Determination of phenolic compounds, flavonoids, and antioxidant activities in crude water extracts of Thai red and white rice cultivars

Pigmented rice varieties have been shown to exhibit strong antioxidant activity and to reduce oxidative stress implicated in various chronic diseases [1, 2]. The antioxidant activities of the water extract of brown rice or bran from two Thai rice cultivars: (i) Sang Yod, a red pigmented rice typically grown in Southern Thailand, and (ii) Dawk Mali 105, a commercial white-colored rice, were evaluated through chemical assays: DPPH radical-scavenging and inhibition of lipid peroxidation assays, as well as through cell-based assays: scavenging capacity of intracellular ROS in HL-60 cells using the fluorescent DCF and the NBT reduction. These assays have their specific mechanisms in detecting a particular mode of antioxidant actions. In the two chemical assays, all the rice extracts showed free radical scavenging and free radical chain breaking activities with EC₅₀ values ranging from 26 to 357µg/ml. Moreover, the cell-based assays detected ROS scavenging activities of these extracts with EC50 values in the range of 0.6–5mg/ml. All these assays indicated that the water extracts of Sang Yod exerted significantly higher antioxidant activity than those of Dawk Mali 105, which exhibited only moderate to low activity. Furthermore, high levels of antioxidant activity of the water extracts of Sang Yod were closely correlated to their flavonoid and phenolic contents, which were approximately 2.5 and 3 times higher, respectively, than those of Dawk Mali 105.

References: 1. Higashi-Okai, K. et al. (2008)J Uoeh. 30(4):37589.

2. Xia, M. et al. (2003)J Nutr. 133(3):74451.