January 14/Medicine & Law Weekly -- "Onions are excellent sources of bioactive compounds including fructo-oligosaccharides (FOS) and polyphenols. An onion by-product was characterized in order to be developed as a potentially bioactive food ingredient," investigators in Frederiksberg, Denmark, report.

"Our main aim was to investigate whether the potential health and safety effects of this onion by-product were shared by either of two derived fractions, an extract containing the onion FOS and polyphenols and a residue fraction containing mainly cell wall materials. We report here on the effects of feeding these products on markets of potential toxicity, protective enzymes and gut environment in healthy rats.

"Rats were fed during four weeks with a diet containing the products or a control feed balanced in carbohydrate. The onion by-product and the extract caused anaemia as expected in rodents for Allium products. No other toxicity was observed, including genotoxicity. Glutathione reductase (GR) and glutathione peroxidase (GPx 1) activities in erythrocytes increased when rats were fed with the onion extract. Hepatic gene expression of Gr, Gpx1, catalase, 5-aminolevulinate synthase and NAD(P)H:qui none oxidoreductase was not altered in any group of the onion fed rats. By contrast, gamma-glutamate cysteine ligase catalytic subunit gene expression was upregulated but only in rats given the onion residue. The onion by-products as well as the soluble and insoluble fractions had prebiotic effects as evidenced by decreased pH, increased butyrate production and altered gut microbiota enzyme activities," wrote E. Roldanmarin and colleagues, University of Copenhagen.

The researchers concluded, "The onion by-products have no in vivo genotoxicity, may support in vivo antioxidative defence and alter the functionality of the rat gut microbiota."

Roldanmarin and colleagues published their study in British Journal of Nutrition ("Effects of an Onion By-product on Bioactivity and Safety Markers in Healthy Rats." British Journal of Nutrition, 2009;102(11):1574-1582).

For additional information, contact L.O. Dragsted, University of Copenhagen, Dept. of Human Nutrition, 30 Rolighedsvej, DK-1958 Frederiksberg, Denmark.

From the January 18, 2010, Prepared Foods E-dition