Development and characterization of biodegradable active films based on rice starch with nanocellulose and Amaranthus viridis extract

This study investigated the incorporation of Amaranthus viridis (AV) extract into films composed of rice starch (RS) and nanocellulose (CNF) at concentrations of 5 %, 7.5 %, and 10 %, aiming to evaluate the effects on physicochemical, mechanical, and antioxidant properties. The addition of AV increased the films' structural density, especially at 10 %, which showed a compact surface with no visible pores and characteristic specks related to mineral salt crystallization (calcium, iron, magnesium) interacting with oxalates to form insoluble complexes. Fourier-transform infrared spectroscopy (FTIR) analysis confirmed interactions between extract compounds and the polymer matrix. Thermal stability improved with more extract, with degradation peaks reaching 420 °C at 10 % AV. Water solubility increased from 28 % (RS + CNF) to 37 % (10 % AV), while water holding capacity decreased from 42 % to 26 %. Film thickness decreased from 80 μm to 50 μm. Regarding mechanical properties, tensile strength rose to 6.5 MPa at 5 % AV, and elongation at break reached 145 % with 10 % AV, indicating increased flexibility. Antioxidant activity improved with higher AV levels, with the 10 % film presenting the best performance: FRAP (499.10 μg/mL), phosphomolybdenum method (372.42 mg AAE/g), ABTS (26.52 % RSA), and DPPH IC₅₀ (27.42 μg/mL). All formulations exhibited biodegradability, with mass loss above 80 % after 15 days of soil exposure. In conclusion, the incorporation of Amaranthus viridis extract, particularly at 10 %, enhanced the films' structural, mechanical, and antioxidant properties, confirming its potential for use in active and biodegradable packaging.