الفهرس 
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Abstract
Phytochemical screening and antioxidant activities in different solvent extracts of onion were carried out. The extracts were subjected to various chemical tests for determination of phytochemical constituents.Total phenolic contents were evaluated using Folin Ciocalteu method and their antioxidant activity was assayed through «in vitro» radical scavenging activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH),Ferric reducing antioxidant power (ABTS) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid(FRAP assays,the phytochemical screening of this study indicated the presence of steroids, flavonoids, alkaloids, saponnins, and catechic tannins. The average total polyphenol content of hydroethanolic extracts was significantly (P<0.05) higher than in the hexane, ethyl acetate and dichloromethane extracts. The order of effectiveness half maximal inhibitory concentration (IC50) of the plant extracts as potent inhibitors was hydroethanolic extract, followed by Dichloromethane, ethyl acetate while the least was the hexane extract, When using (DPPH, ABTS and FRAP assays). This shows that onion organic solvent extracts especially the hydroethanolic extracts may be a potent source of natural antioxidants and can be used in the management of diseases associated with oxidative stress. The extracts were tested for their antibacterial activities against Gram-positive bacteria
(B. subtilis) and Gram-negative bacteria (Serratia marcescens). The preparation conditions of onion polysaccharide-iron complex (OPs-Fe) were optimized and the physicochemical properties were characterized by Ultraviolet-visible spectroscopy (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM), Thermogravimetric analyzer, and Differential scanning calorimetry (TGA-DSC), respectively. The stability and reducibility of OPS and OPS-Fe were analyzed, and the monosaccharides composition was determined by High performance liquid chromatography (HPLC). In-vitro antioxidant activity of OPS and OPS-Fe were evaluated by determining the radical (DPPH and hydroxyl radical) scavenging abilities. The results showed that the highest iron content of OPS-Fe (15.61% ±0.04) was obtained at the optimum conditions: reaction temperature was 38.0°C, reaction time was 3.0 h, FeCl3 addition was 2.9 mL and pH was 9. OPS-Fe formed a complex with β-FeOOH as the core and polysaccharides on its surface,and it was stable at pH 3 " ~ " 14. HPLC showed that the major monosaccharides were mannose (Man) and galactose (Gal) with a ratio of 1:5.15. Invitro free radical scavenging activity of OPS-Fe was signifcantly (P< 0.05) better than OPS. The IC50 of OPS-Fe against DPPH and hydroxyl radical were 3.785 mg/mL and 1.460 mg/mL, respectively.