Effect of the production sites and aging on gelatin structure

Gelatin, extracted from the collagen of animal’s skins or bone, is used, amongst other applications, in the pharmaceutical industry to make hard capsules. Dried gelatin contains about 10-12 % water and is a partiallycrystalline polymer being composed of an amorphous phase (coil structure with primary chains) and a crystal phase. The latter consists of triple-helical fragments that are remnants of the triple-helices naturally found in collagen. Dried gelatin, placed under high temperature and high humidity conditions, a step called aging in industry, tends to loose water solubility in time. This is due to intra- and intermolecular crosslinks formation which modify and stabilize the structure. Aging is always applied to gelatin to test the shelf life of hard capsules. A wide range of variable environmental conditions (pH and time, temperature, humidity …) are observed in the production process and the storage of gelatin. Our goal was to understand how aging and the production sites affect the dried gelatin’s internal structure and if structural differences were involved in the dissolution variability. For that purpose, sixty pig skin gelatins from different origins of production with different dissolution characteristics (pass or fail the USP dissolution test) were analysed using Differential Scanning Calorimetry (DSC) as a function of aging. Significant differences in glass transition temperatures, melting temperatures and the enthalpies of melting were observed according to the origin of production of the samples (different factories). The results showed that the amount of crystals and their stability to heating decreased with aging while the amorphous phase increased. Gelatins from different production sites display different amounts of crystals and a differential stability of both amorphous and crystalline phases. After aging, the gelatins which failed the dissolution test showed a higher amount of amorphous phase. On the basis of these results, schemes of the gelatin structure were proposed.