The study, published in Plant Foods for Human Nutrition, report that the brown skin and external layers of ‘waste’ are rich in fibre and flavonoids, while discarded bulbs contain sulphurous compounds and fructans, which makes them useful sources of food ingredients that may be beneficial to health.
The authors, led by Vanesa Benítez from the Autonomous University of Madrid, Spain, said that the results of their study “showed that each waste would have a profit.”
“Industrial onion wastes …are an interesting source of phytochemicals and natural antioxidants and their application in food, which increases their health promoting properties, is a promising field,” said the authors.
“The results show that it would be useful to separate the different parts of onions produced during the industrial process,” explained Benítez.
“This would enable them to be used as a source of functional compounds to be added to other foodstuffs,” she added.
Industrial waste
According to Benítez and colleagues, onions (Allium cepa L.) are the second most important horticultural crop worldwide, after tomatoes, with current annual production around 66 million tonnes.
“Lately, there has been an increase in demand for processed onions which has led to an increase in waste production. Accordingly more than 500,000 tonnes of onion waste are produced annually in the European Union, mainly from Spain, UK and Holland,” they said.
Onion overage
The researchers said that the brown skin, top, and bottom of onion waste has potential for use as an ingredient rich in dietary fibre and in total phenolics and flavonoids, with high antioxidant activity.
“Moreover, brown skin showed a high concentration of quercetin aglycone and calcium, and top–bottom showed high concentration of magnesium, iron, zinc and manganese,” said Benítez and colleagues.
They added that the outer scales “could be used as source of flavonols, with good antioxidant activity and dietary fibre content”, noting that the scales provided a good ratio of soluble to insoluble fibre.
“Inner scales could be an interesting source of fructans,” they added.
Under-exploited
“It would be interesting that processors will separate the different parts of onion obtained during the onion processing due to their added value,” said the researchers, who noted that to date such the processing of waste products to add value has not been effectively exploited.
Benítez and colleagues added that the different functional compositions of the wastes suggest that industry should have a “great interest” in separating them to “exploit them as source of different bioactive compounds.”
“Moreover, if the recovery and the production of new products from the industrial onion wastes are successful … environmental problems could be solved,” they added.
Source: Plant Foods for Human Nutrition
Volume 66, Issue 1, Pages 48-57, doi: 10.1007/s11130-011-0212-x
“Characterization of Industrial Onion Wastes (Allium cepa L.): Dietary Fibre and Bioactive Compounds”
Authors: V. Benítez, E. Mollá, M.A. Martín-Cabrejas, Y. Aguilera, et al