Surface-enriched natural hydrophobic deep eutectic solvent in pullulan-cellulose nanocrystal films via immersion-hot pressing: Enhanced barrier and bioactive properties for rice noodle preservation

To address the limitations of high moisture sensitivity and lack of bioactivity in polysaccharide-based packaging, pullulan-cellulose nanocrystal (CNC) composite films were functionalized with a thymol-decanoic acid based hydrophobic deep eutectic solvent (TD-HDES). Two distinct fabrication strategies, mixing-hot pressing (MHP) and immersion-hot pressing (IHP), were developed and compared. At equivalent TD-HDES loadings, IHP-prepared films exhibited significantly superior water vapor barrier properties, surface hydrophobicity, and antioxidant and antibacterial properties compared to their MHP counterparts. Infrared spectroscopy and scanning electron microscopy revealed a surface accumulation of TD-HDES in IHP films, forming a distinct HDES-enriched surface layer driven by pressure- and temperature-induced migration. While TD-HDES incorporation reduced thermal stability without altering the crystalline structure of the pullulan-CNC matrix, the MHP method yielded higher mechanical strength and toughness due to better bulk integration. A shelf-life study demonstrated that IHP-fabricated films effectively preserved fresh rice noodles. After 4 days at 4°C, samples exhibited lower total plate counts, inhibited hardness and chewiness, and reduced cooking loss compared to polyethylene or pure pullulan-CNC films. This study highlights the potential of IHP-induced surface engineering for developing high-performance bioactive packaging for starch-based foods.