Whey protein-based beverage formulation: Stability diagrams for acidic drinks made with milk whey protein isolate

Whey protein isolates can be obtained from cheese whey or directly from skim milk via microfiltration, producing milk-derived whey protein isolate (mWPI). However, the differences between these protein sources in acidic beverage applications need further studies. Therefore, this study aimed to characterize mWPI functionality by developing stability diagrams in acidic beverage applications. Two lots of mWPI powder were obtained from a commercial manufacturer. A 10% (wt/wt) stock solution was prepared by rehydrating powders at room temperature for 30 min, followed by overnight storage at 4°C to ensure complete hydration. Protein concentrations were adjusted to 2, 4, 6, 8, and 10% (wt/wt). Samples were then adjusted to pH 3.0, 3.5, 4.0, 4.5, and 7.0, followed by the addition of NaCl (0, 5, and 10 mM). Low-pH samples (≤4.5) were heated to 109°C for 3 s, while high-pH samples (>4.5) were heated to 141°C for 6 s, then rapidly cooled. Samples were analyzed for turbidity, particle size, aggregation index (AI), soluble protein content, viscosity, and native PAGE. Beverages transitioned from clear to turbid at pH ≥ 3.5, regardless of salt concentration. Samples at pH 3.0- < 3.5 with protein concentrations of 3-10% exhibited the smallest particle sizes (<150 nm) and remained optically clear. Increased pH and salt concentration promoted protein unfolding, aggregation, and reduced solubility, resulting in higher turbidity and viscosity. In conclusion, mWPI enables formulation of clear, stable acidic beverages at protein concentrations up to ∼8% (wt/wt). These findings provide a practical framework for designing high-protein acidic dairy beverages with improved stability and functionality.