Antioxidant and antityrosinase activities in germinated brown rice of indigenous Thai cultivars

Abstract

The antioxidant and antityrosinase activities were examined in germinated brown rice of three indigenous Thai cultivars, namely Riceberry (purple), KDML 105 R-PSL-2 (red) and KDML 105 (white), which are commonly grown in Buriram province of Thailand. Germination was induced by steeping brown rice of each cultivar in distilled water (water: grain ratio = 2:1) at ambient temperature for 6 h. After low temperature induction at 8 – 10 ºC for 24 h, the rice kernels were allowed to germinate in a double-layered cotton cloth in the dark at ambient temperature for 0, 24 and 48 h, in which the antioxidant and antityrosinase activities of germinated brown rice were evaluated. The results revealed that germinated brown rice of all studied cultivars appeared to display higher levels of antioxidant and antityrosinase activities than ungerminated brown rice. The results showed 24-48 h germination regimes were most effective in maximizing the antioxidant and antityrosinase activities in germinated brown rice. Under such conditions, the maximum quantities of total phenolics, total flavonoids and antityrosinase were detected in Riceberry (25.06 mg GAE/g DW), KDML 105 R-PSL-2 (95.67 mg QE/g DW) and Riceberry (31.33%), respectively. Again, the highest DPPH value of 81.52% was detected in Riceberry and the highest ABTS value of 67.92% in KDML 105 RPSL- 2. Additionally, a strong correlation between antioxidant, antityrosinase and germination time was detected. The information obtained from this study should provide a foundation for future research aiming at the development of functional foods and/or cosmetics.