Development of γ-Oryzanol- and Tocopherol-Enriched Sunflower Oil from Rice Husk via Supercritical CO2 Extraction

Rice husk is an abundant agro-industrial by-product containing γ-oryzanol, tocopherols, and other antioxidant compounds with potential for food applications. This study investigated a supercritical CO2-assisted approach for directly transferring rice husk-derived antioxidants into stripped sunflower oil, using the oil as a food-grade receiving phase. A central composite design was used to investigate the effects of pressure and oil loading on γ-oryzanol recovery, tocopherol content, DPPH radical-scavenging activity, oil yield, and the rate of inhibition (Rinh). Multi-response optimization identified 232 bar and 30 g of stripped sunflower oil as a model-derived candidate condition within the investigated range. Under these conditions, the treated oil contained γ-oryzanol and tocopherols and showed higher assay-measured total phenolic and flavonoid contents than untreated stripped sunflower oil. HS-SPME-GC-MS indicated processing-associated changes in the volatile profile, including an increased signal for tentatively identified benzaldehyde and several oxygenated volatile signals. During heating at 180 °C in the absence of food, γ-oryzanol showed greater retention than total tocopherols, with 77.65% and 40.36% retained after 60 min, respectively. These results demonstrate the feasibility of using SC-CO2-assisted treatment to transfer rice husk-derived antioxidant compounds into sunflower oil, providing a potential approach for valorizing rice husk in edible-oil enrichment applications.