Biopolymers and emulsifiers at the air-water interface.: Implications in food colloid formulations

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 (monopahnitin, 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. (C) 2004 Elsevier Ltd. All rights reserved.