cucurbitacin C

Cucurbitacin C is a triterpene-class compound contained in fruit and leaf tissues of cucumber (Cucumis sativus). A 2007 academic journal positions this compound as a bitter principle in cucumber plants.

That article states the detection threshold for cucurbitacin C's bitterness is less than 0.1 mg/L, and that the bitterness sensed when biting cucumber parts may correspond to this compound's content. The detailed methodology of threshold measurement—panel size, measurement method, and others—is not stated in this brief article.

A 2014 study identified 9 genes and 4 catalytic steps in the biosynthesis pathway of cucurbitacin C, and reported two regulatory factors: Bt (Bitter Fruit), which controls expression in fruit, and Bl (Bitter Leaf), which controls expression in leaves. A 2015 article explaining this research describes how, during domestication, a mutation arising in the promoter region of Bt was selected for and fixed, reducing Bt expression in fruit and shutting down this biosynthesis pathway, while Bl maintained its expression in leaves. The former is an abstract-level report based on genomic comparison, and the explanatory article itself does not have its own experimental data.