Seasonal Changes in Flavonoid Content in Flavedo of Ponkan (Citrus reticulate Blanco) and Tachibana (Citrus tachibana Tanaka)

Changes in the polymethoxyflavone (nobiletin, tangeretin, and sinensetin) and hesperidin contents in flavedo of Ponkan (Citrus reticulata Blanco) and Tachibana (Citrus tachibana Tanaka) during cultivation from July to December were investigated over several years. In 20 surveys conducted over 3 years (Ponkan) and 2 years (Tachibana), the nobiletin, tangeretin, sinensetin, and hesperidin content (mg・100 g–1FW) was the highest in July and decreased significantly in the harvest period. Over the three years investigated, the nobiletin content in flavedo of Ponkan in December was 74, 46, and 40% of that in July, respectively. The nobiletin content in the flavedo of each fruit significantly increased with flavedo growth in 2017. In contrast, the nobiletin content did not increase in 2018. This could have been due to higher nobiletin degradation rather than flavedo growth. These results indicate that harvesting times of July, August, and September, earlier than common harvesting times could be more efficient time for the extraction and utilization of flavonoids. The relationship between the flavonoid content in the flavedo and fruit growth (maturity) as well as climatic factors remain to be elucidated.