Confirmation of the unexpected occurrence of bitterness-inducing cucurbitacins in edible unripe melons by a two-step workflow based on liquid chromatography with combined UV and high-resolution MS detection

Plant metabolites known as cucurbitacins are known to impart an unpleasant bitter taste to edible fruits and even lead to severe health complications after the ingestion of relatively high amounts. In this study, an analytical method based on reversed phase liquid chromatography with combined detection by UV spectroscopy and atmospheric pressure chemical ionization high-resolution single/tandem mass spectrometry was applied to confirm the occurrence of four cucurbitacins (B, D, and R, and 23,24-dihydro cucurbitacin B) previously inferred in unexpectedly bitter-tasting fruits of an Italian variety (Scopatizzo) of unripe melon (Cucumis melo L.), known for the sweetness of its fruits. The method also unveiled the occurrence of eleven different cucurbitacins in not edible fruits of "exploding (squirting) cucumber" (Ecballium Elaterium L.), a well-known natural source of cucurbitacins. The unexpected occurrence of cucurbitacins in Scopatizzo fruits warrants further investigation into the factors triggering their biosynthesis, to help preventing both economic losses for farmers and potential health risks for consumers.