LC-ESI-FTICR MS/MS glycoalkaloid profiling and antibacterial activity of plant extracts from eggplant (Solanum melongena)

The discovery of bioactive components in foods is exciting, suggesting the possibility of improved public health through diet. However, the content of bioactive components in plant food depends upon both genetics and environment, including growing conditions, harvest and storage, processing and meal preparation. Glycoalkaloids (GAs) are nitrogen-containing molecules, composed by a steroidal moiety, called aglicone, and a sugar chain, usually three or four units, that are naturally produced in Solanaceae plant family 1. All these compounds have been detected in large amount in potato plant, such as α-solanine and α-chaconine, in tomato, such as α-tomatine and dehydrotomatine, and in Solanum melongena, popularly known as eggplant, such as solasonine and solamargine. Compounds belonging to this group appear to be largely unaffected by home processing conditions such as baking, boiling, frying and microwaving 2. Because GAs are reported to be involved in host-plant resistance and to have a variety of adverse as well as beneficial effects in cells, animals, and humans, there is the necessity to develop a clearer understanding of their roles both in the plant and in the diet 3. To contribute to this effort, in this work glycoalkaloids extracts obtained from eggplants were analysed by using an optimized high resolution LC-ESI-FTICR MS with tandem mass spectrometry (MS/MS) performed by infrared multiphoton dissociation (IRMPD). Moreover, the antibacterial activity and the minimal inhibitory concentration were evaluated against selected bacterial strains by using the agar well diffusion assay 4. A total of thirty-two Gram-negative and Gram-positive bacteria were employed as screening microorganisms for this study. Extracts showed an antibacterial effect on some Gram-negative and Gram-positive bacteria as well as the main pure components solamargine and solasonine, which were found active also when tested individually.