Random amplified polymorphic DNA (RAPD) fingerprint and antioxidants profile as markers for Tropea red onion (Allium cepa L.) authenticity

Random amplified polymorphic DNA (RAPD) and chemotype analyses were applied to characterise Tropea red onion (Allium cepa L.), a typical Italian variety that is cultivated in specific areas of Calabria. Seven Tropea red onion samples and three commercial cultivars of different coloured onions were evaluated. Amplification of genomic DNA using random primers highlighted a good clustering differentiating Tropea red onion cultivar from commercial reference samples used in this study. The total antioxidant activity and the content of quercetin-3,4′-O-diglucoside (3,4′Qdg) and quercetin-4′-O-monoglucoside (4′Qmg) were measured using photochemiluminescence method (Photochem®) and capillary electrophoresis, both very interesting because of their very short measuring times. The difference in antioxidant activity and quercetin contents between Tropea red onion and commercial sample and also the difference within Tropea cultivar suggested that the nutrient composition did not depend only on particular genetic characters but was probably connected to the intrinsic pedological soil and climate features.