Profiling cucurbitacins from diverse watermelons (Citrullus spp.)

Cucurbitacins are a group of tetracyclic triterpenes produced by members of the Cucurbitaceae family that are known for their bitter taste, and have both positive and negative attributes based on their use. The aim of the present study was to profile cucurbitacins through the quantitative analysis of diverse watermelon (Citrullus spp.) germplasms, including Citrullus colocynthis and Citrullus lanatus, using liquid chromatography-mass spectrometry (LC-MS) and high performance liquid chromatography. We isolated cucurbitacins B and E, and cucurbitacin E glycoside and evaluated the concentration of these compounds in watermelon leaves, fruits, and seedling extracts. High amounts of cucurbitacin E glycosides were found in most of the C. colocynthis leaves at concentrations between 1.3 and 0.9 mg/g of fresh weight, while relatively low concentrations of cucurbitacin B and E were detectable in these tissues. Interestingly, cucurbitacin E glycosides were only detected in most C. colocynthis fruits at concentrations between 0.21 and 3.2 mg/g fresh weight. We also confirmed the correlation between bitter taste and cucurbitacin E glycoside content. Cucurbitacin B and E and cucurbitacin E glycoside were found in most of the cultivars tested, while cucurbitacin agylcones were the primary cucurbitacins identified in seedlings. This study reveals the cucurbitacin composition in various watermelon germplasms and in different plant tissue.