抄録
Niihime fruit, produced in the coastal area of the Sea of Kumano in Mie prefecture, is a new sour citrus fruit. This is the first study to examine the characteristics of the flavonoids in niihime fruit. The content of flavonoids in the juice and peel of niihime fruit was determined by HPLC and their distribution was examined in comparison with seven other species of sour citrus fruits. Niihime fruit was found to contain a comparatively high quantity of bioactive flavonoids of the flavanone glycosides with rutinose sugar chain such as eriocitrin and hesperidin as well as the polymethoxyflavones such as nobiletin and tangeretin. The peel extract of niihime fruit exhibited comparatively high antioxidative activity among sour citrus fruits using the DPPH radical scavenging assay. Furthermore, the flavonoids eluted from niihime fruit by over time in hot and cold solutions of water, 5% ethanol, and 25% ethanol, which are commonly used in the field of food processing and cooking, were examined. The flavonoids eluted from niihime fruit in hot 25% ethanol solution was highest content in solutions, and the content of flavonoids eluted in 5min was an approximate half of content eluted in 60min. The flavanone glycosides, eriocitrin and hesperidin, were eluted in higher contents in hot solutions than in cold solutions. The polymethoxyflavones, nobiletin and tangeretin, were eluted to some extent in hot 5% ethanol but were found in low contents in cold solutions. The highest contents were eluted in hot 25% ethanol. The difference in the elution properties between flavanone glycosides and polymethoxyflavones is considered to be a result of their hydrophobic properties. The scavenging activity of DPPH radical for eluates was shown to increase over time, and the activity was suggested to be related to the elution content of eriocitrin, which is an antioxidant in niihime fruit. This study showed that niihime fruit contains a comparative abundance of bioactive flavonoids and these flavonoids are able to be eluted using hot solutions of water and ethanol.
