Development and validation of UHPLC-HRMS methodology for the determination of flavonoids, amino acids and organosulfur compounds in black onion, a novel derived product from fresh shallot onions (Allium cepa var. aggregatum)

Black onion, a new derived product from fresh onion, has been developed by processing (aging) fresh shallot onion in a temperature- and humidity-controlled room without using any artificial additives. The aim of this study was to adapt, optimize and validate two ultra-high-performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) methodologies for the determination of flavonoids, amino acids and organosulfur compounds in black onion. UHPLC-HRMS methods involving RP-C18 and HILIC columns were adapted and validated in terms of specificity, linearity, limit of detection (LD) and quantification (LQ), precision inter- and intra-day, recovery and matrix effect. Linearity ranged from 0.012 to 12.5 ngμL−1 and from 0.1 to 75 ngμL−1 for flavonoid and amino acids and organosulfur compounds, respectively. LD varied from 0.004 to 0.06 ngμL−1 and LQ from 0.012 to 0.2 ngμL−1. The intra-day and inter-day precision for all compounds were less than 15% and the recovery ranged from 69 to 106%. The matrix effect ranged from 80 to 114% for flavonoids, amino acids and organosulfur compounds. The described methods were successfully applied for the correct separation and determination of 53 compounds in black onion. These results establish the value of these new two UHPLC-HRMS protocols in providing detailed compound profiles of black onion, highlighting their potential applicability to similar vegetables.