization of gelatin-based emulsions and emulsion gels. This research could provide innovative strategies for designing structured emulsions and emulsion gels with tunable textures and improved stability.
Description
Partial Restriction
Keywords
Fish gelatin , Emulsion , Binary protein , Transglutaminase
Citation
Lin, Y. 2024. Application of fish gelatin in novel emulsion-based delivery systems. PhD Thesis, University College Cork.