Composição química e propriedades antioxidantes de grãos de arroz com pericarpo marrom-claro, vermelho e preto

Abstract

Rice (Oryza sativa) stands out as an important food, considering production and consumption. Although the rice usually cultivated in most countries is the one with light-brown pericarp color, there are other grains with red and black pericarp color, used for food in some regions of the world. The consumption of these grains is mainly related to their organoleptic characteristics, but some researches demonstrate that they can also present nutritional differences compared to light-brown color rice grains. So, the present research aimed at evaluating the chemical composition, the antioxidant characteristics and the physiological effect on rats, of rice grains with light-brown, red and black pericarp color, from recommended genotypes and weedy rice, for their utilization in the diet. The grains were obtained in the 2006/07 growing season, under equal conditions, in the experimental area of Universidade Federal de Santa Maria, RS. For the evaluation of the chemical composition the contents of total carbohydrates, amylose, fiber, protein, lipids, mineral matter and minerals were determined in brown rice grains. The antioxidant characteristics were determined from the concentration of total soluble phenolic compounds (TSPC) and the antioxidant activity (AOA), evaluated in grains with different processing (brown, polished, parboiled brown and parboiled polished; raw and cooked). By a bioassay, with healthy Wistar male rats fed diets containing brown rice grains with light-brown, red or black pericarp color, or a control diet, the effect of the consumption of these grains was evaluated. Body weight gain, feed consumption, epididymal fat pad, blood concentration of glucose, triglycerides, total cholesterol and HDL cholesterol, activity of the enzymes superoxide dismutase (SOD) and glutathione peroxidase in the liver, and lipid peroxidation in the blood and liver were determined. The results showed significant difference in the chemical composition among grains with light-brown, red and black pericarp, mainly in the content of fiber and minerals, and some genotypes with red and black pericarp stood out with higher concentration of some of the components evaluated, like protein and minerals. In the antioxidant characterization, significant difference was observed in the concentration of TSPC and AOA among genotypes, with the higher values for grains with red and black pericarp color, with positive and significant correlation between these parameters. Parboiling reduced the concentration of TSPC in the grains, with reduction in the AOA. In a similar way, cooking of the grains also reduced the concentration of TSFC, especially in brown and polished grains. In the bioassay, no significant effect of the diets containing rice grains was observed for most of the evaluated parameters, with effect only on the weight of the epididymal fat pad and on the activity of SOD in the liver, but with no difference among rice types. The increase in the activity of SOD may indicate possible reduction in the oxidative stress of the organism, but more research is necessary.