Whey protein–pectin soluble complexes for beverage applications

There is a strong interest in the consumption of beverages containing whey proteins due to implications in health outcomes such as increased satiety and metabolic regulation. However, low thermal stability limits the conditions under which whey protein beverages can be formulated. Studies have shown that at a narrow pH range near the protein isoelectric points, whey proteins and polysaccharides self assemble into soluble complexes (SCs) that exhibit unique functionality. This study investigated the formation and thermal stability of SCs under conditions relevant to beverage applications. Complexes were formed at pH 5 using whey protein isolate (WPI; 1–6% w/w) and high-methoxyl pectin (HMP; 0.125–0.75% w/w) and then heat-set at 85 °C for 25 min. Hydrodynamic properties, particle size distribution, ζ–potential, and dispersion viscosity were evaluated before and after heat-setting. Mean particle diameter ranged from 300 to 715 nm for unheated SCs, and 230 nm to 1 μm for heat-set SCs. Heat-setting SCs led to a significant (p < 0.05) reduction in intrinsic viscosity from 93.6 mL/g to 79.5 mL/g, suggesting conformational changes that favor a smaller hydrodynamic size. Dispersions of SCs exhibited decreased apparent viscosity, consistent with the lower intrinsic viscosity and smaller particle size. Heat-set SCs (4% WPI, 0.5% HMP) remained as sub-micron particles (d = 303–829 nm) after pH adjustment (pH 4–7) and thermal processing (142 °C for 6 s), indicating that WPI and HMP can be heat-set into complexes with enhanced colloidal stability in beverage applications.