Valorization of agar extracted from Gelidium elegans via ultrasound-assisted extraction as potential film packaging by optimizing the incorporation of chitosan and curcumin

This study characterized agar extracted from Gelidium elegans using ultrasound-assisted extraction (UAE) compared with conventional extraction (CV). The CV yielded significantly higher agar (21.50 %) than UAE (17.91 %); however, both methods produced stable agar with high melting temperatures (90.00 °C and 86.67 °C) and low moisture content (MC) (12.06 % and 14.94 %), respectively. UAE agar exhibited higher gel strength (218.58 g·cm-2) and gelling temperature (36.00 °C), desirable color, and lower sulfate content (0.46 %). UAE agar was further applied to optimize agar-based composite films as alternatives toward plastic packaging by incorporating varying levels of chitosan (0.5-1.0 % w/v) and curcumin (0.04-0.10 % w/v). Film properties including water vapor permeability (WVP), oxygen permeability (OP), MC, solubility, transparency, and 2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant activity were evaluated using response surface methodology-central composite design (RSM-CCD). The model was validated, and the optimum formulation was chosen based on highest desirability (0.9096) at 0.5 % (w/v) chitosan and 0.07 % (w/v) curcumin. The optimized film exhibited WVP (2.38 × 10-10 g/msPa), OP (4.28 × 10-7 g/ms), MC (13.71 %), solubility (29.19 %), transparency (9.93), and DPPH activity (60.77 %), all within specified prediction ranges. These findings demonstrate that agar-based composite films incorporating with chitosan and curcumin provides good validation of model prediction and hold strong potential for eco-friendly food packaging applications.