Onions are an important crop of the Allium family which also contain
high amounts of flavonols (quercetin) and phenolic compounds.
These not only vary according to cultivar but also within its layers. For
example, Nuutila et al. (2003) reported that the total phenolics of the
dry skin of red and yellow onions were 8000 and 2600 mg GAE/100 g
DW, respectively, whereas the intermediate levels of onion bulbs and
stems ranged from 80 to 320 mg of GAE/100 g DW. Shon, Choi, Kahng,
Nam, and Sung (2004) examined the total phenolic and flavonoid
content of onions cultivars (red, yellow and white). They noted that
both total phenolic and flavonoid content were high among red onions
compared to white and yellow onion cultivars.