In vitro digestion of protein aerogels generated from defatted rice bran protein via supercritical carbon dioxide technology

Rice bran (~8-10% of total grain weight), a rice processing byproduct, is a rich source of macro- and micro-nutrients. Defatted rice bran (DRB) contains high-value compounds, i.e., starch and protein. Despite its high nutritive value, DRB is being discarded as a waste or used as an animal feed or composite material, creating a serious concern for the rice industry. Therefore, this study aimed to investigate the in vitro digestibility of protein aerogels produced from DRB using supercritical carbon dioxide (SC-CO2) drying (10MPa, 40℃, and 1L/min CO2 flowrate). SC-CO2 drying preserves the nanoporous structure with minimum shrinkage, capillary stress, and surface tension. The DRB contains 13.84 ± 0.11 g/100 g DRB of protein and was used at different concentrations (10, 15, and 20%) to form aerogels. They were characterized for their morphology, crystallinity, chemical structure, textural properties, and solubility, and the formed aerogels were used for in vitro digestion (oral, gastric, intestinal, and sequential). All concentrations revealed three-dimensional open porous structure. However, the concentration was optimized to 15% showing better ability to form a strong gel, and the concentration >15% led to a denser structure with higher viscosity. The highest surface area (40 m2/g), pore size (18 nm), pore volume (0.23 cm3/g), porosity (87%), and ultra-low density (0.19 g/cm3) were achieved using 15% concentration. Gelation resulted in a noticeable reduction in crystalline peaks and increase in hydrogen bonding in aerogels. Furthermore, the protein aerogel revealed higher hydrolysis as compared to protein extract due to reduced crystallinity. Additionally, the protein aerogel showed a hydrolysis of 77% after sequential digestion, which is higher as compared to separate oral ( < 1%), gastric (20%), and intestinal (26%) phase digestions. Overall, this study highlights the potential of rice bran protein as a promising source for functional food formulations while increasing the sustainability of rice production.