Obtention and Characterisation of Gelatine-Based Hydrogels Reinforced with the Amino Acids Cysteine (Cy) and Glutamine (Gt).

The use of conventional plastics represents a major environmental concern, as approximately 79% ultimately accumulate in landfills or natural ecosystems. Consequently, there is growing interest in the development and application of renewable materials for food packaging. Therefore, the aim of this study was to develop and characterise gelatine-based hydrogels through the incorporation of two amino acids, cysteine and glutamine, thereby contributing to the advancement of safe and environmentally responsible materials. The hydrogels were prepared using the casting method and characterised in terms of their physical and structural properties. The results indicated that the addition of cysteine and glutamine significantly modified the structural, optical, thermal and barrier properties of the gelatine films and hydrogels. Cysteine produced materials with increased opacity, brownish hues and a more hydrophobic surface, changes attributed to the formation of disulphide bonds and the redistribution of non-polar functional groups towards the surface. In contrast, glutamine yielded more transparent and homogeneous films with a more intact internal structure, owing to the development of a more effectively cross-linked and stable polymeric network. Structural (XRD, FTIR) and thermal (TGA, DSC) analyses confirmed that glutamine enhances thermal stability and molecular cohesion, whereas cysteine increases the more ordered structure and rigidity of the matrix. The selection of an appropriate amino acid thus enables the tailoring of functional properties in these biopolymers, representing an effective strategy for their adaptation to biodegradable packaging applications.