Determination of antioxidant capacity and flavonoid composition of onion (Allium cepa L.) landrace 'Krishnapuram' bulb using HPLC-ESI-ITMS

This study reports for the first-time antioxidant activity and flavonoid composition of KP onion landrace which is useful for future breeding programs and to obtain geographical indication (GI) tag for the benefit of farmers. The present study was aimed to determine antioxidant capacity and flavonoid composition of bulbs of red onion (Allium cepa L.) landrace 'Krishnapuram' (KP) from India using high-performance liquid chromatography (HPLC)-Electrospray Ionization (ESI)-multistage Ion Trap Mass Spectrometry (ITMS). The antioxidant activity was assayed by Ferric Reducing Antioxidant Power (FRAP) and hypochlorous acid (HClO)-induced oxidative damage in human erythrocytes. The total phenolic (TPC) contents in KP onion bulb extract (with 80% methanol) found to be 1.10 ± 0.2 mg GAE/g FW and 38.88 ± 1.0 µM QE/g. The FRAP activity measured for the bulb extract was 13.20 ± 0.1 µM QE/g. KP onion bulb extracts protected red blood cells (RBC) effectively (23%) against the oxidative damage induced by HClO. HPLC-ESI-ITMS analysis showed the presence of eight flavonols and five anthocyanins. Quercetin 3,4?-O-diglucoside (384.71 ± 0.49 mg/kg FW) and cyanidin 3-(6??-malonylglucoside) (20.95 ± 0.60 mg/kg FW) were detected as major flavonol and anthocyanin, respectively. The study suggests that KP onion has a considerable antioxidant activity due to the presence of high TPC. Moreover, quercetin glucosides are found to be more abundant than quercetin. The differences in quercetin glycosides content among different red onions could be useful for breeding programmes in the future.