Coalescence and flocculation in o/w emulsions of native and denatured whey soy proteins in comparison with soy protein isolates

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 (C+ F%) was calculated from mean droplet size (D-43) without and with 1% SDS. C% and C + F% 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') and low oil volume fraction (phi) 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. (C) 2005 Elsevier Ltd. All rights reserved.