Dry onion skin has a use

July 14, 2011
Dry onion skin has a use
The brown skin and external layers of the onions are rich in fiber and flavonoids. Credit: SINC

More than 500,000 tonnes of onion waste are thrown away in the European Union each year. However, scientists say this could have a use as food ingredients. The brown skin and external layers are rich in fibre and flavonoids, while the discarded bulbs contain sulphurous compounds and fructans. 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 each year, above all in Spain, Holland and the United Kingdom, where it has become an . 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 that provide benefits for ", 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 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 (principally the non-soluble type) and phenolic compounds, such as quercetin and other (plant metabolites with medicinal properties). The two outer fleshy layers of the also contain fibre and flavonoids.

"Eating fibre reduces the risk of suffering from cardiovascular disease, gastrointestinal complaints, colon cancer, type-2 diabetes and obesity", the researcher points out.

Phenolic compounds, meanwhile, help to 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.

Meanwhile, the researchers suggest using the internal parts and whole onions that are thrown away as a source of fructans and sulphurous compounds. Fructans are prebiotics, in other words they have beneficial health effects as they selectively stimulate the growth and activity of bacteria in the colon.

Sulphurous compounds reduce the accumulation of platelets, improving blood flow and cardiovascular health in general. They also have a positive effect on antioxidant and anti-inflammatory systems in mammals.

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

Related Stories

Recommended for you

Anti-cancer chemotherapeutic agent inhibits glioblastoma growth and radiation resistance

July 24, 2017
Glioblastoma is a primary brain tumor with dismal survival rates, even after treatment with surgery, chemotherapy and radiation. A small subpopulation of tumor cells—glioma stem cells—is responsible for glioblastoma's ...

New therapeutic approach for difficult-to-treat subtype of ovarian cancer identified

July 24, 2017
A potential new therapeutic strategy for a difficult-to-treat form of ovarian cancer has been discovered by Wistar scientists. The findings were published online in Nature Cell Biology.

Immune cells the missing ingredient in new bladder cancer treatment

July 24, 2017
New research offers a possible explanation for why a new type of cancer treatment hasn't been working as expected against bladder cancer.

No dye: Cancer patients' gray hair darkened on immune drugs

July 21, 2017
Cancer patients' gray hair unexpectedly turned youthfully dark while taking novel drugs, and it has doctors scratching their heads.

Shooting the achilles heel of nervous system cancers

July 20, 2017
Virtually all cancer treatments used today also damage normal cells, causing the toxic side effects associated with cancer treatment. A cooperative research team led by researchers at Dartmouth's Norris Cotton Cancer Center ...

Molecular changes with age in normal breast tissue are linked to cancer-related changes

July 20, 2017
Several known factors are associated with a higher risk of breast cancer including increasing age, being overweight after menopause, alcohol intake, and family history. However, the underlying biologic mechanisms through ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.