δ15N has been used to distinguish organic from conventionally grown tomatoes for some time, but is not consistent. This paper describes an improvement on the δ15N SIRA method to authenticate organic tomatoes by undertaking the15N/14N analysis on the extracted amino acids. A gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) based method was developed, and analysis of C and N isotope ratios of amino acids taken along the passata production derived from tomatoes grown in two Italian regions over two years. δ15N was the most significant parameter for discriminating organic from conventional products, but the classification power was improved significantly by compound-specific (amino acids) isotope analysis regardless of the production years and regions.
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