Detection of biosynthetic citric acid and sugar addition in Italian tomato passata using liquid chromatography–combustion–isotope ratio mass spectrometry

The citric acid is naturally present in tomatoes and can be added to tomato passatas (E330) with no restriction about its amount and origin. The additive E330 is mainly biosynthetically produced starting from the Aspergillus niger fed on cheap materials. For the first time, an isotopic method for the detection of biosynthetic citric acid addition to Italian tomato passata was provided. Italian tomato passata samples without added citric acid (287 samples) were analysed through LC-co-IRMS to establish reference values for tomatoes citric acid carbon isotopic ratio (δ¹³C_CA). The isotopic values of glucose (δ¹³C_G) and fructose (δ¹³C_F) have been considered to increase the method effectiveness and to be compared to the reference values provided by the AIJN (European Fruit Juice Association). The method showed good repeatability, with intra-day and inter-day standard deviations below 1.1 ‰ for citric acid, glucose, and fructose. The ratios between the isotopic values R_CA/G (δ¹³C_CA/δ¹³C_G) and R_CA/F (δ¹³C_CA/δ¹³C_F) were more effective in the detection of biosynthetic citric acid addition than the δ¹³C_CA alone.