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

In the present study, methylcellulose-based pH sensitive flms were developed by incorporating onion peel extract. The efect
of onion peel extract containing anthocyanin (OPEA) on the structural, mechanical, thermal, and antioxidant properties of
methylcellulose flms 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 flms were fabricated by the solution casting method. The Fourier transform infrared (FTIR)
analysis indicated broad peaks of O–H stretching at 3300 cm−1 confrming the presence and intermolecular interaction of
anthocyanin with the polymer matrix. Scanning electron microscopy (SEM) analysis indicated the heterogeneous and irregu�lar surface patterns of flms 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 afected signifcantly.
The OPEA substituted methylcellulose flms were tested for radical scavenging activity indicating an increase in the anti�oxidant potential by 75% for the highest concentration of the flms. Color change was observed for the flms from pink to
green/yellow with the increase in pH. The developed smart flms may be used for packaging food rich in fats and proteins.