Study On The Chemical Compositions And In Vitro Activities Of Aqueous Extracts From Liliaceae Storey Onion

Allium is rich in plant resources and widely distributed.It has a unique pungent smell and rich bioactive substances.It is a popular spice and vegetable,and also an important medicinal plant.Allium plants are rich in nutrients and bioactive substances,such as organosulfur compounds,steroids and flavonoids,which have antibacterial,antiplatelet aggregation,anticancer,antiviral,hypolipidemic,hypoglycemic and other pharmacological effects.Storey onion?Allium cepa L.var.proliferum Regel?is one of the varieties of onion.It is mainly distributed in the north of Shaanxi,Gansu,Ningxia and other places.Storey onion is a medicine food homologous plant,which is deeply loved by the local people.However,there are relatively few studies on the components and functions of storey onion.In this thesis,the chemical compositions and biological activities of storey onion were studied,comparing with onion and welsh onion.The general nutritional components of storey onion were analyzed and evaluated.The chemical compositions and relative contents of storey onion aqueous extract were determined by liquid chromatography-mass spectrometry.The antioxidant,antibacterial and anticancer activities in vitro of storey onion aqueous extract were studied.1. Analysis of general nutrients.The contents of protein,water,ash,crude fat,reducing sugar,total dietary fiber,vitamin?B₂,C,A,E?,amino acid,mineral element and soluble solid in fresh storey onion stem were determined.The results showed that the storey onion stem was rich in water,protein,reducing sugar,total dietary fiber,vitamin C,vitamin A and soluble solid.The content of total amino acids in the stem of storey onion is higher than that of welsh onion,and 25%of the total amino acids are essential amino acids,in which lysine and leucine are the higher contents,while aspartic acid,serine and glutamic acid are the higher contents of nonessential amino acids;storey onion is rich in mineral elements,in which K,Ca,Fe and Mg are relatively rich,while Zn,Cu and Mn are relatively low.2. Preparation of aqueous extracts and determination of total flavonoids and polyphenols.Three kinds of aqueous extracts from fresh storey onion,onion and welsh onion were obtained by ultrasonic extraction at 60°C 400 w for 30 min and vacuum distillation at 60°C.Among the three aqueous extracts of Alliums,the content of total flavonoids was the highest?0.99±0.06 mg RUE/g DW?in onion,the highest total polyphenols?11.34±0.22 mg GAE/g DW?in storey onion,and the welsh onion was the lowest.3. The composition and relative content of aqueous extracts.Using UPLC-ESI-MS/MS,42,37 and 38 compounds were identified from storey onion,onion and welsh onion in the positive and negative ion modes.The results showed that the main active substances in three extracts were organosulfur compounds,among which the content of organosulfur compounds in storey onion was the highest?962.20±34.55?g/g?,followed by onion?634.65±19.85?g/g?and welsh onion?606.48±22.92?g/g?;the contents of polyphenols?100.40±12.55?g/g?and organic acids?605.78±10.81?g/g?were the highest in storey onion,while alkaloids?71.96±4.34?g/g?and flavonoids?306.56±13.41?g/g?were the highest in onion.The compounds with highest content in storey onion was cycloalliin?551.74±8.12?g/g?,followed by ajoene?159.31±5.30?g/g?.The contents of ferulic acid?24.40±1.66?g/g?,rhamnazin?6.70±0.69?g/g?,leucopelargonin?7.76±1.58?g/g?and xanthopherol?25.75±3.64?g/g?in storey onion also were significantly higher than those in welsh onion and onion.4. Study on the antioxidant activity of aqueous extracts.Through the study of Fe³⁺reduction ability,ABTS free radical,OH^-free radical and DPPH free radical scavenging abilities,the antioxidant activities of storey onion,onion and welsh onion aqueous extracts were characterized in vitro.The results showed that the three kinds of Allium aqueous extracts had good antioxidant capacities.The antioxidant capacity of storey onion was the same as that of onion.The FRAP iron ion reducing power?absorbance value:0.32-2.21?,DPPH free radical scavenging ability(IC₅₀=1.24±0.52 mg/m L),OH^-free radical scavenging ability(IC₅₀=1.60±0.29 mg/m L)of storey onion were the strongest,and the ABTS free radical scavenging activity(IC₅₀=1.64±0.64 mg/m L)of onion was the strongest,while the extracts of welsh onion with the weakest antioxidant activities.5. Study on the antibacterial activity of aqueous extracts.Firstly,the inhibitory effects of storey onion,onion and welsh onion aqueous extracts on Bacillus cereus,Staphylococcus aureus,Acetobacter,Escherichia coli,Yeast and Aspergillus niger were evaluated by paper diffusion method,and the minimum inhibitory concentration?MIC?was determined by double dilution method.The results showed that the three aqueous extracts of Allium had a certain inhibitory effect on the six strains,which showed the broad-spectrum antibacterial activity of Allium extracts.For the six strains tested,the MIC value of storey onion aqueous extract were the lowest?MIC 31.3-125mg/m L?,showing the strongest antibacterial activity,followed by welsh onion aqueous extract,while the onion extract had the weakest antibacterial activity.6. Study on the anticancer activity of aqueous extracts.MTT method was used to determine the inhibitory rate of the aqueous extracts of storey onion,onion and welsh onion on the proliferation of Hep G2 cells,and flow cytometry was used to determine the rate of inducing apoptosis.The results showed that the three kinds of aqueous extracts of Allium had the ability of inhibiting the proliferation of liver cancer cells,and the inhibitory activity was concentration dependent,and the inhibitory rate increased with the prolongation of the action time between the extracts and the cancer cells;the aqueous extracts of storey onion had the strongest ability of inhibiting liver cancer cells(24 hours,IC₅₀=33.21±1.12 mg/m L),followed by welsh onion(24 hours,IC₅₀=73.26±1.19 mg/m L),while onion aqueous extract had the weakest anti-cancer ability(24 hours,IC₅₀=89.77±1.23 mg/m L).The results of apoptosis rate showed that three kinds of Allium could induce liver cancer Hep G2 cells apoptosis,among which storey onion had the strongest ability.