Pectin-hemicellulose-nanolignin films with improved UV-barrier, moisture resistance and antioxidant properties

Packaging films and coatings from pectin and hemicelluloses have seen significant growth in the food industry, aided by their other properties such as biodegradability and renewability. However, films or coatings developed from only pectin or hemicellulose have numerous drawbacks in terms of their physicochemical, functional, and mechanical properties. Due to their high hydrophilic nature, such films are highly susceptible to moisture, limiting their application in food packaging. Some strategies that have been employed to improve the mechanical, functional, and barrier properties of pectin and hemicellulose-based films include crosslinking with other polymers or the incorporation of hydrophobic substances such as lipids and lignin. Lignin improves the UV-barrier, mechanical, and antioxidant properties of films; however, it has poor dispersibility in polymer matrix due to its irregular morphology and broad molecular weight distributions. As an alternative, lignin nanoparticles exhibit stable morphology, surface chemistry and particle size distribution alleviating the drawbacks of irregular-shaped lignin. In the study, pectin, hemicellulose, and lignin nanoparticle (LNPs) films were developed and characterized based on the physicochemical, mechanical, optical, moisture barrier and antioxidant properties. Optical properties, chemical structural changes, and hydrophobicity were analyzed using UV-visible spectroscopy (UV-Vis), Fourier Transform infrared spectroscopy (FTIR), and contact angle measurements. A thermogravimetric analyzer was used to study the thermal behavior of films whereas atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to monitor the surface morphology/topography. The mechanical properties of films were assessed using the Instron machine and DPPH free radical assay used for the antioxidant activity. The LNPs were compatible with the hemicellulose-pectin matrix resulting in self-supporting thin films with enhanced tensile strength, water vapor and UV-barrier properties. Moreover, improvement in DPPH radical scavenging activity of pectin/hemicellulose/LNPs films was observed indicating improved antioxidant activity compared to films without LNPs. The results indicate that pectin/hemicellulose/LNPs films could be promising as an active packaging or coating for the preservation of food.