Abstract
A survey of the literature clearly indicates the potential of steric exclusion phenomena between proteins and polysaccharides in enhancing the functional properties of food/non-food products. However, in spite of the range and depth of research over the last fifty years, even the most recent reviewers accept that there are still very significant areas of obscurity in our understanding of how phase-separated proteins and polysaccharides contribute to the texture of industrial products. Recently, some progress has been made in the understanding of how biphasic gels behave in terms of phase continuity, phase inversion and, above all, solvent distribution between the two phases. It is based on the assumption that either bulk phase separation to equilibrium takes place first with gelation then occurring subsequently and independently in each phase or the fastest gelling component does so prior to the establishment of a true thermodynamic equilibrium with subsequent gelation of the second, slower gelling species. A number of theoretical treatments from the realm of synthetic polymers were adapted for use in biopolymer networks, namely: I) the application of blending laws to the phase separated biopolymer gels was attempted, taking into account the complication of solvent presence as a third component which can partition itself between the two polymer constituents, ii) the modulus development as a function of concentration (cascade formalism) was derived from the relationship between equilibrium shear modulus and number of elastically effective network chains considering that gel formation due to non-covalent interactions between biological macromolecules is described by a monomer-dimer equilibrium (link «=» two free sites) and iii) the Flory de-swelling theory was applied to biopolymer gels assuming permanent networks on the basis of stress relaxation and dynamic oscillatory evidence. The conclusions, drawn from the theoretical postulates, were put to the test by acquiring independent evidence about the structural and mechanical properties of mixed gels using mechanical spectroscopy, differential scanning calorimetry, and microscopy. Studies were done using mixtures of several biopolymers (maltodextrins, gelatin, milk and soya proteins) in an attempt to identify a general pattern of behavior in the phase separation of biphasic gels. Overall, the analysis (theoretical model and experimental techniques) was extremely encouraging and the lack of direct (instrumental) determination of phase-composition makes it a most appropriate tool of attack for future research on biopolymer co-gels.
Original language | English |
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Journal | International Journal of Polymer Analysis and Characterization |
Volume | 1 |
Issue number | 2 |
Pages (from-to) | 99-118 |
ISSN | 1023-666X |
DOIs | |
Publication status | Published - 1995 |
Externally published | Yes |