Chemical profile of common varieties of Allium cepa L. sold in FCT-Abuja, Nigeria

Onions (Allium cepa L.) belong to the family of vegetables and herbs with strong antioxidants properties that combats the formation of free radicals and other microbial based disease conditions. The study aimed at investigating chemical profile of common varieties of Allium cepa L. sold in FCT-Abuja, Nigeria. The samples were randomly purchased at point of sales, processed and analyzed for Phytochemical, antioxidant, mineral elements, microbial activities and GC-MS fingerprints using standard methods. Results indicated presence of alkaloid, flavonoids and tannin; antioxidant inhibitory concentrations (IC50) range of 1.496 - 2.961 mg/mL and presence of Ca, Mg, Cu, Cr and Fe were observed. The GC-MS fingerprints identified 17 compounds with retention times ranging from 3.09 to 9.77 minutes. The presence of flavonoids, alkaloids and tannins corroborated report from the earlier studies of white onions. Inhibitory concentrations of the antioxidants obtained are lower than values reported from previous similar studies. The levels of the mineral contents of all the samples are within the safe limits in terms of mineral overloads and contamination, while the GC-MS fingerprints indicated nine (9), eight (8) and seven (7) compounds in the red, white and brown varieties respectively. The allyl group from organosulfur compounds is responsible for the antimicrobial activities. All the varieties of Allium cepa L analyzed contained alkaloid, flavonoids, free from heavy metals contamination and also had potent antimicrobial activities due to the presence of the 17 compounds revealed by the GC-MS fingerprints which was not previously reported. The findings of the present study has therefore contributed to additional knowledge on the existing database on Nigerian cultivars of Allium cepa .