Comparative analysis of volatile profiles and phenolic compounds of Four Southern Italian onion (Allium cepa L.) Landraces

Volatile and phenolic compounds of four onion landraces (Airola, Alifana, Montoro and Vatolla) cultivated in Campania region (southern Italy) were compared. Overall, 31 volatiles were identified in the four landraces including: sulfur metabolites (19), aldehydes (7), alcohols (2), acids (2) and others (3). Phenolic compounds, assigned using high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) and semi-quantified by HPLC coupled with a diode array detector, varied from 297.3 to 1348.3 mg/kg fresh onion. Principal Component Analysis performed on volatiles and phenolic compounds revealed a relatively high inter- and intra-landrace variability, since the relative concentration of individual volatile and phenolic components varied within ample ranges. The four landraces could be distinguished with sound confidence by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and chemometric analysis of the fresh bulb skin. The qualitative and semi-quantitative volatile profiles of Airola onions were distinct among each other, indicating sensorial peculiarity of this landrace. The presence of 2-methylfuran differentiated the five Vatolla samples, as the remaining landraces lacked it. Altogether, these results could support consumers' choices toward onion varieties with higher potential health benefits on a molecular basis and encourage future biodiversity programs to preserve onion landraces exhibiting valuable genetic resources.