posters 5th Asia-Pacific NMR Symposium 2013

NMR Spectroscopy Confirms the Absence of Solanidine Alkaloids in Solanum centrale J.M. Black Extract (#118)

Myrna A. Deseo 1 2 , Donald S. Thomas 3 , James M. Hook 3
  1. Southern Cross Plant Science, Southern Cross University, Lismore, NSW, Australia
  2. Cooperative Research Centre for Remote Economic Participation, Alice Springs, Northern Territory, Australia
  3. NMR Facility, Analytical Centre, University of New South Wales, Sydney, NSW, Australia

The fruit of Solanum centrale J.M. Black (Australian Bush Tomato) has long been a part of the tradition of the Indigenous people of Australia and being used as food. It has now found application in the food industry as condiments and one of the concerns to its commercialisation is the reported presence of solanidine alkaloid and its glycosides. The toxicity associated with these alkaloids impacts on food safety and thus, there is a need to develop a tool to confirm the presence or absence of the solanidines in Australian Bush Tomato. NMR spectroscopy is an accurate and a rapid tool that can be used for qualitative screening of solanidines.

The 1H and 13C NMR spectra of methanol extract fractions of S. centrale fruits (green, mature and dried) were compared with reference standards of solanidine, alpha-solanine and alpha-chaconine. The distinctive features of solanidines that are easily observed in 1H NMR spectrum are the vinylic proton at C5, the methyl singlets C18 and C19; and the methyl doublets (C21 and C27). Whilst a vinylic proton was observed in the 1H spectra of the extracts (5.4 ppm) the 13C chemical shifts of the methyl signals in the extract did not coincide with those of the solanidine standards. The chemical shifts of the methyl signals in the extracts were generally more upfield than the solanidine reference standards. Furthermore, HSQC confirmed the absence of geminally coupled protons (around 2.9 and 1.4 ppm) in the extracts that are directly correlated to a carbon at 60.6 ppm, which correspond to the protons at the C26 position that is vicinal to nitrogen in solanidines. The NMR spectral data suggested the presence of steroidal glycosides in the S. centrale extracts but not of the solanidine type.