Properties of whey and egg white protein foams

Foams made of varying concentrations (2–20% w/v protein) of egg white and whey protein isolate were compared by measuring rheological and microstructural properties. Egg white proteins formed foams with higher yield stress (τ) at lower protein concentrations and less whipping time than whey protein isolate foams. The model of Princen and Kiss [J. Coll. Interf. Sci. 128 (1989) 176] predicts a relationship among τ, surface tension (σ), phase volume (φ), and bubble size (R32). This was supported by τ increasing with φ, and the relationship between τ and φ1/3 becoming more linear as protein concentration increased. However, egg white foams had yield stress values as much as 100 Pa greater than whey protein foams, despite having similar phase volumes, bubble size, and lower surface tensions. The experimentally determined factors, Y(φ), for egg white and whey protein isolate foams were within the range determined by Princen and Kiss [J. Coll. Interf. Sci. 128 (1989) 176] for concentrated emulsions. Egg white foams were different in that the values for Y(φ) increased at lower phase volumes than for whey protein isolate foams or concentrated emulsions. These results suggest that specific proteins contribute to foam τ by some means in addition to altering surface properties.