Development and characterization of bioactive citric acid–crosslinked chitosan films functionalized with sorghum extracts

: While chitosan has emerged as a leading biodegradable alternative to petroleum-based plastics, its high moisture sensitivity and limited active functionality often compromise its barrier performance and shelf-life extension capabilities in food-packaging applications. In this study, citric acid-crosslinked chitosan films plasticized with glycerol and functionalized with sorghum glume extracts were developed and characterized. Film thickness remained uniform (0.046-0.056 mm), indicating good casting reproducibility, with reduced water sensitivity, resulting in moderate water solubility (16.8-19.5%), and low water vapour permeability (0.533-0.605 × 10-9 g·m-1·s-1·Pa-1). Increasing glycerol content enhanced film flexibility, with EAB reaching up to 53.47%. Sorghum extracts improved the functional performance of the films, reducing transparency and increasing UV-light shielding while enhancing antioxidant activity. The highest antioxidant performance was observed in films containing 10% extract. SEM analysis revealed smooth, homogeneous, and defect-free surfaces, whereas FTIR and DSC analyses suggest strong intermolecular interactions leading to improved thermal stability and matrix cohesion. The immobilized 3-deoxyanthocyanidins exhibited pH-dependent color responses across a pH range of 1-12 and maintained their coloration under alkaline conditions, reflecting their inherent stability. However, the gradual color transitions indicate greater suitability for active antioxidant packaging than intelligent pH-indicator applications. Moreover, 10% extract-loaded films represent the most promising candidates due to their superior functional performance. The incorporation of sorghum glume extract transformed chitosan films into active bio-based systems with enhanced antioxidant protection, improved light barrier properties, and maintained physicochemical stability.