Physicochemical properties and formation mechanism of whey protein isolate-sodium alginate complexes: Experimental and computational study

The study explored the interaction mechanism between whey protein isolate and polysaccharide at the molecular level. Firstly, the effect of pH on the formation of whey protein isolate-sodium alginate complex was investigated. The particle size and turbidity were reduced in the presence of sodium alginate over a wide pH range. They were remarkably decreased (by 65% and 68.5%, respectively) at pH 5.0 (near the isoelectric point), which was confirmed by fluorescence microscopy. Raman spectroscopy results showed that the presence of sodium alginate resulted in more compact structure (α-helix content increased by 7.53% at pH 5.0) of whey protein isolate at pH 5.0. Then, the interaction and formation mechanism of the complex at the molecular level were explored by computational approaches. Molecular docking study showed that the amino acid residues of β-lactoglobulin formed a complex with –COOH and –OH of sodium alginate. Molecular dynamics simulation analysis illustrated that the binding energy (−338.17 kJ/mol) of the complex was relatively low at pH 5.0, indicating that β-lactoglobulin and sodium alginate had relatively strong binding capacity and stability. Electrostatic interactions which belong to non-bonding contribution played a major role in the formation of β-lactoglobulin-sodium alginate complex. This study provided theoretical basis for further research on the interactions between protein and polysaccharide, improving the stability of protein in acidic food.