Spectroscopic insights and comparative kinetic analysis of citral release from thermoplastic starch-PBAT films

Spectroscopic techniques, namely Fourier-transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance (NMR) were employed to elucidate the molecular interactions governing the functionalities of citral embedded in acetylated starch (AS: Cit) and in octenyl succinated starch (OS:Cit). FTIR revealed new absorption peaks at 1712 and 2970 cm^-1, corresponding to aldehyde (-CHO) and methyl (-CH₃) groups of citral, located at C1 and C8-C10 of the molecular structure. These assignments were corroborated by ¹³C NMR resonances at δ 192 and 18-25 ppm, and by ¹H NMR aldehydic protons (H8) at δ 9.8 and 9.9 ppm, attributable to neral and geranial. Proton integration values were consistently higher in OS:Cit than AS:Cit, indicating greater citral incorporation, which correlated with higher loading efficiency in OS:Cit (57.3-59.0%) compared with AS:Cit (52.5-53.2%). Nevertheless, AS:Cit-PBAT films exhibited greater citral release and stronger antimicrobial efficacy against Bacillus cereus within the first 24 h, whereas OS:Cit-PBAT demonstrated delayed release. Release profiles of geranial and neral fitted best with the Weibull model (R² = 0.836-0.993), confirming diffusion-controlled mechanisms. These findings provide mechanistic insights into citral-starch interactions, establish predictive release models, and highlight TPS:Cit-PBAT films as promising active packaging materials for short-shelf-life fresh food preservation.