Novel flexible and active expanded-starch films enriched with Agrifood waste via microwave irradiation

Expanded materials possess valuable properties for food packaging, including thermal insulation and lightweight. However, developing sustainable alternatives with the potential to replace lightweight petroleum-based plastics is highly challenging. Starch biopolymer is a promising sustainable candidate due to its compostable character, great foamability and processability. Moreover, its chemical characteristics allow its combination with agrifood wastes to promote the circular economy and provide active properties. Most of the starch foams reported with low density are processed via extrusion and they are notably brittle and rigid, restricting their application. In this work, different expanded starch biocomposites, without or enriched with 40 wt.% orange peel (OP), were fabricated using 30 s of microwave (MW) irradiation, acquiring different properties depending on the main blowing agent used (i.e., water, sodium bicarbonate or expandable microspheres). These samples were fully characterized in terms of morphology, density, expansion degree, water uptake and solubility, mechanical properties, migration and antioxidant properties. Remarkably, the final expanded materials reached a considerably low density of 0.3 g/cm 3 and they exhibited exceptional flexibility, overcoming the important drawback of starch foams. Finally, the benefits of adding 40 wt.% of agrifood waste were not only environmental, but OP increased the expansion capacity and gave outstanding antioxidant properties.