Development and functional characterization of edible bioplastic films from Spirulina and protein isolate extracted from wheat straw (agricultural waste) for sustainable food packaging

This study develops and characterizes edible bioplastic films formulated from Spirulina platensis and wheat-straw protein isolate (WSPI) obtained from agricultural residues for sustainable food packaging. A Box–Behnken experimental design evaluated the effects of WSPI (3–6% w/w), Spirulina (0.5–2.0 g/L), and glycerol (30–40% w/w) on mechanical, barrier, optical, solubility, biodegradability, and bioactive responses. Films were assessed for tensile strength (TS), elongation at break (EAB), water vapor permeability (WVP), transparency, solubility, biodegradability, antioxidant activity, and antimicrobial inhibition, with complementary FTIR, TGA, XRD, and SEM analyses. TS and EAB ranged from 6.54 to 9.46 MPa and 7.02 to 13.59%, respectively, while WVP varied between 6.80 and 10.24 g·m⁻¹·s⁻¹·Pa⁻¹. Glycerol significantly increased EAB, transparency, solubility, and biodegradability, whereas higher Spirulina concentrations enhanced elasticity, antioxidant, and antimicrobial performance. The optimal formulation containing 6% WSPI, 2 g/L Spirulina, and 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 spectra confirmed intensified hydrogen bonding, TGA revealed delayed thermal decomposition, and SEM micrographs displayed a compact, homogeneous structure. These findings demonstrate that combining WSPI from agricultural waste with Spirulina bioactives can produce functional, biodegradable, and antioxidant edible films, supporting circular and sustainable food-packaging applications.