M. Rosario Rodríguez Niño

Interfacial characteristics of food emulsifiers (proteins and lipids) at the air-water interface

Abstract Factors affecting the interfacial characteristics (structure, stability, interfacial rheology, molecular diffusion, and rate of film formation) of food emulsifiers (polar lipids and proteins) at the air-aqueous phase interface are reviewed. The effect of interfacial and aqueous phase (water, and aqueous solutions of ethanol, glycerol, sugars, electrolytes, and pH) compositions have been analyzed as variables. Many measurement methods—such as tensiometry (Wilhelmy plate and pendant drop methods), and Langmuir- and Wilhelmy-type film balances—have been used in the experiments. The effect of the interfacial, aqueous phase composition, and operational conditions (surface density, surface pressure, and temperature) of food emulsifiers (lipids and proteins) at the air-aqueous phase interface are discussed.

Protein-lipid interactions at the oil-water interface.

Abstract The distribution of proteins and lipids in food emulsions and foams is determined by competitive and cooperative adsorption between the two types of emulsifiers at the fluid–fluid interfaces, and by the nature of protein–lipid interactions, both at the interface and in the bulk phase. The existence of protein–lipid interactions can have a pronounced impact on the surface rheological properties of these systems. Therefore, these results are of practical importance for food emulsion formulation, texture, and stability. In this study, the existence of protein–lipid interactions at the interface was determined by surface dynamic properties (interfacial tension and surface dilational modulus). Systematic experimental data on surface dynamic properties, as a function of time and at long-term adsorption, for protein (whey protein isolate (WPI)), lipids (monoglycerides), and protein–lipid mixed films at the oil–water interface were measured in an automated drop tensiometer. The dynamic behaviour of protein+lipid mixed films depends on the adsorption time, the lipid and the protein/lipid ratio in a rather complicated manner. The protein determined the interfacial characteristics of the mixed film as the protein at WPI⩾10−2% wt/wt saturated the film, no matter what the concentration of the lipid. However, there exists a competitive or cooperative adsorption of the emulsifier (WPI and monoglycerides), as the concentration of protein in the bulk phase is far lower than that for interfacial saturation.

The effect of temperature on food emulsifiers at fluid-fluid interfaces.

Abstract Heat-induced interfacial aggregation of a whey protein isolate (WPI) with a high content of β-lactoglobulin (>92%), previously adsorbed at the oil–water interface, was studied by means of interfacial dynamic characteristics performed in an automatic drop tensiometer. Protein concentration in aqueous bulk phase ranging between 1×10−1 and 1×10−5 % wt/wt was studied as a variable. The experiments were carried out at temperatures ranging from 20–80°C with different thermal regimes. During the heating period, competition exists between the effect of temperature on the film fluidity and the increase in mechanical properties associated with the interfacial gelation process. Interfacial crystallisation of food polar lipids (monopalmitin, monoolein, and monolaurin) previously adsorbed at the oil–water interface, was studied by interfacial dynamic characteristics (interfacial tension and surface dilational properties). The temperature, ranging between 40 and 2°C, and the lipid concentration in aqueous oil phase, ranging between 1×10−2 and 1×10−4 % wt/wt, were studied as variables. Significant changes in interfacial dynamic characteristics associated with interfacial lipid crystallisation were observed as a function of lipid concentration in the bulk phase. Interfacial crystallisation of food polar lipids (monopalmitin, monoolein, and monolaurin) at the air–water interface, was studied by π-A isotherms performed in a Langmuir trough coupled with Brewster angle microscopy (BAM). A condensation in monoglyceride monolayers towards lower molecular area was observed as the temperature decreased. This effect was attributed to lipid crystallisation at lower temperatures. BAM images corroborated the effect of temperature on the monolayer structure, as a function of the monoglyceride type.