A short review of green extraction technologies for rice bran oil

Rice is one of the most important crops throughout the world, as it contributes toward satisfying the food demand of much of the global population. It is well known that rice production generates a considerable number of by-products, among which rice bran deserves particular attention. This by-product is exceptionally rich in nutrients, since it contains a wide spectrum of macronutrients (proteins, fats, carbohydrates) as well as dietary fibers and bioactive compounds. However, rice bran is usually wasted or just used for the production of low-cost products. The lipidic fraction of rice bran contains an unsaponifiable fraction that is rich in such functional components as tocopherols, gamma-oryzanol, tocotrienols, and phytosterols. This lipidic fraction can be extracted to obtain rice bran oil (RBO), a high value-added product with unique health properties as a result of its high concentration in gamma-oryzanol, a powerful antioxidant mixture of bioactive molecules. Conventional extraction methods employ hexane as the solvent, but these methods suffer from some drawbacks linked to the toxicity of hexane for humans and the environment. The aim of the review presented herein is to point out the new green technologies currently applied for the extraction of RBO, by highlighting reliable alternatives to conventional solvent extraction methods that are in line with the twelve principles of green chemistry and a circular economy.