Effect of Onion Peel Extract on Structural, Mechanical, Thermal, and Antioxidant Properties of Methylcellulose Films

In the present study, methylcellulose-based pH sensitive films were developed by incorporating onion peel extract. The effect of onion peel extract containing anthocyanin (OPEA) on the structural, mechanical, thermal, and antioxidant properties of methylcellulose films was investigated. The OPEA was analyzed for total monomeric anthocyanin content (TMAC) and total phenol content (TPC) containing 56.91 ± 2.52 mg/L and 0.17 ± 0.00 g/L, respectively. DPPH (2, 2-diphenyl-1-picrylhydrazyl) free radical scavenging method and FRAP method showed that OPEA presented higher antioxidant activity than commercial antioxidant butylated hydroxytoluene (BHT). OPEA exhibited a visual color change from pink to green/yellow with a change in pH from 1 to 14. The smart films were fabricated by the solution casting method. The Fourier transform infrared (FTIR) analysis indicated broad peaks of O–H stretching at 3300 cm⁻¹ confirming the presence and intermolecular interaction of anthocyanin with the polymer matrix. Scanning electron microscopy (SEM) analysis indicated the heterogeneous and irregular surface patterns of films because of the addition of OPEA which increased with the increase in the extract concentration. However, with the incorporation of OPEA, the tensile, elongation, and thermal properties were not affected significantly. The OPEA substituted methylcellulose films were tested for radical scavenging activity indicating an increase in the antioxidant potential by 75% for the highest concentration of the films. Color change was observed for the films from pink to green/yellow with the increase in pH. The developed smart films may be used for packaging food rich in fats and proteins.

Graphical Abstract