Proteins nonionic surfactant interaction

To reduce the strong interactions occurring between protein and surfactant with AOT systems during LLE, anionic [8,32] and nonionic surfactants [30,33,142] and other interfacial additives [88,124,143] have been included. An improvement on the percent extraction of protein has also been reported for several of these cases [29,32,33,124,142,143]. 

In this section several recently published studies on the interaction of nonionic surfactants with a variety of biological systems, including enzymes, bacteria, erythrocytes, leukocytes, membrane proteins, low density lipoproteins and membranes controlling absorption from the gastrointestinal tract, nasal and rectal cavities, will be assessed. This is a selective account, work having been reviewed that throws light on structure-activity relationships and on mechanisms of surfactant action. 

Such intricate interactions suggest possible synergisms that could be investigated. Will small amounts of added SDS strengthen the protein network causing final displacement with a nonionic surfactant to occur at higher surface pressures Such studies are needed to imderstand subtle interplays between the mixtures of surfactants encoimtered in commercial food samples. 

Steric interaction can be observed in foam or emulsion films stabilized with nonionic surfactants or with various polymers, including proteins. The usual nonionic surfactants molecules are anchored... 

The data indicate that penetration of the monolayer occurs when the polyoxyethylene nonionic surfactants are injected into the substrate. Polar portions of surfactant molecules interact with their counterparts on the protein film through permanent dipole attraction and dipole-induced-dipole (van der Waals) interaction, and electrostatic attraction. The nature of this adsorption disrupts hydrogen bonding which partially stabilizes the tertiary protein structure. This makes the macromolecules more amenable to unfolding, and this has been observed with proteins in the presence of ionic surfactants (22) as well. 

Calcium stearoyl-2-lactylate—a recognized bread dough conditioner (24)—is known to complex with certain water-soluble fractions of wheat protein (3), but there is little hard evidence pointing to a direct interaction between it and gluten proteins on the order of that seen between the nonionic surfactants and gliadin. Some evidence (25) suggests that calcium stearoyl-2-lactylate interacts with gluten proteins in the presence of starch. 

The influence of electrolytes divides into two areas, i.e. the influence on nonionic (uncharged) surfactants and that on ionic materials. For nonionic surfactants, the effects are either salting-out or salting-in , in line with observations from the Hoffmeister series of electrolyte effects on protein precipitation. While there has been much discussion over the past 50 years on the molecular mechanism involved, including many words on the structure of water, Ninham and Yaminsky have recently shown in a landmark paper that the phenomena can be explained by dispersion interactions (194). 

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