Thermoplastic starch active films enriched with cationic polylimonene: effects of pulsed light treatment on antioxidant properties

Thermoplastic starch (TPS) is a renewable, abundant, and low-cost biopolymer with film-forming capacity, extensively explored as a sustainable alternative to conventional plastics for food packaging applications. This work evaluated the effect of incorporating 5% cationic polylimonene (PLM), a terpenic biopolymer produced from limonene recovered from citrus by-products, into glycerol-plasticized TPS films, combined with pulsed light treatment (6 and 12 J/cm², TPS-PLT6 and TPS-PLT12, respectively), aiming to develop active packaging materials with antioxidant functionality. Films were produced using thermomechanical mixing followed by compression molding. Fourier transform infrared spectroscopy confirmed the incorporation of PLM into the starch matrix. Antioxidant activity was assessed by DPPH and ABTS radical scavenging assays. In the DPPH assay, films without PLM (TPS, TPS-PLT6, and TPS-PLT12) showed no detectable antioxidant activity, whereas PLM-containing films (TPS-PLM, TPS-PLM-PLT6, and TPS-PLM-PLT12) exhibited inhibition values ranging from 4.3% and 5.3%, significantly higher than the control groups (Tukey, p < 0.05). These results indicate that PLM incorporation was the main factor responsible for antioxidant activity, regardless of pulsed light treatment. In the ABTS assay, untreated TPS films showed activity of 13.7%, while pulsed light treatment reduced the antioxidant activity of films without PLM (TPS-PLT6 and TPS-PLT12). In contrast, pulsed light significantly enhanced the antioxidant performance of PLM-containing films, with TPS-PLM-PLT12 reaching the highest value (19.7%), significantly different from all other formulations (Tukey, p < 0.05). Overall, the combination of cationic polylimonene and pulsed light improved the antioxidant properties of TPS films, highlighting the potential of these materials as bio-based active packaging for oxidation-sensitive foods.