Extractability, stability, and accumulation of nepetoidins in Ocimum basilicum L. leaves and cell cultures

Abstract

Antioxidant polyphenols nepetoidin A and B are widely spread in Lamiaceae family yet often remain undetected due to their purported instability and poor extractability with polar solvents typically used for phenolics extraction. Coextraction of nepetoidins may confer additional, or enhance existing, bioactivities of polyphenol extracts. This study includes a detailed analysis of nepetoidin extractability from sweet basil (Ocimum basilicum L.) leaves, and a survey of their occurrence in basil tissue cultures and peltate trichomes. Coextraction of nepetoidins with the major polyphenol rosmarinic acid was possible with solvent mixtures, yet substantially less efficient than that with the respective preferred solvents. Nepetoidin, but not rosmarinic acid levels in extracts from dried leaves were dramatically reduced. However, this was not due to degradation suggested by earlier reports, but to reduced extractability, which could be restored by wetting the tissue with water prior to addition of nonpolar solvent. Nepetoidins were found to accumulate at high levels in basil callus and suspension cultures. Correlation analysis revealed three novel compounds that are coextracted with nepetoidins and are proposed to represent nepetoidin dimers. Candidate signals for nepetoidin and rosmarinic acid glycosides were also detected in dedifferentiated basil cells. By contrast, nepetoidins were not enriched in basil peltate trichomes. This study establishes optimized recovery procedure for nepetoidins, reports their production by dedifferentiated basil cells, and illustrates how sample preparation methodology affects the phytochemical findings. This study reports an improved method for the recovery of polyphenolic nepetoidins from fresh and dry plant tissue and demonstrates their high abundance in dedifferentiated Ocimum basilicum cells.