Nitrogen Metabolism as a Tool to Discriminate Organic and Conventional Citrus Fruits

Background and methodology

This study aimed to develop a method for authenticity control of organically grown oranges. The study was conducted over a three-year period on oranges of Navelina and Tarocco cultivars, sampled from 28 farms (seven organic and seven conventional for each cultivar) from in the citrus area of eastern Sicily, Italy. Farms were chosen to obtain similar pairs in the same environmental conditions. The orchard pairs were homogeneous for age and rootstock to reduce effects not linked to fertilization. Oranges obtained from these production systems were differentiated through the detection of markers linked to nitrogen metabolism. In addition, total nitrogen (N) and synephrine contents in juice were determined. Each year of the study, samples of 80–100 fruits were harvested at commercial maturity from the organic and conventional managed farms.


The different production methods affected the levels of vitamin C in oranges of both varieties. The vitamin-C content of the organically grown fruits was higher than that of the conventional ones. Fruits from organically managed farms had statistically higher values compared to their conventional counterparts. Total nitrogen and synephrine contents were significantly higher in conventional fruits, whereas the nitrogen-isotope-ratio values were higher in organic fruits. This study concluded that by choosing some potentially discriminating variables, it is possible to classify a product of which the origin (be it organic or conventional) is unknown.


Rapisarda, P., Calabretta, M. L., Romano, G., & Intrigliolo, F. (2005). Nitrogen metabolism components as a tool to discriminate between organic and conventional citrus fruits. Journal of Agricultural and Food Chemistry, 53(7), 2664-2669. Available on-line at: