Abstract
Aeration properties of acidified casein-stabilized emulsions containing liquid oil droplets have been compared to the whipping of dairy cream. The foam systems were characterized in terms of overrun, microstructure, drainage stability, and rheology. With acidification using glucono- δ -lactone, the casein-stabilized emulsions could be aerated to give foams of far higher overrun (>600%) than whipped cream (∼120%). The development of foam volume, stability and rheology in the aerated casein-stabilized emulsion systems was found to be strongly dependent on the pH and the concentration of added calcium ions. Whereas whipped cream is stabilized by partially coalesced fat globules, the casein emulsion foams are stabilized by aggregation (gelation) of the protein coat surrounding the oil droplets. Casein emulsion foams formed at low pH were found to be more stable than whipped cream, whilst those formed at high pH were predominantly liquid-like and unstable. Instability arose in the acidified casein emulsion foams mainly through gel syneresis. We conclude that there are substantial textural differences between whipped cream and acidified casein emulsion foams, especially in terms of the small-deformation rheology and the extent of the linear viscoelastic regime.
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