Onion Waste Contain Healthful Compounds

Onion waste, including the dry brown skin, the outer layers, roots and stalks, are rich in compounds that are beneficial for human health, according to new research published in the journal Plant Foods for Human Nutrition. The findings may lead to food waste that could be used as food ingredients.


Researchers at the Autonomous University of Madrid and Cranston University said the brown skin and external layers are rich in fiber and flavonoids, while the discarded bulbs contain sulphurous compounds and fructans.

"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", the researchers said. "The results show that it would be useful to separate the different parts of onions produced during the industrial process. This would enable them to be used as a source of functional compounds to be added to other foodstuffs."

The researchers conducted lab experiments to identify the substances and possible uses of each part of the onion. According to the study, the brown skin could be used as a functional ingredient high in dietary fiber (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 fiber and flavonoids.
"Eating fiber reduces the risk of suffering from cardiovascular disease, gastrointestinal complaints, colon cancer, type 2 diabetes and obesity", they said.

Phenolic compounds help prevent coronary disease and have anti-carcinogenic properties. The high levels of these compounds in the dry skin and the outer layers of the bulbs also give them high antioxidant capacity.

They also suggested using the internal parts and whole onions that are thrown away as a source of fructans and sulphurous compounds. Fructans are prebiotics that stimulate the growth and activity of bacteria in the colon. Sulphurous compounds reduce the accumulation of platelets, improving blood flow and cardiovascular health.