Static and Dynamic Properties of a Whey Protein Isolate and Monoglyceride Mixed Films at the Air−Water Interface

Abstract

Prof. Garcı ´a Gonza ´lez, s/nu ´m. 41012-Seville. SpainThe static and dilatational properties of mixed emulsifiers are of interest due to their importance in relation to dispersion formation and stability. In this work, we have used different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial dilatational rheology), to analyze the static (structure, morphology, reflectivity, and miscibility) and dynamic (surface dilatational properties) characteristics of whey protein isolate (WPI) and monoglyceride (monopalmitin or monoolein) mixed films spread on the air-water interface. The static and dynamic characteristics of the mixed films depend on monolayer composition and the surface pressure. At higher surface pressures, collapsed WPI residues may be displaced from the interface by monoglyceride molecules with important repercussions on the interfacial characteristics of the mixed films. A close relationship between interfacial dilatational rheology and changes in molecular structure, interactions, miscibility, and relaxation phenomena has been established from the frequency dependence of the surface dilatational properties.

Structural and Shear Characteristics of Adsorbed β-Casein and Monoglyceride Mixed Monolayers at the Air/Water Interface

“…At surface pressures higher than that for the β-casein collapse, the π-A isotherm for mixed monolayers was parallel to that of monopalmitin. These data are in good agreement with those deduced for spread β-casein + monopalmitin 20 and β-lactoglobulin-monopalmitin [27][28][29] mixed films. These results suggest that, at π > π c β-casein , a protein displacement by the monoglyceride from the air/water interface occurs.…”

Structural and Topographical Characteristics of Adsorbed WPI and Monoglyceride Mixed Monolayers at the Air−Water Interface

“…Since the surface concentration is actually unknown for the adsorbed monolayer, the values were derived by assuming (Figure B) that the A values for adsorbed and spread monolayers were equal at the collapse point of the mixed film. , This assumption can be supported by the fact that, for protein films, the equilibrium spreading pressure (π e ), the surface pressure at the plateau for a saturated WPI adsorbed film, and the collapse pressure for adsorbed (Figure A) and spread ,, WPI monolayers are practically equal.…”

“…Surface Film Balance . Measurements of surface pressure (π)−area ( A ) isotherms of WPI−monoglyceride mixed films at the air−water interface were performed on a fully automated Wilhelmy-type film balance as described previously. − Before each measurement, the film balance was calibrated at 20 °C. For protein adsorbed films from water a protein solution at 1 × 10 -6 −1 × 10 -5 % (wt/wt) was left in the trough and time allowed for protein adsorption at the interface.…”

Structural, Topographical, and Shear Characteristics of Milk Protein and Monoglyceride Monolayers Spread at the Air−Water Interface

“…The study of such dynamic behavior can be described by interfacial rheology. − Interfacial rheology is important for food colloids (emulsions and foams) because the structural and mechanical properties of food emulsifiers at fluid−fluid interfaces have an influence on the stability and texture of the product. In addition, interfacial rheology is a very sensitive technique to monitor the interfacial structure and concentration of single emulsifiers at the interface or the relative concentration, the competitive adsorption, and the magnitude of interactions between different emulsifiers at the interface. ,− …”