Bioactive Chitosan Films from Shrimp and Crab Shells: Physicochemical and Functional Properties Associated with Biological Source and Processing History

Chitosan films are promising materials for food-related applications, but their performance depends on polymer characteristics. This study compared films from hybrid chemical–microbiological shrimp (CM-Shr) and crab (CM-Crb) chitosans, chemically extracted crab chitosan (Ch-Crb), and high- (Ref-H) and low-molecular-weight (Ref-L) reference chitosans. Films were prepared using 1.5% (w/v) chitosan in 1% (v/v) acetic acid with glycerol at 30% (w/w, relative to dry chitosan). Chitosans were characterized by degree of deacetylation, molecular weight, moisture, ash, nitrogen and ATR-FTIR; films were assessed for thermal, morphological, hydration, mechanical, optical, and antibacterial properties. ATR-FTIR indicated differences in amino, residual N-acetyl, and hydrogen-bonded environments. At 15 min, CM-Crb and Ch-Crb exhibited lower apparent water absorption (34.5 ± 1.2% and 32.6 ± 0.7%) than Ref-H (51.8 ± 1.9%). Antibacterial inhibition beyond the 6 mm film-disk diameter was absent at 1.5% and predominantly detected for CM-Crb and Ch-Crb at 3.0–4.5% (w/v) chitosan in the film-forming solutions. CM-Crb exhibited tensile strength of 52.1 ± 4.3 MPa, the highest elongation at break (3.7 ± 0.3%) and UV blocking at 340 nm (35%). Film performance was associated with the physicochemical profiles and processing history of the starting chitosans.