Adsorption behaviour of sodium and calcium caseinates in oil-in-water emulsions

Adsorption behaviour of commercial sodium and calcium caseinates at the oil droplet surface in 30% (w/w) soya oil-in-water emulsions has been studied. The concentration of caseinate in the aqueous phase was varied from 0.5 to 5.0% (w/w). Size distribution of sodium caseinate emulsions appeared monomodal and showed no change with protein concentration. In contrast, a bimodal size distribution was obtained for calcium caseinate emulsions at low-caseinate concentrations, indicating flocculation of oil droplets. In sodium caseinate emulsions, the surface protein load increased as caseinate concentration in the aqueous phase was increased from 0.5 to 4.0%, but it levelled off at higher concentrations. However, surface protein loads in calcium caseinate emulsion increased gradually with caseinate concentration in the aqueous phase. In general, surface protein loads were higher in calcium caseinate emulsions than in sodium caseinate emulsions. In sodium caseinate emulsions, beta-casein was adsorbed preferentially at caseinate concentrations below 1% but no distinct preference of any caseins was observed at higher concentrations. By contrast, in calcium caseinate emulsions alpha(s)-caseins appeared to be adsorbed preferentially at all caseinate concentrations used. These results are discussed in relation to the adsorption behaviour observed in emulsion systems. (C) 1999 Elsevier Science Ltd. All rights reserved.