Antiallergic activities of eleven onions (Allium cepa) were attributed to quercetin 4′-glucoside using QuEChERS method and Pearson's correlation coefficient

The antiallergic activity (type I hypersensitivity) of eleven onions (eight cultivars, three different geographical origins) used for daily meals was comparatively determined using RBL-2H3 cells. A large variation of antiallergic activity (IC50 = 20.8 to 310.1 µg/mL) was found in the edible parts. Among the eight cultivars, Satsuki showed the highest activity (IC50 = 89.1 µg/mL), and among the geographical origins Hokkaido was the most effective (20.8 µg/mL). The correlation coefficient between the antiallergic activities and thirty-four peaks in HPLC chromatograms of eleven onion extracts isolated using the QuEChERS method indicated that quercetin 4′-glucoside has a highly-positive correlation (r = 0.91) with the antiallergic activity. Indeed, quercetin 4′-glucoside was found in high concentration (140.1 mg/kg) in Hokkaido onions, and the isolated compound showed high antiallergic activity (IC50 = 3.0 µg/mL). Therefore, Hokkaido onions were the best inhibitors of type I allergy, possibly due to their high content of quercetin 4′-glucoside.