Improvement of starch films for food packaging through a three-principle approach: Antioxidants, cross-linking and reinforcement.

This study uses sunflower hulls, a by-product from the sunflower snack industry, to recover both, valuable phenolic compounds and cellulose fibers, for the production of antioxidant reinforced starch films as potential food packaging material. The phenolic extract provided antioxidant properties to the films with EC50 values of 89 mg film/mg DPPH. The cellulose fibers reinforced the starch films with a threefold increase in Young´s modulus. Furthermore, citric acid was added to induce cross-linking of the starch polymers and improve film integrity. The addition of citric acid induced both, starch polymer hydrolysis and cross-linking, seen in a shift in chain-length distribution after debranching with iso-amylase. This is the first study that focuses on a three-principle approach to improve edible starch films, and follows UN goals on sustainability to reduce waste and increase value in by-products as a step forward to functionalize packaging material.

Incorporation of natural antioxidants from rice straw into renewable starch films.

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.

Antioxidant starch films containing sunflower hull extracts.

This study explores the preparation of antioxidant starch food packaging materials by the incorporation of valuable phenolic compounds extracted from sunflower hulls, which are an abundant by-product from food industry. The phenolic compounds were extracted with aqueous methanol and embedded into starch films. Their effect on starch films was investigated in terms of antioxidant activity, optical, thermal, mechanical, barrier properties and changes in starch molecular structure. The starch molecular structure was affected during thermal processing resulting in a decrease in molar mass, smaller amylopectin molecules and shorter amylose branches. Already 1-2% of extracts were sufficient to produce starch films with high antioxidant capacity. Higher amounts (4-6%) of extract showed the highest antioxidant activity, the lowest oxygen permeability and high stiffness and poor extensibility. The phenolic extracts affected predominantly the mechanical properties, whereas other changes could mainly be correlated to the lower glycerol content which was partially substituted by the extract.