Development and functional characterization of psyllium-sorbitol-WSPI-spirulina composite edible films for...

This study develops and characterizes psyllium-sorbitol-WSPI-Spirulina composite edible bioplastic films, formulated using a multicomponent matrix in which psyllium mucilage and sorbitol provide the structural base while wheat-straw protein isolate (WSPI) and Spirulina platensis supply functional reinforcement and bioactive properties. A Box-Behnken experimental design evaluated the combined effects of WSPI (3-6% w/w), Spirulina (0.5-2.0 g/L), and glycerol (30-40% w/w) on the mechanical, barrier, optical, solubility, biodegradability, and bioactive responses of the composite films. TS and EAB ranged from 6.54 to 9.46 MPa and 7.02 to 13.59%, while WVP varied between 6.80 and 10.24 g·m⁻¹·s⁻¹·Pa⁻¹. Glycerol enhanced flexibility, transparency, solubility, and biodegradability, whereas higher Spirulina levels improved elasticity, antioxidant capacity, and antimicrobial activity. The optimized formulation (6% WSPI, 2 g/L Spirulina, 30% glycerol) achieved a TS of 8.69 MPa, an EAB of 12.42%, a WVP of 7.20 g·m⁻¹·s⁻¹·Pa⁻¹, and 70.8% biodegradation within 7 days. FTIR confirmed intensified hydrogen bonding, TGA indicated delayed thermal decomposition, and SEM revealed a compact, homogeneous morphology. Overall, the structural, functional, and biodegradation profiles demonstrate that integrating WSPI from agricultural waste with Spirulina bioactives yields a mechanically robust, antioxidant, antimicrobial, and rapidly biodegradable edible film. These outcomes align with the discussion and highlight the film's strong potential as a circular, sustainable, and functional alternative for food-packaging applications.