Chemical Investigations on some Constituents of Pigmented Onion Skins

An investigation on some constituents of the pigmented skins of two onion (Allium cepa) varieties, i.e. Feteel and Mokawar, was carried out. Differences were found between the two onion skina in their content of some components. The extraction conditions for obtaining maximum yields of pectic substances with ammonium oxalate as well as the characteristics of these substances were studied. The pectin of the Mokawar onion skins was found to be naturally low in methoxylated groups (4·27%) and contained arabinose, xylose, glucose, galactose and rhamnose as sugar components. That of the Feteel skins was relatively highly methoxylated (8·17%) and contained the same sugar components except for glucose. The partial acid hydrolysis of both pectins led to the formation of reductic acid and reductone.