Metastable properties of biopolymer networks affect significantly the diffusion kinetics of bioactive
compounds. That was shown to be the case in high solid samples of protein and polysaccharide supporting a homogeneous distribution of polyunsaturated fatty acids. Thermomechanical behaviour of
these matrices was characterised in relation to their glass transition temperature (Tg). A free volume
theory of diffusion was considered to treat transport phenomena of fatty acids within glassy polymers. It
was found that at T > T
g the effective diffusion coefficient of microconstituent transport would increase in
accordance with the free volume of the polymer matrix. Fitting experimental diffusivity data in glassy
polymers to a free volume based theory generates a two-parameter equation that calculates the extent of
molecular interaction between macromolecule and microconstituent. Gradual substitution of polymer
with small-molecule co-solute, glucose syrup in this case, induces a plasticising effect that profoundly
affects the level of interaction, hence the diffusion of fatty acids in the condensed biomaterial.