Identification and quantification of quercetin glycosides present in different color onions (Allium cepa L.)

We identified and quantified quercetin 7, 4'-diglucoside (m/z 625), quercetin 3-glucoside (m/z 463), quercetin 4'-glucoside (m/z 463) and quercetin (m/z 301) using LC (ESI)-MS/MS and HPLC analysis. Quercetin glycosides contents varied amongst the different varieties of onion. The content of total quercetin glycosides was predominantly in first scaly leaves of all the varieties and drastically reduced. The total content of glycosides was mean 46.44 mg/g dry weight (DW), and quercetin 4'-glucoside was the predominant compound with mean 23.1 mg/g DW followed by quercetin 7,4'-diglucoside (11.20 mg/g DW) and quercetin 3-glucoside (3.68 mg/g DW) respectively. The highest quercetin content (32.81 mg/g DW) was found in first SL of chartreuse and second SL has higher quercetin content (9.88) than other cultivars. A distinct variation in the contents of quercetin glycosides was detected between the outer and inner layer. Thus, the variations of quercetin glycosides in the colorful onions were significant.