Isolation and identification of components of mother liquor sugar from Stevia rebaudiana Bertoni with nematicidal activity

Mother liquor sugar (MLS) is a highly prevalent by-product of processing Stevia rebaudiana Bertoni, which is an important cash crop used to prepare a natural sweetener. With an increase in demand for stevia, MLS production has also increased. However, MLS has limited applications owing to its complex sweetness profile and pronounced bitter aftertaste. To explore the potential reuse of MLS, two diterpenoid compounds were gradually separated and identified using polarity-based separation, normal-phase chromatography, reversed-phase chromatography and LH-20 separation followed by an acute toxicity tracking test in Caenorhabditis elegans. These compounds were identified as sterebins E and F using high-performance liquid chromatography, mass spectrometry and nuclear magnetic resonance. Sterebins E and F were found to be isomers, and sterebin F exhibited stronger nematicidal activity than sterebin E and fosthiazate at 24 h. The preliminary isolation of sterebin F was achieved via gradient elution using macroporous HPD-100 resin with methanol concentrations of 70 %, 90 % and 100 %. The adsorption process lasted approximately 10 h, and the desorption process was completed in 2 h. To the best of our knowledge, this is the first study to identify specific individual compounds from stevia by tracking their nematicidal activity. The insights gained into the nematicidal properties and isolation process of sterebin F from MLS provide a crucial theoretical and practical foundation for developing eco-friendly pest control solutions and natural alternatives to chemical pesticides in sustainable agriculture.