Die makromolekulare Charakterisierung der Gelatine

Abstract

The present paper is a review of the author’s work in the gelatin field. Beginning with the dilute gelatin solution at a temperature above the helix-coil transition it is shown that the molecular mass distribution could be evaluated by the combined application of preparative gel chromatography and acrylamide gel electrophoresis. It was found that gelatin as it is applied for photographic, pharmaceutical and food manufacturing purposes has a multimodal molecular mass distribution. The scaling functions of the gelatin molecules in their coiled state were determined for the following quantities: the sedimentation coefficient, the intrinsic viscosity, the radius of gyration and the diffusion coefficient. There was shown that below the helix-coil transition temperature the gelatin molecules at least partially reform the conformation of the native collagen molecules and further if the concentration is higher than the critical gel concentration an elastically active network is formed. The elastically active elements of said gel could be identified as fibrills of typically 50 to 200 Å thickness. It was also found that during gelformation only a distinct fraction of the gelatin molecules enters the elastically active phase (the gel phase). In the complementary phase, in the sol phase, there are preferentially enriched the more watersoluble α₂ chains and their hydrolytic breakdown products. This fact could be explained by the melting point depression of polymer crystals. There is namely a relationship between the polymer-solvent interaction parameter, which is a measure of the solubility of the polymer, and the melting point of the polymer, which says that the better soluble molecules show a higher melting point e.g. a slower crystallisation. The fact that the gelation process can be desribed by the same formalism as the crystallisation of polymers was prooved by Mercier [6]. As a conclusion of this results it could be demonstrated that scaling functions, within experimental error, described the gelation kinetics and the solution viscosity of the gelatin-water system. The sorption isotherm, which is also a technologically important relation, especially for the design of the film drying process, could have been also deduced to molecular parameters of the gelatin-water system.