Colloids and Surfaces A: Physicochem. Eng. Aspects 499 (2016) 10–17 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Interfacial properties of highly soluble crayfish protein derivatives Manuel Felix a , Alberto Romero a,∗ , Jan Vermant b,c , Antonio Guerrero a a Departamento de Ingeniería Química, Universidad de Sevilla, 41012 Sevilla, Spain b Department of Chemical Engineering, KU Leuven, University of Leuven, W. de Croylaan 46-3001, Leuven, Belgium c Department of Materials, ETH Zürich, CH-8093 Zürich, Switzerland h i g h l i g h t s • Two highly soluble crayfish protein derivatives are evaluated at pH 2 and 8. • Adsorption kinetics seems to be dom- inated by the diffusion stage. • Dilatational elastic response seems to be dominated by Gibbs elasticity. • Interfacial shear creep response is highly elastic at pH 2 but Newtonian at pH 8. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 30 January 2016 Received in revised form 1 March 2016 Accepted 14 March 2016 Available online 31 March 2016 Keywords: Crayfish protein Dilatational rheology Interfacial tension Interfacial shear rheology Double-wall ring a b s t r a c t An analysis of the interfacial behaviour of two alternative protein derivatives with high solubility has been carried out at two different pH values (2 and 8). The protein derivatives (protein content higher than 50 wt.%) have a globular protein fraction mainly consisting of sarcoplasmic proteins (CFS); and a protein hydrolysate, (CFH), both obtained from crayfish surpluses. The physicochemical characterisation included protein solubility (higher than 80%) and surface charge as well as chemical analysis (elementary, sulfhydryl and disulphide groups). This was complemented with an interfacial characterization included measuring the surface pressure and surface dilatational measurements with a drop tensiometer, and interfacial shear rheology measurements performed using a double-wall-ring geometry. Whereas both types of protein derivative have significant interfacial activity (surface pressure between 20 and 40 mN/m), the difference in their behaviour is small In contrast, a strong influence of pH on the interfacial behaviour has been found for both soluble protein fractions. At pH 2, globular sarcoplasmic pro- tein fraction yields lower surface pressures but highly viscoelastic interfaces, with 2D gel-like behaviour. At pH 8, on the other hand, CF proteins form quite rigid and more brittle interfaces, being resistant to dilatational deformations and showing high sensitivity to shear. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The important role of proteins in both the emulsification pro- cess and emulsion stability has been widely recognised over the last decades. The ability to emulsify is related to the reduction of ∗ Corresponding author at: Departamento de Ingeniería Química, Universidad de Sevilla, Facultad de Química, 41012 Sevilla, Spain. E-mail addresses: alromerogarcia@gmail.com, alromero@us.es (A. Romero). interfacial tension as the protein molecules adsorb to the interface. The lower value of the interfacial tension facilitates the breakup of droplets during emulsion formation [1]. Moreover, proteins are also able to provide full droplet surface coverage [2,3], tending to form thick adsorption layers, in which the protein molecules are often bound together by cohesive bonds, showing little lateral mobil- ity. Among other phenomena, adsorbed protein layers are very effective in stabilizing thin films between emulsion droplets due to the combination of several factors. The occurrence of repulsive http://dx.doi.org/10.1016/j.colsurfa.2016.03.037 0927-7757/© 2016 Elsevier B.V. All rights reserved.