Quantification of cucurbitacin C in bitter cucumber and its reduction by fermentation and acidification

Abstract

Cucurbitacins are seldom found in pickling cucumber, but when present, make finished products unpalatable. Liquid chromatography-time-of-flight mass spectrometry was employed to determine cucurbitacins in ‘Hanzil’ (bitter) and ‘Vlaspik’ (non-bitter) pickling cucumbers subjected to acidification or fermentation. Cucurbitacins C (CuC) and C-glycoside were putatively identified in ‘Hanzil’ cucumber fruits while undetectable in ‘Vlaspik’. The major cucurbitacin in ‘Hanzil’, CuC, increased in concentration with cucumber size, ranging from 28 ppm in size 2A to >74 ppm in size 4+ fruits. Endocarp had the highest CuC concentration (88.7 ± 44.3 ppm) followed by mesocarp (30.6 ± 15.1 ppm) and exocarp (2.58 ± 1.75 ppm). CuC was 3-fold lower in acidified cucumber (15.7 ± 10.3 ppm) and 10-fold less in fermented cucumber (4.90 ± 3.94 ppm) than when fresh (47.9 ± 22.8 ppm). Fermentation has potential for de-bittering of cucurbits, and oversized bitter cucumbers could serve as a source of CuC for exploration of bioactivities.