The yellow onions of the market are able all to appear similar, but they are not all equal: more they are picked late, more their power antioxidant for the organism is big!
The yellow onions are especially rich in quercétine, an antioxidant of the family of the flavonoïdes. But some conditions exist susceptible to modify the concentration of it.
It is what Lars Mogren discovered, of the university of Sweden in sciences of agriculture (SLU). He/it stayed late to all stages of the culture of the yellow onion: the types and the quantities of fertilizing used, the types of cultivars, the moment of the harvest, the method of drying and the conditions of storage.
First observation: the content in quercétine of the onions home the same, that one uses the fertilizing organic (as manure) or inorganic (nitrogen). The quantity of fertilizing used dragged also no change. According to Lars Mogren, these observations should incite the agriculturists to reduce the use of it.
And no matter the types of cultivars: all yellow onions are worth themselves.
However, it is as he/it pushes that this vegetable becomes richer of antioxidants. So, the onions that Lars Mogren studied contained two times more of if they had been picked as the leaves were folded back to soil. Besides, more the field counts onions whose leaves are folded back, more the other onions will also be concentrated some, estimate the researcher.
Once drawn of soil, the onions are dried in the sun. The onions having benefitted in the sun from ten days of drying contained once and half more quercétine than those that one had just harvested, noticed the Swedish researcher.
For what is the temperature of storage, no difference between 1 °C and 8 °C. With regard to the length of storage either, even on several months.
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In the kitchen, it can be interesting to know that the outside layers of the onion are concentrated more in antioxidants that the center. In fact, the most distant layers in contain until ten times more that the core. A fact that also prevails for the red onion that, in addition to the quercétine, contains some Anthocyanins, of the antioxidants them also.
” But not the pain to keep the peripheral layers only, underline Lars Mogren. The whole onion contains, globally, sufficiently of to get the kindness of it long-term.
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