In this paper we are concerned with adsorption, structure, topography, and dynamic properties (relaxation phenomena and surface dilatational rheology) of food dairy proteins (beta-casein, caseinate, and whey protein isolate, WPI), water-insoluble lipids (monopalmitin, monoolein, and monolaurin) and phospholipids (dipalmitoyl-phosphatidyl-choline, DPPC, and dioleoyl-phosphatidyl-choline, DOPC) at the air-water interface. Combined surface chemistry (surface film balance and static and dynamic tensiometry) and microscopy (Brewster angle microscopy, BAM) techniques have been used to determine the static and dynamic characteristics of these emulsifiers and their mixtures at the air-water interface. The derived information shows that biopolymer (proteins) and low-molecular-weight-emulsifier (LMWE, monoglycerides and phospholipids) type and their mixtures affect the interfacial characteristics of adsorbed and spread films. Important functional differences have been established between proteins, lipids and phospholipids. The static and dynamic characteristics of mixed films depend on the interfacial composition and the surface pressure (pi). At higher surface pressures, collapsed protein residues may be displaced from the interface by LMWE molecules with important repercussions on the interfacial characteristics of the mixed films.

We designed Air-in-Oil-in-Water (A/O/W) emulsions. First, Air-in-Oil foams were fabricated by whipping anhydrous milk fat. The maximum overrun was obtained at 20 °C. The foams contained 30–35 vol% air and were stabilized solely by fat crystals. To refine the bubble size, foams were further sheared in a Couette’s cell. The average bubble size reached a value as small as 6.5 μm at a shear rate of 5250 s−1. The nonaqueous foams were then dispersed in a viscous aqueous phase containing sodium caseinate to obtain A/O/W emulsions. The shear rate was varied from 1000 to 7500 s−1, allowing to obtain Air-in-Oil globules whose average diameter ranged from 15 to 60 μm. To avoid globule creaming, the aqueous phase was gelled by incorporating hydroxyethyl cellulose. Homogeneous emulsions were obtained with fat globules containing around 22 vol% of residual air. The systems were kinetically stable for at least 3 weeks at 4 °C.