Structural and Morphological Characterisation of Succinic Acid-Crosslinked Sesame Seed Protein Isolate Bioplastic Films

The development of protein-based bioplastics from renewable resources is an important strategy for reducing dependence on petroleum-derived plastics. This study investigated the structural and morphological characteristics of sesame seed protein isolate (SSPI) films modified with succinic acid (SA). SSPI was obtained from defatted sesame protein concentrate by alkaline solubilisation followed by isoelectric precipitation. Film formulations contained 0, 4 and 5% SA on a protein basis, with 30% glycerol reported as plasticiser, and were compression-moulded at 130°C under 3 MPa for 10 min. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to evaluate formulation-dependent changes. The 4% SA film exhibited reported FTIR bands at 840, 922, 1032, 1151, 1235, 1541, 1601, 2930, 3257 and 3668 cm⁻ 1 , whereas the 5% SA film showed bands at 923, 1030, 1234, 1401, 1541, 1624, 2925 and 3264 cm⁻ 1 . SEM observations indicated that the native film was comparatively rough and porous, while the 4% and 5% SA films displayed progressively more compact and homogeneous morphologies. XRD analysis showed substantially narrower reflections for the 5% SA film than for the 4% film, indicating greater diffraction coherence under the reported measurement conditions. The combined FTIR, SEM and XRD findings demonstrate that succinic-acid treatment altered the molecular environment, morphology and diffraction behaviour of the SSPI matrix. The results support the potential of succinic-acid modification as a route for tailoring sesame-protein-based bioplastic structure, while further mechanical, barrier, thermal, water-sensitivity and biodegradation measurements are required to establish application performance.