Valorization of black rice as an antioxidant raw material

Rice is one of the most consumed grain in the world. Moreover, there are many kinds of it, and each one has a singular composition and properties, such as the black rice. Thus, the aim of this work was to evaluate the chemical composition of black rice grains and their antioxidant activity. Black rice grains were obtained in Dourados/MS/Brazil and characterized by analyzes of moisture, ash, lipid, protein, carbohydrate, water activity, phenolic compounds and antioxidant activity (by DPPH and ABTS methods). Extracts with methanol 50%, acetone 70% and distilled water were made to determine phenolic compounds and antioxidant activity. Black rice have presented a moisture content of 8.41 ± 0.01%, and it follows the Brazilian legislation (<14%). The ash content of black rice (1.66 ± 0.01%) is higher than white rice (0.54 ± 0.07%). It can suggest that this grain could be considered a source of minerals important in human diet. The studied raw materials have presented 0.35 ± 0.04%, 8.52 ± 0.33%, and 80.86 ± 0.09% of lipid, protein and carbohydrate, respectively. In addition, the water activity was 0.5615 ± 0.0055. Which indicates a microbiological stability. The phenolic compounds content of black rice grains were 122.05 ± 0.01 mg EAG/100 g. It is around six times higher than the content on white rice (18.03 ± 0.01 mg EAG/100 g). The antioxidant activity resulted in 3.28 ± 0.26 g/g DPPH and 24.22 ± 0.03 μM trolox/g. As well as phenolic compounds content, the antioxidant activity for black rice is greater than white rice (101.95 ± 0.05 g/g DPPH and 1.85 ± 0.05 μM trolox/g, for DPPH and ABTS methods respectively). According to these results, we can conclude that black rice is a grain that may be better explored and used, due to its great chemical composition and antioxidant activity.