Studies on the relationship between antioxidative activity of rice hull and germination ability of rice seeds

An investigation of the germination potentials of seeds of Indica and Japonica rice varieties revealed that while the long‐life rice seeds retained the germination ability even on storage for a year at 30°C, the germination ability of the short‐life rice seeds tended to decrease when stored beyond 6 months. The role of rice hull constituents in the preservation of the germination property during ageing of rice seeds was investigated with special emphasis on rice antioxidants. Antioxidative assay with chloroform‐methanol and methanol‐water extracts of hull, bran‐germ and grain fractions of two Indica and five Japonica rice varieties indicated that all of the seed varieties belonging to Indica and Japonica possessed a strong antioxidative activity in the hull fraction. Hull extracts of long‐life rice seeds showed relatively higher activities than those of short‐life rice seeds. In contrast, hull extracts of long‐life rice seeds had higher inhibitory effects on lipoxygenase activity than did those of short‐life varieties. Quantification of the natural antioxidants indicated that α ‐tocopherol in rice oil to be present in the range of 318.3–450.1 μg g −1 oil while the amount of oryzanol in the hull, bran‐germ and grain fractions of rice was found to be 1.0–5.8, 95.4–279.8 and 3.0–9.4 μg g −1 sample respectively. The results, however, did not show any positive correlation between the amount of natural antioxidants in rice hull and germination potentials of rice seeds. The amount of total phenolic constituents in rice hull was found to range from 190–390 μg g −1 sample, the levels being far higher in long‐life rice seeds in comparison with the short‐life rice seeds. These values seemed to agree well with the germination data of the corresponding rice variety. The investigation revealed a strong influence of the level of phenolic constituents in rice hull on the storability of rice seeds.