All Gelatin Networks:  1. Biodiversity and Physical Chemistry

Gelatin gels are well-known for their ability to form nonpermanent, physical gels at room temperature and for their numerous applications in photographic and food industries. The difficulties in understanding the processes of gelation and the properties of the physical gels is partly due to the nature of the molecules that exhibit this state: these are often biopolymers. Concerning gelatin, a regain of interest appeared recently, in relation with the development of new types of moleculesmammalian gelatins were almost exclusively considered so far in the literature. In this series of two papers we investigated gelatin samples from various origins, mammalian and fish gelatins, with the aim of comparing their properties to the reference samples generally used in photographic and food applications. The samples were characterized by their imino acid composition, which indeed varies according to the biodiversity of the species from which they are extracted. The physical and chemical aspects are mainly reported in this paper, while the companion paper deals with the rheological properties. The influence of the thermal treatments, of the gelatin concentration, of the molecular weight, and of the solvent (aqueous and mixed solvents) was put in evidence and finally blending of samples was achieved. Optical rotation measurements were mainly performed; they allow us to fully characterize the development of the triple helices, which depends on the parameters mentioned before. A systematic comparison of the temperatures of helix formation and melting was undertaken. The results are discussed in the context of the models of helix−coil transitions often used for proteins and polypeptides and sometimes for polysaccharides.