The Stability And Physical Properties Of Egg White And Whey Protein Foams

Food Hydrocolloids 25 (2011) 1687e1701

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Food Hydrocolloids
journal homepage: www.elsevier.com/locate/foodhyd

The stability and physical properties of egg white and whey protein foams explained based on microstructure and interfacial properties
Xin Yang 1, E. Allen Foegeding*
Department of Food, Bioprocessing and Nutrition Sciences, NorthCarolina State University, Box 7624, Raleigh, NC 27695-7624, USA

a r t i c l e i n f o
Article history: Received 22 October 2010 Accepted 9 March 2011 Keywords: Foam Confocal microscopic images Whey Sucrose Mathematic model

a b s t r a c t
The goal of this investigation was to determine if physical models, based on micro-scale (bubbles) and nano-scale (interface) properties, can be used toexplain the macroscopic foaming properties of egg white protein (EWP) and whey protein isolate (WPI). Foam properties were altered by adding different amounts of sucrose (4.27e63.6 g/100 mL) and microstructures were observed using confocal laser scanning microscopy and bubbles were quantitatively measured using image analysis. Addition of sucrose decreased the initial bubble size, corresponding tohigher foam stability and lower air phase fraction. EWP foams were composed of smaller bubbles and lower air phase fractions than WPI foams. Increased sucrose concentration caused a decreased liquid drainage rate due to a higher continuous phase viscosity and smaller bubble sizes. WPI foams had faster rates for liquid drainage and bubble coarsening than EWP foams. The differences were attributed tofaster bubble disproportionation in WPI foams, caused by lower interfacial elasticity and lower liquid phase fractions. The experimentally fitted parameters for foam yield stress did not follow universal trends and were protein type dependent. EWP foams had higher yield stress than WPI foams due to smaller bubble sizes and higher interfacial elasticity. The yield stress of WPI foams increasedslightly with addition of sucrose and cannot be accounted for based solely on model parameters. It appears that changes in stability of EWP and WPI foams can be explained based on physical models while unaccounted for protein-specific effects remain regarding foam yield stress. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Foams have important applications in a variety of food products. Inthe food industry and culinary arts, egg white protein (EWP) has been traditionally used as a foaming agent because of its apparently unique foaming characteristics. Whey proteins have a comparable foaming capacity (overrun or air phase fraction) and a potential to replace EWP as a foaming agent (Peter & Bell, 1930; Richert, 1979). However, lack of foam stability was found to be the major problemassociated with whey proteins (DeVilbiss, Holsinger, Posati, & Pallansch, 1974; Pernell, Foegeding, Luck, & Davis, 2002). In addition, a lower yield stress value was also observed for whey protein isolate (WPI) foams compared to EWP (Davis & Foegeding, 2007). We previously investigated foams made from mixtures of EWP and WPI. Foams made from mixed protein solutions are more

* Correspondingauthor. Tel.: þ1 919 513 2244; fax: þ1 919 515 7124. E-mail address: allen_foegeding@ncsu.edu (E.A. Foegeding). 1 Present address: National Starch Food Innovation, 10 Finderne Avenue, Bridgewater, NJ 08807, USA. 0268-005X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2011.03.008

similar to WPI, showing lower stability and yield stress than EWP (Yang, Berry, &Foegeding, 2009). The difference between the two protein foams becomes more obvious when sugar is added. Sugar is frequently used in aerated food products. The enhancing effect of sugar on foam stability has been mainly attributed to an increase of liquid viscosity (Pugh, 1996); however, when comparing between EWP and WPI foams, a combined effect of solution viscosity and interfacial rheology is...