Coalescence and flocculation in o/w emulsions of native and denatured whey soy proteins in comparison with soy protein isolates Gonzalo G. Palazolo a , Delia A. Sorgentini b , Jorge R. Wagner a,b, * a Centro de Investigacio ´n y Desarrollo en Criotecnologı ´a de Alimentos (CIDCA), CONICET, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 47 y 116, 1900 La Plata, Argentina b Departamento de Ciencias Biolo ´gicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 47 y 115, 1900 La Plata, Argentina Abstract Comparison of coalescence and flocculation stability of o/w emulsions prepared with whey soy protein and soy protein isolates, native and denatured (NWSP, NSI; DWSP, DSI, respectively) was performed. Sodium caseinate (SC) was used as emulsifier control. Emulsions, without and with NaCl (500 mM in aqueous phase) were analysed by backscattering during 24 h in quiescent storage. In the absence of salt, the cream phase global destabilization percentage (D%) at 24 h of NWSP emulsions was the highest, whereas in the presence of NaCl not only NWSP but also NSI emulsions were destabilised. Cream phase stability, expressed as coalescence (C%) and coalescence plus flocculation percentages (CCF%) was calculated from mean droplet size (D 43 ) without and with 1% SDS. C% and CCF% had a polynomial correlation with D%, which indicate that this parameter could reflect the particle size increase due to both coalescence and flocculation processes. The higher stability of denatured soy protein (DWSP, DSI) emulsions respect to those prepared with native proteins could be related with the presence of hydrated flocs formed during quiescent storage. In these emulsions, high elastic modulus (G 0 ) and low oil volume fraction (f) values indicated an hydrated and gel-like structure of cream phase. Thermal denatured whey soy proteins, without antitryptic activity, allowed to obtain as coalescence stable emulsions as those prepared with SC. Although backscattering method detected changes in particle size with a less sensibility than droplet size determination, it allowed the continue evaluation of global stability in non-diluted emulsions. q 2005 Elsevier Ltd. All rights reserved. Keywords: Backscattering; Coalescence and flocculation stability; Cream phase; o/w Emulsions; Whey soy proteins 1. Introduction Coalescence stability affects processing or shelf life of oil in water emulsions. Depending of product high or low coalescence stability is desired (Britten & Giroux, 1991). The coalescence probability increases as the fluctuations in the membrane shape may them become large enough to form a hole, which extends from one droplet to another. The magnitude of the shape fluctuations is governed by the interfacial tension, film rheology and mechanical applied forces (Evans & Wennerstrom, 1994; McClements, 1999). The emulsifying properties of isolate soybean proteins, which contains the storage proteins, glycinin and b-conglycinin, have been studied (Kinsella, 1979; Peng, Quass, Dayton, & Allen, 1984). However, whey soy proteins need further research. The main components of this fraction are the Kunitz trypsin inhibitor and lectins with a molecular mass of 20 and 120 kDa, respectively. The antinutritional activity and thermolability of these proteins have been reported in previous works (Liener, 1981). In previous works in our laboratory, structural characteristics and surface behaviour of native and thermal denatured whey and storage soy proteins were studied (Palazolo, Sorgentini, & Wagner, 2004; Sorgentini & Wagner, 1999). The coalescence of o/w emulsions prepared with proteins is a process strongly accelerated in shear stress conditions because it is slow in comparison with creaming and flocculation (Britten & Giroux, 1991). Mitidieri and 0268-005X/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2004.10.022 Food Hydrocolloids 19 (2005) 595–604 www.elsevier.com/locate/foodhyd * Corresponding author. Address: Centro de Investigacio ´n y Desarrollo en Criotecnologı ´a de Alimentos (CIDCA), CONICET, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 47 y 116, 1900 La Plata, Argentina. Tel./fax: C54 221 4254853/4249287/4890741. E-mail address: jrwagner@biol.unlp.edu.ar (J.R. Wagner).