Starch-Rich Rice By-Products as a Renewable Resource for Sustainable Production of Flexible, Water Tolerant, Antioxidant, and UV-Protective Bioplastics

Abstract

The development of multifunctional materials from agrifood residues supports circular bioeconomy strategies by reducing waste and promoting renewable feedstocks. This study investigates rejected rice dust (RD) and colored rice (CR), two starch-rich rice processing by-products, as alternative sources for natural starch-based bioplastics, using purified rice starch (PRS) as a benchmark. RD and CR contained 79.9% and 82.9% total carbohydrates (48.6% and 51.8% starch), versus 98.3% carbohydrates and 70.2% starch in PRS. CR exhibited the highest amylose (29.5%) and phenolic content (20.9 mg GAE/100 g), compared to RD (21.3%; 8.8 mg GAE/100 g) and PRS (15.8%; 2.3 mg GAE/100 g). Gelatinization peak temperatures are elevated in RD (74.2°C) and CR (73.9°C) versus PRS (66.7°C). RD-based films showed mechanical strength (5.4 MPa) and modulus (146 MPa) comparable to PRS (5.5 MPa; 175 MPa), while CR-based films have lower modulus (53 MPa) but greater elongation at break (20.2%). Contact angles are highest in CR (119°), followed by PRS (102°) and RD (70°). Antioxidant activity reached 88% (CR), 33% (RD), and 10% (PRS). Only CR-based films provided UV-B protection. These results highlight RD and CR as renewable matrices for producing environmentally sustainable, functionally enhanced starch-based materials for packaging and coating applications.