Bulk and compound-specific stable isotope ratio analysis for authenticity testing of organically grown tomatoes.

Until now, there has been a lack of analytical methods that can reliably verify the authenticity of organically grown plants and derived organic food products. In this study, stable isotope ratio analysis of hydrogen (H, δH), carbon (C, δC), nitrogen (N, δN), oxygen (O, δO) and sulfur (S, δS) was conducted along the tomato passata production process using organic and conventionally grown tomatoes from two Italian regions over two years. A gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) based method was developed and applied for analysis of C and N isotope ratios in amino acids derived from tomatoes. Of the bulk isotope ratios, δN was the most significant parameter for discriminating organic from conventional products. The classification power was improved significantly by compound-specific isotope analysis regardless of the production years and regions. We conclude that isotope analysis of amino acids is a novel analytical tool for complementing existing certification and control procedures in the organic tomato sector.