Cucurbitacin C^|^mdash;Bitter Principle in Cucumber Plants

Cucumber plants contain a bitter substance, cucurbitacin C. The compound was isolated from cucumber leaves using preparatory HPLC (high performance liquid chromatography) to investigate the relationship between its content and bitterness of the plant parts. An analytical method for cucurbitacin C using HPLC was also established. A Japanese popular cultivar, 'Sharp 1' contained the compound in the leaves but not in the fruits, while a unique cultivar with white skin 'Shinsyo Hakuhi' contained it both in leaves and fruits. The stem end of 'Shinsyo Hakuhi' fruit contained higher amounts of it than other fruit parts. Cucurbitacin C is a strongly bitter component and its threshold level was less than 0.1 mg/L. The bitter sensation felt when biting the plant parts could be interpreted as corresponding to the content of cucurbitacin C.