Emulsifying properties of ovalbumin in mixtures with sulphated polysaccharides: effects of pH, ionic strength, heat and high-pressure treatment

Abstract

The influence of sulphated polysaccharides (dextran sulphate (DS), ι-carrageenan (ι-CAR) and κ-carrageenan (κ-CAR)) on the emulsifying properties of ovalbumin (OVA) has been investigated over a range of pressures and temperatures. Oil-in-water emulsions (10 g l−1 protein, 200 ml l−1 n-tetradecane, pH 6.2) prepared with heat-treated (80 °C for 10 min) mixtures of OVA + DS (1:0.25 by weight) had increased creaming stability but unchanged average droplet size compared to those made with untreated OVA and OVA + DS. Emulsions made with pressure-processed (600 MPa for 20 min) OVA + DS (1:0.25 or 1:0.5 by weight) mixtures had the best emulsifying efficiency and stability. Under similar experimental conditions, replacement of DS with either ι- or κ-CAR gave emulsions with larger droplets and more rapid serum separation, probably owing to depletion flocculation. High-pressure treatment (600 MPa) of the OVA and mixed biopolymer solutions at pH 6.2 in the presence of salt (>0.04 M) led to unstable emulsions, and so the protective effect of DS was lost. High-pressure treatment (600 MPa) of emulsions prepared with native OVA or OVA + DS mixtures induced significant levels of flocculation, as indicated by changes in the average droplet size and creaming behaviour. © 2000 Society of Chemical Industry