Comparison of Proanthocyanidin Content in Rabbiteye Blueberry ( Vaccinium virgatum Aiton) Leaves and the Promotion of Apoptosis against HL-60 Promyelocytic Leukemia Cells Using 'Kunisato 35 Gou' Leaf Extract.

Polyphenol-rich rabbiteye blueberry ( Vaccinium virgatum Aiton) leaves have attracted attention as a food material. In this study, we compared the total polyphenols, total proanthocyanidin content, and antioxidant activity of the leaves of 18 blueberry varieties and investigated the seasonal variation in polyphenols. We also evaluated the anti-cancer cell proliferation properties of the rabbiteye blueberry leaf specific cultivar 'Kunisato 35 Gou'. Rabbiteye blueberry leaves had significantly higher total polyphenol and total proanthocyanidin values than northern highbush blueberry and southern highbush blueberry leaves. The antioxidant activity of blueberry leaves was highly positively correlated with both the total polyphenol and total proanthocyanidin content. Variations were observed in the total polyphenol and total proanthocyanidin content of rabbiteye blueberry leaves harvested at different points in the growing season; leaves collected in fall to winter contained more epicatechin in addition to proanthocyanidins. In the evaluation of anti-cancer cell proliferation properties against HL-60 promyelocytic leukemia cells, the September-harvested extracts of rabbiteye blueberry 'Kunisato 35 Gou' showed strong properties, and the use of an FITC Annexin V apoptosis detection kit with propidium iodide confirmed that this HL-60 cell death occurred via apoptosis. Limiting the harvest time would make rabbiteye blueberry leaves a more functional food ingredient.