Formation of soluble whey protein aggregates and their stability in beverages

Abstract

The objectives of this work were to 1) determine the role of pH in forming thermally stable whey protein isolate (WPI) soluble aggregates (SA), 2) evaluate the functionality of SA formed under a range of conditions, and 3) evaluate SA stability in a model beverage. Whey protein isolate SA were formed using two sources of WPI at pH 6.5 or 7.5, and thermal stability was tested in the presence of 30–60 mM NaCl or 15–30 mM CaCl2. Soluble aggregates from the two sources of WPI exhibited physicochemical and functional differences over the range of conditions investigated. Soluble aggregates formed at pH 7.5, 7% w/w protein, by heating statically at 90 °C for 10 min exhibited lower turbidity and viscosity, and higher solubility when thermally treated in solutions containing salt for both types of WPI, and were more sensitive to CaCl2. Soluble aggregates and a model beverage containing the SA were prepared at pilot scale and evaluated for shelf stability. Soluble aggregates were formed under continuous flow at pH 6.5, 7% w/w WPI, added at 5% w/w to the beverage, and thermally processed. Over nine weeks of storage at 22.5 °C, the beverage with SA had lower turbidity, aggregate size, and viscosity; and the aggregates had a more negative zeta potential. Results indicate that SA can be used to improve thermal and storage stability in beverages containing salts, and that solution and heating conditions can be optimized for improved thermal stability.