GC-MS Investigation of Essential oil and antioxidant activity of Egyptian White Onion ( Allium cepa L . )

Objectives: This study carried out to investigate the chemical constituents of white onion (Allium cepa L.) essential oil as well as evaluate the antioxidant activities, total phenolic and total flavonoid contents of their different extracts. Methods: The Essential oil of white onion (Allium cepa L.) bulbs were extracted by hydro distillation method and analysed by gas chromatography coupled with mass spectrometry (GC–MS) to determine the chemical composition of the volatile compounds. The antioxidant activities of the methanolic extract of white onion and its derived fractions (n-butanol and water fractions) were determined by using two different spectrophotometric techniques as DPPH (2, 2-diphenyl-1-picrylhydrazyl radical) scavenging assay and phosphomolybdenum assay. Also, the total phenolic and flavonoid contents were determined. Results: In total, GC-MS analysis showed 40 compounds representing 93.89 % of the total oil composition were identified. The major compound in this essential oil was dodecane (28.69 %) and the other predominant constituents were represented 65.20% contains hydrocarbons, alkaloids and organosulfur compounds. The antioxidant results showed that the butanolic fraction has the highest antioxidant activity in the DPPH assay (SC50 = 59.21 ± 0.35 μg/ml) and phosphomolybdnum assay (127.92 ± 1.00 mg ascorbic acid eq. /g ext.). Also, the butanolic fraction has high total phenolic (41.05± 0.34 mg gallic acid eq. /g ext.) and flavonoid contents (3.82± 0.24 (mg rutin eq. /g ext.). Conclusion: The essential oil content and the antioxidant results of white onion (Allium cepa L.) may be have great potential for their application in food preservation and natural health products.