Incorporation of natural antioxidants from rice straw into renewable starch films

Abstract

This study showed that rice straw waste is a valuable source for the extraction of water-soluble phenolic compounds that can be successfully incorporated into bioactive starch-based films. The major phenolic compounds in the extract were identified as ferulic, p-coumaric and protocatechuic acid using UHPLC-MS. Homogeneous films with antioxidant properties were produced by melt blending and compression molding and the changes in the physico-chemical properties were evaluated. The produced antioxidant starch films were slightly reddish-colored and exhibited good in-vitro antiradical scavenging activity against DPPH*. The addition of the antioxidant extract improved the oxygen barrier properties without negatively affecting the thermal and the water vapor barrier properties. However, antioxidant starch films turned more brittle with increasing amount of the antioxidant extract, which was probably due to interactions of phenolic compounds with the starch chains. The film forming process induced chain scission of starch molecules in all films, shown in a decrease in molecular weight of native starch from 9.1 × 106 Da to values as low as 1.0–3.5 × 106 Da. This study aids a circular economy by recycling rice straw for the production of bioactive food packaging.