Characterization of interactions between whey protein isolate and hyaluronic acid in aqueous solution: Effects of pH and mixing ratio

Interactions between whey protein isolate (WPI) and hyaluronic acid (HA) were characterized as functions of pH (6.0-1.0) and protein to polysaccharide ratio (R, 1:4-10:1). Intramolecular soluble complexes formed at pHc of 5.6-5.8, followed by intermolecular insoluble complexes formed at pH phi 1 of 4.4-4.6. Complexes at ratios below 4:1 reached maximum optical value at pH 2.4 while samples above 4:1 peaked at pH 3-3.4 then precipitated. WPI/HA coacervates completely dissociated into soluble complex at pH 1.6-1.8 (pH phi 2). WPI/HA mixtures showed shear thinning behavior and elastic property. Whey protein underwent significant alpha-helix structure change when interacting with HA in range of pH phi 1>pH > pH phi 2 and at low R values (1:4 and 1:2). Scanning electronic microscope (SEM) pictures showed pH and mixing ratio dependent microstructural changes corresponding with phase transition. Data may provide helpful information for further application of WPI/HA complexes in medical, food and cosmetic fields.