Characterization of electrostatic interactions and complex formation of ɣ-poly-glutamic acid (PGA) and ɛ-poly-l-lysine (PLL) in aqueous solutions

In this study, we examined the possibility of using anionic ɣ-poly-glutamic acid (PGA) and cationic ɛ-poly-L-lysine (PLL) to form polyelectrolyte complexes. Initially, the formation and properties of the complexes were characterized using visual observations, UV-visible spectrophotometry, microelectrophoresis (ζ-potential), and isothermal titration calorimetry (ITC). The impact of pH, ionic strength, temperature, and polymer ratio on complex formation was examined. The electrostatic complexes formed had a 1:4 mass ratio of polyanion-to-polycation at saturation (pH 7.4). The surface potential and aggregation stability of the complexes was highly dependent on solution pH (2 to 12), which was attributed to alterations in the electrical characteristics of the two polyelectrolytes. In particular, insoluble complexes were formed under pH conditions where there was a strong electrostatic attraction between the two polyelectrolytes, whereas soluble complexes were formed when there was only a weak attraction. The addition of salt (≥ 20 mM NaCl) promoted aggregation of the complexes, presumably due to screening of the electrostatic interactions between them. Conversely, temperature (25 to 90 oC) did not have a major impact on the stability of the complexes. These results may be useful for the design of effective oral delivery systems for bioactive agents in foods and other products.Graphical abstract
Source: Food Research International - Category: Food Science Source Type: research