Generating nanoporous protein aerogels from defatted rice bran via supercritical carbon dioxide

Abstract: Rice bran (~8-10% of the total grain weight), a rice processing byproduct, is a rich source of macro- and micro-nutrients. To date, rice bran is commercialized for oil production, and the resulting defatted rice bran (DRB) is underutilized as an animal feed or composite material, creating disposal and economic loss concerns for the rice industry. Nevertheless, DRB contains a high amount of proteins. Therefore, the goal of this study was to convert DRB into high-value protein-based aerogels (i.e., nanoporous high-value materials for the delivery of bioactive compounds) using supercritical carbon dioxide (SC-CO₂) drying. Protein aerogels were produced from rice bran proteins and their fractions (i.e., albumin, globulin, glutelin, and prolamin). The extracted proteins from DRB were used at different concentrations (10, 15, and 20%, w/w) to form the aerogels. The generated aerogels were characterized for their morphology, crystallinity, chemical structure, textural properties, emulsifying properties, foaming properties, solubility, and in vitro digestibility. The DRB used for the extractions contained 13.8% (w/w) proteins. At the optimized conditions, the aerogels were produced using 15% (w/w) protein hydrogels at 10 MPa and 40 °C with a flow rate of 1 L/min. The protein aerogels produced at optimized conditions showed an open porous network structure with outstanding properties, such as surface area of 25 m²/g, pore size of 22 nm, pore volume of 0.11 cm³/g, and density of 0.11 g/cm³. The crystallinity of the proteins was reduced with the aerogel formation. No shifting in the location of characteristic absorbance regions was observed in the FTIR spectra. The properties of the aerogels from the rice protein fractions were also compared with that of the aerogels from whole protein extract. Overall, this research creates high-value novel ingredients from rice bran proteins that can be used to develop functional foods while increasing the sustainability of rice production.