Development of chitosan films with Sideritis congesta essential oil and hazelnut shell extract

Chitosan films were formulated with 0.25-1% Sideritis congesta essential oil (SCEO) v/v and 2.5-10% hazelnut shell extract (HSE) v/v. Assessments were based on physical properties, phenolic content, antioxidant activity, and mechanical properties. The mechanical properties were significantly influenced by the additives; compared to control films (Tensile Strength (TS): 94.35 MPa; Elongation at Break (EAB): 62.86%), the incorporation of 10% HSE enhanced flexibility (EAB: 69.66%), whereas 1% SCEO reduced mechanical strength (TS: 39.44 MPa). However, additives dramatically improved bioactive performance compared to the low activity of control films (Total Phenolic Content (TPC): 2.67 mg GAE/g; 1,1-diphenyl-2-picrylhydrazyl (DPPH): 6.66%; 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS): 9.31%). The film with 1% SCEO demonstrated the highest bioactivity (TPC: 19.46 mg GAE/g; DPPH: 34.18%; ABTS: 44.32%), followed by 10% HSE (TPC: 13.54 mg GAE/g; DPPH: 23.79%; ABTS: 35.69%). Optical properties also shifted significantly; compared to clear Control films (L*=16.54, a*=–1.93, b*=1.99), HSE-10 films were darker (L*=9.86, a*=–0.59, b*=–0.04), while SCEO-1 appeared greenish-yellow (L*=33.24, a*=–3.16, b*=11.66). Consequently, the formulation containing 10% HSE was deemed optimal for applications requiring flexibility, while the 1% SCEO formulation was identified as the most effective for oxidation-sensitive high-fat foods due to its superior antioxidant capacity, despite the reduction in mechanical strength.