Emulsifying Properties of Ovalbumin in Mixtures with Sulphated Polysaccharides: Effects of Ph, Ionic Strength, Heat and High-Pressure Treatment

The influence of sulphated polysaccharides (dextran sulphate (DS), i-cafiageenan (i-CAR) and kappa-carrageenan (kappa-CAR)) on the emulsifying properties of ovalbumin (OVA) has been investigated over a range of pressures and temperatures. Oil-in-water emulsions (10gl(-1) protein, 200ml(-1) n-tetradecane, pH 6.2) prepared with heat-treated (80 degrees C for 10min) 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 (600MPa for 20min) 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 i- or kappa-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 (>0.04M) led to unstable emulsions, and so the protective effect of DS was lost. High-pressure treatment (600MPa) 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. (C) 2000 Society of Chemical Industry.