Interactions biopolymer-surfactant

Biopolymer-surfactant and/or biopolymer-biopolymer attraction in adsorption layers due to opposite electrical charges of the interacting molecules... 

Let us consider the various possible types of biopolymer-surfactant interactions. We first note that, because of the amphiphilic nature of both biopolymers and surfactants, it can be envisaged that the mechanistic interpretation could be based on attractive or repulsive interactions acting between the original biopolymer and surfactant molecules/particles or between biopolymer particles modified by the surfactants. For example, attractive interactions could arise from ... 

The situation is complicated by the fact that the cmc value determined in the pure surfactant solution generally differs from that fomid in the presence of biopolymer. This is mainly because the surfactant-biopolymer interactions can shift the equilibrium between free surfactant molecules and their micelles, leading to a change in the effective cmc of surfactant molecules in the biopolymer system (Kelley and McClements, 2003 McClements, 2000 Thongngam and McClements, 2005). 

Semenova, M.G., Il in, M.M., Belyakova, L.E., Antipova, A.S. (2003). Protein + small-molecule surfactant mixtures thermodynamics of interactions and functionality. In Dickinson, E., van Vliet, T. (Eds). Food Colloids, Biopolymers and Materials, Cambridge, UK Royal Society of Chemistry, pp. 377-387. 

It is important to understand the characteristic interactions involved at an interface containing each of the main types of surface-active molecules, i.e., biopolymers (proteins, polysaccharides) and low-molecular-weight surfactants (lipids). But that is not the whole story. In real food systems there are almost always mixed ingredients at the interface. So it is necessary to understand what sorts of mixed interfacial structures are formed, and how they are influenced by the intermolecular interactions. 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

Increased depletion attraction. The presence of nonadsorbing colloidal particles, such as biopolymers or surfactant micelles, in the continuous phase of an emulsion causes an increase in the attractive force between the droplets due to an osmotic effect associated with the exclusion of colloidal particles from a narrow region surrounding each droplet. This attractive force increases as the concentration of colloidal particles increases, until eventually, it may become large enough to overcome the repulsive interactions between the droplets and cause them to flocculate (68-72). This type of droplet aggregation is usually referred to as depletion flocculation (17, 18). 

These interactions are frequently ionic in character. The coulombic forces of interaction between macroions and lower molecular weight ionic species are central to the life processes of the cell. For example, intermolecular interactions of nucleic acids with proteins and small ions, of proteins with anionic lipids and surfactants and with the ionic substrates of enzyme catalyzed reactions, and of ionic polysaccharides with a variety of inorganic cations are all improtant natural processes. Intramolecular coulombic interactions are also important for determining the shape and stability of biopolymer structures, the biological function of which frequently depends intimately on the conformational features of the molecule. 

Bonnaud, M., J. Weiss, and D. J. McClements (2010). Interaction of a food-grade cationic surfactant (lauric arginate) with food-grade biopolymers (pectin, carrageenan, xanthan, alginate, dextran, and chitosan). Journal of Agricultural and Food Chemistry 58(17) 9110-9111. 

Applications for SMSLS include monitoring the instability (or instability) of polymer solutions, such as therapeutic proteins, biopolymers, polymers in specific solvent, temperature, and other variable conditions, floccu-lants, interactions of polymers with surfactants, ions, small molecules, stimuli such as heat or light, etc. Modes of instability can include microgelation, microcrystallization, phase separation, conformational changes, specific associations, dissolution, and degradation. Examples include the... 

Force fields to describe the interactions between organic molecules and inorganic components such as clay minerals have heretofore been associated with substantial uncertainties. In this section, we will describe necessary strategies to derive compatible force fields for reliable simulations of surfactants, biopolymers, and synthetic polymers in contact with oiddic minerals and explain characteristic properties of clay-organic interfaces relevant to exfoliation in nanocomposites. 

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