d18O as authenticity thresholds in differentiating tomato passata from diluted tomato paste

Tomato passata is one of the ‘pillars’ of the Mediterranean diet and is a typical Italian product that by law must be obtained exclusively from fresh tomatoes. For this reason Italian law provides for use of the 18O of vegetal water to determine whether passata (Brix of up to 12) is genuine or has been obtained by diluting tomato paste (Brix higher than 12). However, the same law gives no indication of reference limits for this parameter. In this study an extensive dataset of over 1000 samples were collected in different years (from 2004 to 2012) along the Italian tomato product production chain (tap waters, juices, passata, pastes). In all the samples collected the content of water d18O was investigated. This parameter was shown to be statistically different in the four classes of products, increasing from water to juice and paste, in relation to the different degree of evaporation taking place during the preparation phase. Moreover, the d18O of vegetal water, due to the contribution of the lower 18O values of tap water during dilution, was highly effective in distinguishing genuine passata from watered down paste, also in the case of passata previously concentrated up to 11.9 Brix. On the basis of these results two lower threshold values are proposed: -1.4‰ for ‘raw’ passata and -2.9‰ for passata previously concentrated up to 11.9 Brix.