Thrown Away Dry Onion Skin are Rich in Fibre and Flavonoid

The brown skin and external layers of onion which are thrown away as waste are rich in fibre and flavonoids, while the discarded bulbs contain sulphurous compounds and fructans. Scientists say that all of these substances are beneficial to health.
 Production of onion waste has risen over recent years in line with the growing demand for these bulbs. More than 500,000 tonnes of waste are generated in the European Union each year, above all in Spain, Holland and the United Kingdom, where it has become an environmental problem. The waste includes the dry brown skin, the outer layers, roots and stalks, as well as onions that are not big enough to be of commercial use, or onions that are damaged. 
"One solution could be to use onion waste as a natural source of ingredients with high functional value, because this vegetable  is rich in compounds that provide benefits for human health", Vanesa Benítez, a researcher at the Department of Agricultural Chemistry at the Autonomous University of Madrid (Spain), tells SINC.
Benítez's research group worked with scientists from Cranfield University (United Kingdom) to carry out laboratory experiments to identify the substances and possible uses of each part of the onion. The results have been published in the journal Plant Foods for Human Nutrition.
According to the study, the brown skin could be used as a functional ingredient high in dietary fibre (principally the non-soluble type) and phenolic compounds, such as quercetin and other flavonoids (plant metabolites with medicinal properties). The two outer fleshy layers of the onion also contain fibre and flavonoids.