Fibrillization of whey proteins improves foaming capacity and foam stability at low protein concentrations Daniela Oboroceanu a,b , Lizhe Wang a,c,⇑ , Edmond Magner b , Mark A.E. Auty a a Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland b Materials & Surface Science Institute, and Department of Chemical and Environmental Sciences, University of Limerick, Limerick, Ireland c Centre de Recherche Public-Gabriel Lippmann, Environment & Agrobiotechnologies Department, Belvaux, Luxembourg article info Article history: Received 19 April 2013 Received in revised form 7 August 2013 Accepted 8 August 2013 Available online 23 August 2013 Keywords: Whey protein Fibril Microfluidization Foam abstract The foaming properties of fibrillar whey proteins were compared with those of native or denatured whey proteins and also with egg white protein. Whey protein foaming capacity and stability were related to protein concentration, pH, time of whipping, pressure and heating treatments. Foams produced from fibrils showed significant improvement in foaming capacity and stability when compared with non-fibril- lar whey proteins. Dynamic high shear (microfluidization) or moderate shear (Ultra-Turrax mixing) of fibrillar protein dispersions did not significantly affect their subsequent foaming properties. Furthermore, foams prepared with fibrillar whey protein (63% protein) had comparable capacity and stability to that from egg white protein, which is the traditional foaming ingredient in food industry. Results suggest that fibrillized whey proteins are highly effective foaming agents even at relatively low protein concentrations (1–3% w/w). Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Whey protein isolate (WPI) and egg white protein (EWP) are of- ten used as foaming agents in the food industry in the manufacture of meringues, cake, whipped toppings and leavened bakery prod- ucts (Campbell and Mougeot, 1999; Damodaran, 1996, 1997; Davis and Foegeding, 2007; Kuropatwa et al., 2009; Linden and Lorient, 1999; Nicorescu et al., 2009a,b; Vaclavik and Christian, 2008; van der Plancken et al., 2007). Previous studies have shown that WPI or EWP can improve and maintain the quality (texture, volume) of ‘‘foamed’’ food, in partic- ular foaming capacity and stability (Davis and Foegeding, 2004; Doi and Kitabake, 1997; Kuropatwa et al., 2009; Vaclavik and Christian, 2008). The foaming properties of WPI are influenced by protein concentration, pH, high pressure, thermal treatment, foam procedure, by their nature and behavior at interfaces (denatur- ation, protein–protein interactions) and by their interactions with other food ingredients (Bouaouina et al., 2006; Croguennec et al., 2007; Damodaran, 1996, 2005; Ibanoglu and Karatas, 2001; Linden and Lorient, 1999; Pittia et al., 1996; Schmitt et al., 2007; Vaclavik and Christian, 2008; Zhu and Damodaran, 1994). The stability of foams is affected by numerous factors such as the protein adsorption from solution at the liquid/gas interface, the surface rheological properties, diffusion of the gas out and into foam cells, size distributions of the cells, liquid surface tension, external pressure and temperature (Morrison and Ross, 2002). Foams are destabilized by drainage that causes thinning of the interstitial liquid film and by its rupture (Stainsby, 1986; Hamley, 2000). The drainage of the liquid will depend on the physical prop- erties of the liquid, particularly viscosity. As the liquid drains from the foam, the bubbles will coalesce. The coalescence can be stabi- lized by the presence of the proteins at the liquid/air interface that can modify the surface tension of the liquid (Stainsby, 1986; Wilde, 2000; Wilde et al., 2004). Protein denaturation (and the nature of the newly developed protein structure) influence the WPI foaming properties as it can af- fect the surface area, the mechanical resistance, viscosity, elasticity and the ability to retain water of the interfacial film (Leman and Dolgan, 2004; Nicorescu et al., 2009a). A mixture of unheated and heat-induced aggregates of WPI can enhance foam stability (Damodaran, 2005; Zhu and Damodaran, 1994). Heating of 5% (w/w) WPI at 70 °C for 1 min improved foam capacity when compared with unheated whey protein (Zhu and Damodaran, 1994), but excessive heating times led to the formation of aggre- gates that can alter the properties of the foam (Bals and Kulozik, 2003; Cayot and Lorient, 1997; Damodaran, 1996, 2005; Davis and Foegeding, 2004; Green et al., 1999; Nicorescu et al., 2009a,b; Zhu and Damodaran, 1994). The foaming properties of WPI were improved by the presence of an optimal aggregate quantity (10% w/w) at the interface (Nicorescu et al., 2009a). However, increasing the percentage of aggregates to >50% (w/w) led to large 0260-8774/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfoodeng.2013.08.023 ⇑ Corresponding author at: Centre de Recherche Public-Gabriel Lippmann, Environment & Agrobiotechnologies Department, Belvaux, Luxembourg. Tel.: +352 470261481; fax: +352 470264. E-mail address: lizhe.wangrau@gmail.com (L. Wang). Journal of Food Engineering 121 (2014) 102–111 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng