From Rice Grain to Rice Bran: Processing Effects on Nutrient Retention, InVitro Bioaccessibility and Caco-2 Cellular Absorption of Bioactive Compounds

Rice (Oryza sativa L.) is a globally consumed staple food, commonly in its white rice form. However, milling processes such as dehusking and polishing remove nutrient-dense outer layers, causing significant losses of key compounds like vitamin E, minerals, and other bioactives (i.e. γ-oryzanol and polyphenols). This study evaluated the impact of rice milling on nutrient retention in 11 rice samples from subspecies Indica, Aromatic, and Japonica grown in Costa Rica, and for selected samples examined the in vitro bioaccessibility and Caco-2 cellular absorption of major bioactive compounds in rice bran. Samples were processed into white rice and rice bran and analyzed for vitamin E (tocopherols and tocotrienols) and mineral content. White rice contained 66% less vitamin E and 75% fewer minerals than bran, and no clear association was observed between degree of milling and vitamin E loss, suggesting that variation in nutrient retention is more closely related to intrinsic sample characteristics than to milling degree. The in vitro digestion followed by Caco-2 cell assays was used to measure bioaccesibility and absorption of γ-tocotrienol, γ-oryzanol, and ferulic acid from bran. Ferulic acid demonstrated the highest digestive stability, solubility, bioaccesibility (186–1159%) and absorption (0–20%). Γ-Oryzanol showed moderate bioaccesibility (59–162%) and uptake (maximum 0.1–0.7%), likely due to its esterified form, while γ-tocotrienol, though bioaccesible (32–241%), had no detectable absorption. These results confirm rice bran as a valuable source of bioavailable antioxidants and underscore the need to optimize processing methods to retain its nutritional properties.