Identification and Quantification of Steroidal Alkaloids from Wild Tuber-Bearing Solanum Species by HPLC and LC-ESI-MS

Wild Solanum species are characterized by several types of glycoalkaloids (GAs), which are usually not found in commercial potato cultivars. These alkaloids serve as defence compounds against herbivores and microorganisms, especially fungi. In this study, the GA composition of tuber and leaf material of 17 wild Solanum species was analysed qualitatively by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) and quantitatively by high-performance liquid chromatography. The GAs identified were alpha-solanine, alpha-chaconine, beta-chaconine, solasonine, solamargine, demissine, dehydrodemissine, alpha-tomatine, dehydrotomatine, commersonine, dehydrocommersonine, leptine I and leptine II. Most species accumulated the common potato GAs alpha-solanine and alpha-chaconine in tubers and solasonine and solamargine additionally in leaves. In some species, such as S. acaule ssp. acaule, S. demissum and S. polyadenium, substantial amounts of unusual alkaloids were detected. By using LC-ESI-MS, we detected several minor alkaloids such as dehydrogenated forms of alpha-tomatine, demissine and commersonine for the first time. Total GA content, expressed as the sum of the four main alkaloids alpha-solanine, alpha-chaconine, solamargine and solasonine differed from species to species. In general, GA contents in leaf tissue were higher and GA patterns were more complex than those of tubers.