  Using a unique home-made cell for four-contact impedance spectroscopy of
conductive liquid samples, we establish the existence of two low frequency
conductivity relaxations in aqueous solutions of gelatin, in both liquid and
gel state. A comparison with diffusion measurements using pulsed field gradient
NMR shows that the faster relaxation process is due to gelatin macromolecule
self-diffusion. This single molecule diffusion is mostly insensitive to the
macroscopic state of the sample, implying that the gelation of gelatin is not a
percolative phenomenon, but is caused by aggregation of triple helices into a
system-spanning fibre network.
