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 monom
odal and showed no change with protein concentration. In contrast, a bimoda
l size distribution was obtained for calcium caseinate emulsions at low-cas
einate concentrations, indicating flocculation of oil droplets. In sodium c
aseinate emulsions, the surface protein load increased as caseinate concent
ration 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 ca
seinate emulsion increased gradually with caseinate concentration in the aq
ueous phase. In general, surface protein loads were higher in calcium casei
nate emulsions than in sodium caseinate emulsions. In sodium caseinate emul
sions, beta-casein was adsorbed preferentially at caseinate concentrations
below 1% but no distinct preference of any caseins was observed at higher c
oncentrations. By contrast, in calcium caseinate emulsions alpha(s)-caseins
appeared to be adsorbed preferentially at all caseinate concentrations use
d. These results are discussed in relation to the adsorption behaviour obse
rved in emulsion systems. (C) 1999 Elsevier Science Ltd. All rights reserve
d.