Abstract
We measured the concentration of antioxidant phenolic compounds and the hydrophilic oxygen radical absorbance capacity (H-ORAC) of extracts from the grains of colored rice varieties grown in two areas of Japan (Rikuzentakada and Daisen) with distinctly different climatic conditions in summer. The accumulated temperature from eleven days to twenty days after heading of rice grown in the Rikuzentakada area was lower than that experienced by the same varieties grown in the Daisen area. The differences in the accumulated temperature ranged from 14.5°C (variety Oumurasakimochi 422) to 27.9°C (variety Okunomurasaki ). The concentration of anthocyanin and cyanidin 3-glucoside in two varieties of waxy black rice grown in Rikuzentakada were higher than that of the same varieties grown in Daisen. The concentration of proanthocyanidin in all varieties of brown rice was also higher when grown in Rikuzentakada than in Daisen. The H-ORAC values of these colored rice varieties grown in Rikuzentakada were higher than those grown in Daisen. The content of protocatechuic acid, which has high radical-scavenging activity, in the total phenolic acid extracts of colored rice was higher in the grains grown in Rikuzentakada than in Daisen. These results demonstrate that low temperatures due to different growth climatic conditions stimulate the production of antioxidant compounds such as anthocyanin and proanthocyanidin, leading to an increase in antioxidant activity in the grains of colored rice varieties.
