Neutral Salt Effects on Stability of Whey Protein Isolate Foams

Addition of 0.1 M Na₂SO₄, NaCl, or NaSCN reduced maximum overruns of whey protein isolate (WPI) by 33%, 27%, and 38%. This was attributable to an ionic effect, i.e., the ions interacted with countercharges on the proteins thereby reducing electrostatic interactions. In contrast, at high concentrations (1M), Na₂SO₄ improved foam stability by 76% compared to WPI without salt. Chloride had an intermediate effect, whereas NaSCN did not improve foam stability. Increasing Na₂SO₄ concentration (2M) improved foam stability by 127% compared to control. The relative effectiveness of salts at improving foam stability and heat stability followed the Hofmeister series (SO₄^2-??).