26The foaming properties of fibrillar whey proteins were compared with those of native or 27 denatured whey proteins and also with egg white protein. Whey protein foaming capacity and 28 stability were related to protein concentration, pH, time of whipping, pressure and heating 29 treatments. Foams produced from fibrils showed significant improvement in foaming capacity 30 and stability when compared with non-fibrillar whey proteins. Dynamic high shear 31 (microfluidization) or moderate shear (Ultra-turrax mixing) of fibrillar protein dispersions did 32 not significantly affect their subsequent foaming properties. Furthermore, foams prepared 33 with fibrillar whey protein (≤ 3% protein) had comparable capacity and stability to that from 34 egg white protein, which is the traditional foaming ingredient in food industry. Results 35 suggest that fibrillized whey proteins are highly effective foaming agents even at relatively 36 low protein concentrations (1-3% w/w).
Introduction 51Whey protein isolate (WPI) and egg white protein (EWP) are often used as foaming agents in 52 the food industry in the manufacture of meringues, cake, whipped toppings and leavened 53 bakery products (Campbell and Mougeot, 1999;Damodaran, 1996Damodaran, , 1997 Davis and 54 Foegeding, 2007; Kuropatwa et al., 2009; Linden and Lorient, 1999; Nicorescu et al., 2009a Nicorescu et al., , 55 2009b Vaclavik and Christian, 2008; van der Plancken et al., 2007). 56Previous studies have shown that WPI or EWP can improve and maintain the quality (texture, 57 volume) of "foamed" food, in particular foaming capacity and stability (Davis and Foegeding, 58 2004; Doi and Kitabake, 1997; Kuropatwa et al., 2009; Vaclavik and Christian, 2008). The 59 foaming properties of WPI are influenced by protein concentration, pH, high pressure, 60 thermal treatment, foam procedure, by their nature and behaviour at interfaces (denaturation, 61 protein-protein interactions) and by their interactions with other food ingredients (Bouaouina 62 et al., 2006;Croguennec et al., 2007;Damodaran, 1996Damodaran, , 2005Ibanoglu and Karatas¸ 2001; 63 Linden and Lorient, 1999; Pittia et al., 1996;Schmitt et al., 2007; Vaclavik and Christian, 64 2008; Zhu and Damodaran, 1994). 65The stability of foams is affected by numerous factors such as the protein adsorption from 66 solution at the liquid/gas interface, the surface rheological properties, diffusion of the gas out 67 and into foam cells, size distributions of the cells, liquid surface tension, external pressure and 68 temperature (Morrison and Ross, 2002). Foams are destabilized by drainage that causes 69 thinning of the interstitial liquid film and by its rupture (Stainsby, 1986; Hamley, 2000). The 70 drainage of the liquid will depend on the physical properties of the liquid, particularly 71 viscosity. As the liquid drains from the foam, the bubbles will coalesce. The coalescence can 72 be stabilized by the presence of the proteins at the liquid/air interface that can modify the 73 surface tensio...