Chemical profiles and antioxidant properties of roasted rice hull extracts in bulk oil and oil-in-water emulsion

We conducted in vitro assays to investigate the antioxidant properties of aqueous or ethanolic extracts of roasted rice hulls. Phenolic compound contents were analyzed via HPLC, and comprehensive chemical profiles were obtained via 1H NMR and 1H-H COSY NMR. Rice hulls were roasted at 150, 180, and 230 °C for 20 min, after which the aqueous and 70% ethanol extracts were obtained. In vitro assays showed that rice hulls roasted at 230 °C possessed very strong antioxidant properties (p < 0.05). Comprehensive chemical profiles determined via NMR showed that roasting increased the contents of specific amino acids and monosaccharides and reduced the organic acid contents. p-Coumaric, vanillic, and ferulic acids were the most dominant phenolic compounds present in the sample. Added roasted rice hull extracts enhanced the oxidative stability of bulk oil and in O/W emulsions at 60 °C. However, the extracts accelerated lipid oxidation rates of oils heated at 180 °C.