Dry skin of the onion can be exploited

The production of onion waste has increased in recent years with the growing demand for these bulbs. In the EU generate over 500,000 tonnes of waste, especially in Spain, Netherlands and United Kingdom, which has become an environmental problem. The remains include dry skin brown, the outer layers, roots and stems, and onions which do not reach market size and who have suffered damage.

"One solution would be to use waste as a source of onion natural ingredients with high functional value, as this vegetable is rich in compounds that provide benefits to human health," points out to SINC Vanesa Benítez, researcher at the Department of Agricultural Chemistry at the Autonomous University of Madrid.

The research group belongs to Benitez, along with scientists from the University of Cranfield (UK) has identified in the laboratory substances and possible uses of each part of the onion. The results were published in the journal. Plant Foods for Human Nutrition.

According to the study, the brown skin could be used as a functional ingredient rich in dietary fiber (mainly insoluble type) and phenolic compounds, including quercetin and other flavonoids (plant metabolites with medicinal properties). The fleshy outer two layers of the onion also contain fiber and flavonoids.

"Consumption of fiber reduces the risk of cardiovascular disease, gastrointestinal diseases, colon cancer, type 2 diabetes and obesity," says the researcher.

For its part, the phenolic compounds help prevent heart disease and have anticancer activities. The high content of these compounds in dry skin and the layers outside the bulbs give them also a high antioxidant capacity.

As for internal parts and whole onions are discarded, the researchers propose to use them as a source of fructans and sulfur compounds. Fructans are prebiotics, ie, exert beneficial health effects by selectively stimulating the growth and activity of bacteria in the colon.

The sulfur compounds inhibit the aggregation of platelets, thus facilitating blood flow and, in general, improve cardiovascular health. In addition, positive change and anti-inflammatory antioxidant systems in mammals.

"The results indicate that it would be interesting to separate the different parts of the onion that is generated during industrial processing," said Benitez, "and so could be used as a source of functional compounds to be added to other foods."


Vanesa Benítez, Esperanza Molla, Mary A. Cabrejas Martin, Yolanda Aguilera, Francisco J. López-Andreu, Katherine Cools, Leon A. Terry, Rosa M. Stephen. "Characterization of Industrial Wastes Onion (Allium cepa L.): Dietary Fibre and Bioactive Compounds."Plant Foods for Human Nutrition 66 (1): 48-57, 2011.DOI: 10.1007/s11130-011-0212-x.

Source: SINC