Effect of Popping and Steam Cooking on Total Ferulic Acid, Phenolic and Flavonoid Contents, and Antioxidant Properties of Sukhothai Fragrant Black Rice

This study investigated the effects of thermal processing and extraction solvents on the phytochemical composition, antioxidant potential, and cytotoxic activity of Sukhothai fragrant rice (Oryza sativa L.). Rice subjected to three processing methods, unprocessed (raw), popped/puffed and steam-cooked, was extracted using hot water or 70% (v/v) ethanol, yielding six extracts. Trans-ferulic acid, γ-oryzanol and anthocyanins were quantified using HPLC-DAD and HPLC-ESI-MS, while total phenolic and flavonoid contents, and antioxidant activities were evaluated using Folin–Ciocalteu, aluminium chloride, DPPH and ABTS assays. Cytotoxicity was assessed in Huh7 hepatocellular carcinoma cells. Water extracts consistently produced higher yields and contained greater total phenolic, flavonoid and anthocyanin contents, resulting in stronger antioxidant activity. Unprocessed rice water extract exhibited the highest trans-ferulic acid recovery and antioxidant capacity. Thermal processing, particularly steamed cooking, markedly reduced phytochemical contents, likely due to heat-induced degradation. In contrast, ethanolic extracts yielded lower quantities but higher concentrations of less polar bioactive compounds and exhibited greater cytotoxic effects. Overall, minimal thermal processing combined with aqueous extraction best preserved antioxidant compounds, while ethanolic extraction enhanced biological potency. These findings highlight the importance of processing intensity and solvent polarity in optimizing the nutraceutical and functional potential of black rice.