Weight correction for differential scanning calorimetry analysis of archeological keratin fibres

Archaeological fibres can be defined as natural fibres that belong to different time periods and are found at cemeteries or excavation sites. The chemical and physical structure of the fibres changed over time in response to specific burial environments and conditions of preservation. Proteins of ancient fibres show different degrees of degradation due to the environmental conditions. Some have nearly been destroyed and their colour changed due to immersion in different types of media, contamination with soil and by microbial attack. Keratin fibres are able to absorb ions from the environment to a great extend. This kind of mineralization leads to a reduced protein content compared to virgin keratin fibres.Differential Scanning Calorimetry (DSC) in water has been used to study the denaturation behaviour of α-helical material in keratin fibres Intermediate Filaments, IF), the role of the highly cross-linked Intermediate Filament associated Proteins (IFAPs) and the effect of physical and chemical treatments on keratin fibres. Changes in the protein backbone of keratin fibres can be studied by this technique. The value for the denaturation enthalpy ΔH depends on the protein content of the keratin fibres. Standard DSC assumes that the protein content of the analyzed fibres is comparable. However, archaeological fibres shows a reduced protein content which reflects on the value of the denaturation enthalpy ΔH. To get a more reliable value for the state of preservation of the IF proteins of the archaeological fibres a weight correction in response to the reduced protein content has been applied. The pronounced increase in denaturation enthalpy ΔH after weight correction give more authentic information about the damage in the α-helical proteins of keratin fibres.