Impact of the character of the associative interactions between chitosan and whey protein isolate on the structure, thermodynamic parameters, and functionality of their complexes with essential lipids

Abstract The aim of this work is the clarification of the impact of the character of associative interactions (covalent and non-covalent (electrostatic)) between chitosan (CHI) and whey protein isolate (WPI) on the structure, thermodynamic parameters and functionality of their complexes with essential lipids. These lipids included soybean phosphatidylcholine liposomes (PC), originally rich in omega-6 linoleic fatty acid (LA), enriched in omega-3 α-linolenic fatty acid (ALA) to an equimass ratio with LA. Differential scanning calorimetry and laser light scattering indicated that the covalent (WPI–CHI) conjugate had a greater degree of protein unfolding, a more open architecture of a random coil and a lower density compared to the same parameters of the electrostatic (WPI–CHI) complex. These structural features of the covalent conjugate contributed to the formation of the ternary (WPI–CHI) + (PC−ALA) complex particles with a higher molar mass and density as well as a more open architecture compared with the same parameters of the ternary electrostatic group. Similar properties of these ternary complexes are the following: a nanoscale size; a high aqueous solubility in the vicinity of the WPI isoelectric point (at pH = 5.1); ζ-potential ≥ +30 mV; an increase in the microviscosity of the encapsulated (PC−ALA) liposome bilayers as a result of complexation (data of electron paramagnetic resonance spectroscopy); 40% protection of the liposomes from oxidation under the twofold excess of the biopolymers relative to the lipids in the ternary complexes.