Phase behaviour of macromolecular components in biological and food systems.

Reasons for the greatly different phase behaviour of: (i) biological systems (cytoplasm of the cell), (ii) food systems and (iii) beverages are considered. The two phenomena: molecular mimicry and molecular symbiosis presumably control thermodynamic compatibility of biological macromolecules. The three interacting factors underlying molecular mimicry, are: (i) low excluded volume of densely packed protein globules, (ii) chemical resemblance of surfaces of the globules and (iii) the chemical information hidden in the hydrophobic interior of the globules. The symbiotic relationship presumably exists between rod-like macromolecules and protein globules, i.e. between macromolecules of the two extreme conformations typical of biopolymers. For instance, thermodynamic activity of an enzyme can be controlled by dissociation-association of rod-like macromolecules. Due to excluded volume effects, biopolymers behave as if they were in a solution of a higher concentration. Both molecular mimicry and molecular symbiosis could also be of importance for non-specific immune defence, digestion of proteins and formation of food structures. Unlike biological systems, thermodynamic incompatibility is typical of foods and still more of beverages. Denaturation, aggregation and complexing of food macromolecules decrease their mimicry and co-solubility. Due to their relatively low viscosity and high chemical and physical heterogeneity of macromolecules, the phase behaviour of beverages is similar to that of mixed solutions of synthetic polymers. Phase separation of biopolymer mixtures is of importance for controlling composition-property relationship in formulated food and drinks.