Ma. Rosario Rodríguez Niño

Implications of interfacial characteristics of food foaming agents in foam formulations

The manufacture of food dispersions (emulsions and foams) with specific quality attributes depends on the selection of the most appropriate raw materials and processing conditions. These dispersions being thermodynamically unstable require the use of emulsifiers (proteins, lipids, phospholipids, surfactants etc.). Emulsifiers typically coexist in the interfacial layer with specific functions in the processing and properties of the final product. The optimum use of emulsifiers depends on our knowledge of their interfacial physico-chemical characteristics - such as surface activity, amount adsorbed, structure, thickness, topography, ability to desorb (stability), lateral mobility, interactions between adsorbed molecules, ability to change conformation, interfacial rheological properties, etc. -, the kinetics of film formation and other associated physico-chemical properties at fluid interfaces. These monolayers constitute well defined systems for the analysis of food colloids at the micro- and nano-scale level, with several advantages for fundamental studies. In the present review we are concerned with the analysis of physico-chemical properties of emulsifier films at fluid interfaces in relation to foaming. Information about the above properties would be very helpful in the prediction of optimised formulations for food foams. We concluded that at surface pressures lower than that of monolayer saturation the foaming capacity is low, or even zero. A close relationship was observed between foaming capacity and the rate of diffusion of the foaming agent to the air-water interface. However, the foam stability correlates with the properties of the film at long-term adsorption.

Protein–emulsifier interactions at the air–water interface

Abstract The main interfacial physico-chemical characteristics and the kinetics of the formation of protein and emulsifier mixed films at the air–water interface are reviewed. Recent advances include the development of new molecular resolution and spectroscopic techniques coupled with surface rheological instruments and the incipient development of computer simulation of the displacement of proteins by emulsifiers.

Interfacial characteristics of β-casein spread films at the air–water interface☆

Casein is well known to be a good protein emulsifier and β-casein is the major component of casein and commercial sodium caseinate. This work studies the behaviour of β-casein at the interface. The interfacial characteristics (structure and stability) of β-casein spread films have been examined at the air–water interface in a Langmuir-type film balance, as a function of temperature (5–40°C) and aqueous phase pH (pH 5 and 7). From surface pressure–area isotherms (π–A isotherms) as a function of temperature we can draw a phase diagram. β-Casein spread films present two structures and the collapse phase. That is, there is a critical surface pressure and a surface concentration at which the film properties change significantly. This transition depends on the temperature and the aqueous phase pH. The film structure was observed to be more condensed and β-casein interfacial density was higher at pH 5. β-Casein films were stable at surface pressures lower than equilibrium surface pressure. In fact, no hysteresis was observed in π–A isotherms after continuous compression-expansion cycles or over time. The relative area relaxation at constant surface pressure (10 or 20 mN m−1) and the surface pressure relaxation at constant area near the monolayer collapse, can be fitted by two exponential equations. The characteristic relaxation times in β-casein films can be associated with conformation–organization changes, hydrophilic group hydration and/or surface rheology, as a function of pH.

Protein adsorption and protein-lipid interactions at the air-aqueous solution interface☆

Abstract In this work we studied BSA (bovine serum albumin) adsorption and BSA-monostearin interactions at the air-aqueous solution interface. Both the surface tension-time dependence and equilibrium surface tension were determined using the Wilhelmy plate method. Temperature, protein concentration in the aqueous phase, the concentration of the lipid spread on the interface and the aqueous phase composition (ethanol and sucrose) were the variables studied. The following conclusions were drawn. (a) The rate of BSA adsorption at the interface increases with both BSA concentration in the aqueous phase and temperature. (b) With ethanol in the subphase the existence of an induction period is observed, which could reflect the existence of BSA-solute interactions in the aqueous phase and at the interface. (c) The rate of BSA adsorption increases when sucrose is present in the bulk phase. (d) The spreading of monostearin at the interface on a protein film causes a rapid reduction in surface tension which can be associated with a displacement of protein by the lipid. After the initial period, surface tension increases with time until the equilibrium surface tension — similar to that of the lipid — is reached, indicating that protein is displaced by monostearin at the interface. (e) When the amount of monostearin spread on the interface is increased, BSA-monostearin interactions both at the interface and in the aqueous bulk phase increase as well. (f) Protein-lipid interactions depend on both protein concentration and aqueous phase composition.

Chapter 15:Role of Electrostatic Interactions on Molecular Self-Assembly of Protein + Phospholipid Films at the Air–Water Interface

Many food formulations are emulsions or foams. The constituent droplets or bubbles are microstructural entities stabilized by the formation of an interfacial emulsifier layer around the particles.1 The properties of the interfacial layer are governed by the composition and structure of the adsorbed ...