Interfacial ageing effect on the rheology of a heat-set protein emulsion gel

The effect of ageing of the protein monolayer around the droplets on the rheology of a heat-set whey protein emulsion gel has been investigated at neutral pH. A fine beta-lactoglobulin-stabilized emulsion (30 vol.% oil) was either mixed immediately with whey protein isolate or left for up to few days before mixing and subsequent heat treatment (85 degrees C for 35 min). It was found that the aged protein monolayer at the droplet surface had much weaker chemical affinity for the protein gel matrix and thus had less influence on the elastic modulus of the final gel. Under large-deformation, the normal protein emulsion gel has characteristics of both a particle gel and a biopolymer gel, but the gel made from the aged emulsion behaves more like a particle gel. A highly concentrated emulsion gel (59 vol.% oil) has an enormous storage modulus even though there is little unadsorbed protein present in the continuous aqueous phase. The effect of ageing the adsorbed layer prior to heat-treatment is less significant for the concentrated emulsion. (C) 1999 Elsevier Science Ltd. All rights reserved.