Onion skin waste ups antioxidant activity in bread, finds study

A study published in the journal Food Chemistry​ by Gawlik-Dziki et al. ​found that dried and ground onion skins could be used at 3% levels to replace wheat flour, upping the presence of quertin, an antioxidant which guards against cell damage and has anti-inflammatory properties.

By-product to create functional bread​

“Onion has been shown to be one of the main sources of dietary flavonoids in many countries​,” said the study. “Regardless of their high levels of flavonoids, a large amount of onion skin remains unused after onion processing."​

The researchers found that onion skin could increase the presence of quertin in bread, which help those developing countries where wheat flour accounts for 50% of the total energy intake.

Preparing the skins​

To reach their conclusions, they washed dried onion skin with deionized water and dried the skins further in an oven at 50°C before grinding the material to a powder.

They replaced wheat flour in bread formulations with dry onion skin powder at 1-5% levels and compared with a control that contained no dry onion skin.

Onion skin is known to contain higher flavonoid levels than the onion itself, according to earlier research.

Researchers in the present study found that formulations with more onion skin exhibited higher antioxidant activity despite being subject to high temperatures in the bread making process.

Consumer acceptability​

A sensory panel of sixteen 24-45 year olds tested the samples to measure consumer acceptability.

They deemed breads with up to 3% onion skin replacement acceptable, while higher levels were found to cause a sharp aroma and taste.

The crust and crumb of the enriched breads were much darker than the control, but this had no negative influence on the panel.

No organic solvents​

The researchers said this study differed to previous research into onion skins which used organic compounds such as ethanol to extract antioxidants.

The authors of this study said their method was “cheaper, easier to produce and safer for consumers”.​

They added that extraction using ethanol was not possible in bread production as it would interfere with yeast action.

Source:​​
Food Chemistry, Vol. 138, Issues 2–3, 15 May–1 June 2013, pps 1621–1628
http://dx.doi.org/10.1016/j.foodchem.2012.09.151​
‘Quality and antioxidant properties of breads enriched with dry onion (Allium cepa L.) skin’​
Authors: Urszula Gawlik-Dzikia, Michał Świecaa, Dariusz Dzikib, Barbara Baraniaka, Justyna Tomiłob, Jarosław Czyżc