Structural and thermodynamic properties underlying the novel functionality of sodium caseinate as delivery nanovehicle for biologically active lipids

Using a combination of static and dynamic multiangle laser light scattering, various structural (the weight-average molar weight, Mw; the radius of gyration, RG; the hydrodynamic radius, Rh; the structure-sensitive parameter, ρ = RG/Rh; the density, d), and thermodynamic (the second virial coefficient, A2, reflecting the nature and intensity of both the biopolymer–biopolymer and biopolymer–solvent pair interactions) parameters have been determined for the complex particles formed between sodium caseinate (SCN) and polyunsaturated soy phosphatydilcholine (PC) liposomes in an aqueous medium at the different experimental conditions (pH: 7.0, 6.0, 5.5, and the ionic strength of the buffers: 0.001M, 0.01M, 0.1M). It was established that both the sufficiently high density (>2 mg ml−1) and the specific architecture of the complex particles were the key structural properties providing the novel functionality of SCN particles as delivery vehicles for the polyunsaturated PC, in particular, as the protectors for PC against oxidation, and as the regulators of the initial velocity of the proteolysis of the complex particles under the enzymatic action in-vitro. In turn the thermodynamic affinity of the complex particles for an aqueous medium was found to be the prevailing factor in the control of such characteristic traditional functionality of SCN as the foaming ability. The data of the differential scanning calorimetry testified the maintenance of the bilayers of the phospholipid (dipalmitoylphosphatydilcholine (DPPC)) liposomes under the formation of the complex particles with the protein. Moreover, as a result of the protein–phospholipid interactions the bilayers became even more thermodynamically stable.