New markers for the traceability of organic fruit

The objective of the present research was to define a traceability system for organic fruits (orange, peach and strawberry) to monitor the classical parameters of quality (carpometric characteristics, total soluble solids (TSS), total acidity (TA), and ascorbic acid). We also aimed to monitor the parameters of several plant metabolites, such as synephrine in orange juice, ellagic acid in strawberries, and phenolic and volatile compounds in peaches, whose biosynthesis could be influenced by the use of an organic or conventional cultivation system. In addition, taking into account several specific aspects of the two cultivation methods, such as the different kinds of nitrogen soil fertilization used, a study was carried out to verify the possibility to differentiate between organically and conventionally grown fruit through the detection of markers linked to nitrogen metabolism. The ratio of stable isotopes of nitrogen 15N/14N in the proteins of pulp (delta15N PP) of different fruit species was determined. Our results showed that the cultivation method did not determine relevant differences in the quality parameters in oranges and peaches, whereas in strawberries, differences between organic and conventional fruits were observed. The ascorbic acid content in the three species studied was always higher in the organic fruits. Moreover, the level of bioactive compounds, such as skin anthocyanins in the ‘Spring Lady’ peach cultivar, was higher in the organically grown fruits. Peaches and oranges from organically managed farms had statistically higher delta15N PP values compared with the conventional ones. Therefore, the application of organic fertilizers, which notoriously increase the level of delta15N in the soil, also leads to an increase of delta15N values in the organic fruit. For that reason, this parameter can be used as a new marker to differentiate organically from conventionally grown fruit. Regarding the delta15N level found in strawberry pulp, no difference was observed between organic and conventional fruits because organic fertilizers are often employed even in conventional systems.