Motivations to produce biofuels from rice bran: An overview involving a recent panorama

Rice bran is a brownish powder layer that covers the rice grain, being a co-product generated during the grain milling process and is usually underused for animal feed or burned as a low-cost fuel. However, comprising between 5 and 10 wt% of the rice grain, this biomass is a source of minerals, fatty acids, fiber and sterols, containing also up to 25 wt% of oil. Because it contains an active lipase in its composition that hydrolyses its triglycerides into free fatty acids, crude rice bran oil typically contains a high acidity that makes its consumption unfeasible. Moreover, the defatted or de-oiled biomass is a lignocellulosic material which, through an adequate pre-treatment to reduce its recalcitrant structure, can be used in different sector, especially to produce biofuels. Given its functionality, this review describes recent scientific approaches to how rice bran is being used to prepare biofuels (mainly biodiesel from rice bran oil, or bio-oil, biochar, biogas, biohydrogen, bioethanol, and biobutanol from defatted biomass). Furthermore, the properties and characteristics that motivate the use of this material to synthesize fuels are reviewed, the main pre-treatment techniques necessary to remove part of the lignin from its lignocellulosic matrix and allow the digestibility of cellulose and hemicellulose as well as the challenges for the expansion as an energetic feedstock.