Phospholipids at the interface: current trends and challenges

Abstract

Phospholipids are one of the major structural elements of biological membranes. Due to their amphiphilic character, they can adopt various molecular assemblies when dispersed in water, such as bilayer vesicles or micelles, which give them unique interfacial properties and render them very attractive in terms of foam or emulsion stabilization. This article aims at reviewing the properties of phospholipids at the air/water and oil/water interfaces, as well as the recent advances in using these natural components as stabilizers, alone or in combination with other compounds such as proteins. A discussion regarding the challenges and opportunities offered by phospholipids-stabilized structure concludes the review.

Figure 1

Representation of phospholipid surface pressure (π) vs. area per molecule (A) isotherm. Grey areas represent the coexistence regions (LC-LE and LE-G). S: solid-like structure region; LC: liquid-condensed region; LE: liquid-expanded region; G: gaseous region. π_S and A_S are the transition pressure and area, respectively, between liquid-like and solid-like structures. π_C and A_C are the critical pressure and area, respectively, between LE and LC/LE coexistence regions (Adapted from Möhwald [11]).

Figure 2

Hysteresis in π–A isotherms for DPPC monolayers at the air–water interface after continuous compression–expansion cycles at pH 7. The arrows indicate the equilibrium spreading pressure (π_e) and the transitions that take place in the monolayer during a compression–expansion cycle between LE, LC and solid phases. Reproduced with permission from Rodríguez Niño et al. [26], Copyright (2008) Elsevier.

Figure 3

(1) Photographs showing a minor part of an aqueous solution at the bottom and a nonaqueous solution above. (A–C) Formation of an organogel diffusing from the interface through the oil phase; photographs were taken after 3.0, 3.5, and 3.8 min, respectively (the bar indicates 1 mm); (2) Schematic representation of the phase and pseudophase transitions in a 1% w/v lecithin solution after addition of water. Adapted with permission from Shchipunov and Schmiedel [68], Copyright (1996) American Chemical Society.

Figure 4

Visualization of the visco-elastic properties of lecithin at the oil/water interface. The system includes a silica particles-in-water dispersion (1%) and a solution of lecithin in sunflower oil (0.1%). From pictures (a) to (c), the needle is pushing down into the water droplet; on picture (d) the needle is pulling up out of the water droplet (the bar represents 2 mm). Reprinted with permission from Pichot et al. [44], Copyright (2012) Elsevier.

Figure 5

Schematic presentation of mayonnaise making process. Catastrophic inversion lines (—) at direct emulsification; and at dynamic emulsification (- - -) when oil is added and (…) when water is added. Reproduced with permission from Thakur et al. [86], Copyright (2008) Colloids and Surfaces A: Physicochemical and Engineering Aspects.

Figure 6

Influence of bile extract (B.E.) and lipase on (1) the mean particle diameter (d_4,3) of 3 wt% corn oil-in-water emulsions (0.6 wt% sodium caseinate, WPI, Tween 20 and lecithin), and (2) the microstructure of 0.6% lecithin-stabilized emulsion (5 mM phosphate buffer, pH 7.0). Adapted with permission from Mun et al. [109], Copyright (2007) Elsevier.

Figure 7

Schematic representation of the preparation of phospholipid vesicles using double emulsion (left) and fluorescent optical micrograph (right) of latex microspheres (green) encapsulated inside DPPC vesicles (red). Reprinted with permission from Shum et al. [120], Copyright (2008) American Chemical Society.