Biopolymer mixtures

Fiebrig I, Davis SS, Harding SE (1995) In Harding SE, Hill SE, Mitchell JR (eds) Biopolymer Mixtures. Nottingham University Press, Nottingham, UK, 373... 

Van Puyvelde, P., Antonov, Y.A., Moldenaers, P. (2002). Rheo-optical measurement of the interfacial tension of aqueous biopolymer mixtures. Food Hydrocolloids, 16, 395-402. 

For purposes of illustration in what follows, we consider the cases of various specific biopolymer mixtures demonstrating the roles of different thermodynamic parameters in determining the tendency towards phase separation. The deciding role of a greater positive value of Ay is indicated for mixtures in which there is a small difference in thermodynamic affinities of the two biopolymers for the solvent, AA2 = A - Au. A pair... 

When a biopolymer mixture is either close to phase separation or lies in the composition space of liquid-liquid coexistence (see Figure 7.6a), the effect of thermodynamically unfavourable interactions is to induce biopolymer multilayer formation at the oil-water interface, as observed for the case of legumin + dextran (Dickinson and Semenova, 1992 Tsapkina et al, 1992). Figure 7.6b shows that there are three concentration regions describing the protein adsorption onto the emulsion droplets. The first one (Cprotein< 0.6 wt%) corresponds to incomplete saturation of the protein adsorption layer. The second concentration region (0.6 wt% < 6 proiem < 6 wt%) represents protein monolayer adsorption (T 2 mg m 2). And the third region (Cprotein > 6 wt%) relates to formation of adsorbed protein multilayers on the emulsion droplets. 

Dickinson, E. (1995). Mixed biopolymers at interfaces. In Harding, S.E., Hill, S.E., Mitchell, J.R. (Eds). Biopolymer Mixtures, Leicestershire, UK Nottingham University Press, pp. 349-372. 

The following sections focus on the description of the state and phase transition behavior of starch systems, as schematically illustrated in Figure 8.5, with an emphasis on their molecular organization and their response to various environments (temperature, solvent, other co-solutes, etc.). Selected material properties are also discussed in an effort to demonstrate structure-function relationships of this biopolymer mixture in pure systems and in real food products. 

More detailed discussion of food polymers and their functionality in food is now difficult because of the lack of the information available on thermodynamic properties of biopolymer mixtures. So far, the phase behaviour of many important model systems remains unstudied. This particularly relates to systems containing (i) more than two biopolymers, (ii) mixtures containing denatured proteins, (iii) partially hydrolyzed proteins, (iv) soluble electrostatic protein-polysaccharide complexes and conjugates, (v) enzymes (proteolytic and amylolytic) and their partition coefficient between the phases of protein-polysaccharide mixtures, (vi) phase behaviour of hydrolytic enzyme-exopolysaccharide mixtures, exopolysaccharide-cell wall polysaccharide mixtures and exopolysaccharide-exudative polysaccharide mixtures, (vii) biopolymer solutes in the gel networks of one or several of them, (viii) enzymes in the gel of their substrates, (ix) virus-exopolysaccharide, virus-mucopolysaccharides and virus-exudative gum mixtures, and so on. 

The chapter has considered some specific features of food biopolymer mixtures related to the formation of food structures. We are still near the starting point in the understanding of nonspecific interactions of biopolymers in solutions and dispersions. The conditions of immiscibility and phase equilibrium have been only studied in a quite limited number of biopolymer mixtures (i) gelatin and polysaccharide,... 

The physical/chemical states and the thermal transitions of food materials determine the process conditions, functionality, stability and overall quality, including the texture, of the final food products. Carbohydrates and proteins— two major biopolymers in various food products—can exist in an amorphous metastable state that is sensitive to moisture and temperature changes (Cocero and Kokini 1991 Madeka and Kokini 1994, 1996). The physical states of components in a biopolymer mixture determine the transport properties, such as viscosity, density, mass and thermal dif-fusivity, together with reactivity of the material. 

Most food systems are of a colloidal as well as a polymeric nature. The presence of a nonadsorbing polymer in a skim milk dispersion induces an effective attraction between the casein particles, called depletion interaction, resulting in phase separation at sufficiently high polymer concentration. Tuinier et al. (2003) discussed the influence of colloid-polymer size ratio, polymer concentration regime, size, poly-dispersity and charges in colloid/biopolymer mixtures, demonstrating the challenging complexity of the subject. 

Bhat, S., Tuinier, R., and Schurtenberger, P. (2006). Spinodal decomposition in a food colloid biopolymer mixture evidenee for a linear regime. J. Phys. Condens. Matter. 18, L339-L346. 

Substantial efforts have been made to understand the mechanisms underlying the structure formation of biopolymer mixtures, such as gel formation, aggregation and phase behaviour. We also need a more detailed understanding of how we can build structures to fracture and break down in a predictable way. This is essential in order to design structures with the desired properties. We caimot easily eat a food product if it does not fracture and break. 

Loren, N. (2001). Structure Evolution During Phase Separation and Gelation of Biopolymer Mixtures. Thesis. Chalmers University of Technology, Gothenburg, Sweden. 

Loren, N., Langton, M., and Hermansson, A.M. (2002). Determination of temperature dependent strueture evolution by FFT at late stage spinodal decomposition in bicontinuous biopolymer mixtures. J. Chem. Phys., 116, 10536-10546. 

Multiple emulsions can also be formed by mixing an oil-in-water emulsion with a thermodynamically incompatible biopolymer mixture. Depending on the formulation and conditions of preparation, oil-in-water-in-water or mixed oil in water/water-in-water multiple emulsions may be formed. These have potential for the controlled delivery of a range of bioactives (Kim et al. 2006). 

Owen, A. J. and Jones, R. A. L. 1998. Rheology of simultaneously phase separating and gelling biopolymer mixtures. Macromolecules 31 7336-7339. 

Stokes, J. R., Wolf, B., and Frith, W. J. 2001. Phase-separated biopolymer mixture rheology prediction using a viscoelastic emulsion model. J. Rheol 45 1173-1191. 

Wolf, B., Scirocco, R, Frith, W. J., and Norton, I. T. 2000. Shear-induced anisotropic microstructure in phase-separated biopolymer mixtures. Food Hydrocolloids 14 217-225. 

Hermansson, A.M. and Svegmark, K., Starch—a phase separated biopolymer system, Biopolymer Mixtures, S.E.Harding, S.E.Hill and J.R.Mitchell, eds., Nottingham University Press, Nottingham, pp. 225-246,1995. 

AN2 Antonov, Y. and Friedrich, C., Aqueous phase-separated biopolymer mixture compatibihzed by physical interactions of the constituents, Polym. Bull, 58, 969, 2007. 

These results show that the range of obtainable morphologies can be significantly enhanced by mixing of functional DHBCs. Another lesson that can be learned from this example is that even very simple mixtures of model polymers (here a DHBC and its phosphonated derivative) can result in complex morphologies via a so far unknown mechanism. This gives a taste of how difficult it is to understand the often synergetic actions of the multi-component biopolymer mixtures, which control biomineralization events as a soluble matrix. 

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