Use of high-resolution mass spectrometry for the first-time identification of gerberin as a tentative marker of the fraudulent organic production of tomatoes

Abstract

Solanum lycopersicum cv. Ramyle was cultivated using different amounts of synthetic and natural crop protection agents, combined with organic and chemical fertilisers. Chemometric studies on the LC-Q-Orbitrap metabolite profiles of tomatoes distinguished a compound [M+H]+ at m/z 291.1075 (C12H19O8+, 0.0 ppm). The compound, identified as gerberin, is a possible marker to distinguish between organic and conventional cultivation. To our knowledge, this is the first time gerberin has been identified in tomato. A combination of HRMS, in silico, and chemical experiments, allowed the structure elucidation. Target MS2 experiments of the 291.1075 peak showed a clear breakdown to a base peak at m/z 129.0546 Da, consistent with the gerberin aglycone proton adduct (C6H9O3). Acid hydrolysis of the extract showed the disappearance of all gerberin adducts remaining the 129.0546 ion only, which matched with a commercial standard of gerberin aglycone. The levels of gerberin in the samples correlated negatively with the presence of synthetic chemicals. Gerberin content variation correlated to the application of synthetic fertilisers (T1, T2, T3, and T4, from lowest to greatest application). δ15N IRMS measurements were insufficient to discern between agricultural practices, demonstrating that fraud in organic produce using synthetic fertilisers is possible if discrimination is based on IRMS only.