Extraction and analysis of antioxidant capacity in rice bran extracts from different Sarawak local rice varieties

Sarawak is blessed with many different local rice varieties. However, the nutritional contents and value-added processing possibilities of these local rice varieties remain underexplored. This research project was conducted to extract and assess natural antioxidant contents from rice bran of selected Sarawak local rice varieties. The rice bran extracts (RBE) were then further tested with in vitro chemical- and cell-based antioxidant assays preliminarily to evaluate their respective antioxidant capacities in alleviating oxidative injuries. The results revealed that RBE of different Sarawak local rice varieties contain significant amount of natural antioxidants. According to the current finding, Bajong LN RBE has the highest contents of phenolic compounds, flavonoids, and γ-oryzanol among all the tested samples. It was also discovered that higher average total phenolic, flavonoids, and tocotrienols contents were detected in RBE of Sarawak local rice varieties studied as compared to those in certain rice varieties cultivated elsewhere. In vitro chemical-based antioxidant assays further revealed the dose-dependent 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging capabilities of RBE to which the effectiveness differed among RBE of different local rice varieties. Among all the tested rice varieties, highest free-radical scavenging activity was detected with Bajong LN RBE and was significantly higher than that with RBE of commercial rice variety, MR219. Both Bajong LN and MR219 RBE were selected for in vitro cell-based antioxidant assay. Here, the H9c2(2-1) cardiomyocyte was used and the cellular induction effects with selected RBE and H2O2 were studied. Incubation of H9c2(2-1) with RBE and H2O2 showed dose-dependent cytotoxic effects respectively. Such observation revealed the potential prooxidant activity of RBE which consequently reduced cell viability at higher concentration. Cellular induction with safe dose range of RBE showed significant improvement in enzymatic activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in H9c2(2-1). Co-incubation of H9c2(2-1) with RBE and H2O2 further revealed the potential of RBE in alleviating H2O2-induced oxidative injuries as observed through a right shift in IC50 of H2O2. Higher increment in IC50 of H2O2 was detected with Bajong LN RBE as compared to MR219 RBE. Besides that, significant up-regulations in enzymatic activity and expression of CAT were also reported from H9c2(2-1) co-incubated with RBE and H2O2. As a summary, the present result put forward the potential of RBE as a source of antioxidants for alleviation of oxidative injuries in cardiovascular diseases (CVD). Additional studies are still required to further investigate the utilization of RBE as a strategy to combat oxidative stress-induced CVD.