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Analysis of the phytochemical contents and antioxidant activities of crude extracts fromTulbaghia species

更新时间:2016-07-05

INTRODUCTION

The human body has complex antioxidant defense systems that use antioxidant enzymes(e.g.,glutathione peroxidase,superoxide dismutase,and catalase)and non-enzymatic antioxidants(e.g.,glutathione,vitamins E and C,thiol antioxidants,melatonin,and carotenoids).Almost all organisms possess antioxidant and repair systems to protect themselves against oxidative damage,but these systems cannot completely prevent damage.1-3This deficiency may result in oxidative stress.

Oxidative stress caused by free radicals is related to the development of multiple diseases in which inflammation plays an important role,such as cardiovascular disease,rheumatoid arthritis,asthma,chronic obstructive pulmonary disease,neurodegenerative and autoimmune diseases,and some cancers.4-6Free radicals can stimulate or sustain inflammatory processes and their neutralization by antioxidants can prevent inflammation.Synthetic antioxidants that are currently on the market,such as butylated hydroxyl anisole,butylated hydroxyl toluene,tertiary butylated hydroquinone,and gallic acid esters,reportedly cause several side effects.1

where Acontrol is the absorbance of the control(DPPH solution without any sample)and Atest is the absorbance of the test sample(DPPH solution plus the sample).The inhibitory concentration(IC50)value is the concentration of the sample that is required to scavenge 50%of the DPPH free radicals.

The genus Tulbaghia(Amaryllidaceae family)contains approximately 30 species of mostly rhizomatous plants found in southern Africa.Tulbaghia are found in southern Tanzania,Malawi,Botswana,Zimbabwe,Mozambique,Lesotho,and South Africa.In South Africa,the majority of species are endemic to the Eastern Cape,Gauteng,KwaZulu-Natal,Limpopo,and Mpumalanga provinces.11,12Tulbaghia violacea is the most popular member in the genus and is commonly known as wild/sweet/society garlic,pink agapanthus,wilde knoffel(Afrikaans),itswele lomlambo(Xhosa),mothebe(Sotho),and isihaqa(Zulu).10Tulbaghia are used in traditional medicine for the treatment of numerous ailments,including fits,paralysis,headaches,high blood pressure,fevers,rheumatism,heart problems,chest complaints,stomach ailments,constipation,andcolic.11,13-16They are also used to treat various microbial infections,including oral,ear,and pulmonary infections.11,17,18

The aim of this study was to evaluate the phytochemical and total phenolic acid contents,and the antioxidant activities of selected Tulbaghia species.

MATERIALS AND METHODS

Plant material

Eight Tulbaghia samples were obtained from different indigenous plant nurseries in Gauteng,South Africa in May 2015.The plants were kept in a greenhouse at Vaal University of Technology,Vanderbijlpark,South Africa.The herbarium samples were authenticated by a botanist,ProfessorStefanSeibertatNorthWestUniversity(Potchefstroom,South Africa)where Voucher specimens were deposited in the AP Goossens Herbarium.

Preparation of plant powder material and acetone crude extracts

Fresh plant material was freeze dried and then ground into a fine powder.The powdered material was stored in airtight bottles at 4℃until required.To prepare crude extracts of the samples,10 g of fresh leaves from each sample was homogenized in 100 mL of absolute acetone.The homogenate from each plant was allowed to stand for 24 h and then filtered through No.1 Whatman filter paper.The acetone from each filtrate was evaporated in a fume hood and the extract was kept at 4℃until required for analysis.

Phytochemical screening

Phytochemical constituents of the Tulbaghia leaf extracts were determined according to standard methods.Alkaloids:each powdered leaf sample(0.5 g)was stirred in 5 mL of 1%aqueous hydrochloric acid in a water bath at 65℃.The solution was filtered using a No.1 Whatman filter paper and the filtrate was divided into two portions.Aliquots(1 mL)of the first and second portions were treated with a few drops of Mayer's reagent and Drangendorff's reagent,respectively.Turbidity or precipitation with either of those reagents was taken as preliminary evidence of the presence of alkaloids in the extract.

Tannins:a 0.5-g portion of each powdered sample was boiled in 20 mL of water in a test tube and then filtered through a No.1 Whatman filter paper.A few drops of 0.1%ferric chloride was added to the filtrate and a brownish-green or blue-black coloration was taken as evidence of the presence of tannins.

Phlobatannins:a 0.5-g portion of each powdered sample was extracted into 10 mL of distilled water and then filtered through a No.1 Whatman filter paper.An aliquot(4 mL)of the filtrate was boiled with 1%aqueous hydrochloric acid and observed for deposition of red precipitate,which was taken as evidence of the presence of phlobatannins.

Saponins:approximately 2 g of each powdered sample was boiled in 20 mL of distilled water in a water bath and then filtered through a No.1 Whatman filter paper.An aliquot(10 mL)of the filtrate was mixed with 5 mL of distilled water,shaken vigorously,and observed for formation of a stable froth.Three drops of olive oil were then added to the sample,shaken vigorously again,and then observed for the formation of an emulsion,which indicated that saponins were present.Steroids:acetic anhydride(2 mL)was added to a 0.5 g of acetone crude extract(Section 2.2)with 2 mL of sulfuric acid.A color change from violet to blue or green indicated steroids were present.

Terpenoids(Salkowski test):five milliliters of each extract of 100 mg/mL(Section 2.2)as mixed with 2 mL of chloroform,and then 3 mL of sulfuric acid was carefully added to form a layer.A reddish-brown coloration at the interface indicated terpenoids were present.Cardiac glycosides(Keller-Killani test):five milliliters of each extract(Section 2.2)was treated with 2 mL of glacial acetic acid containing one drop of ferric chloride solution.Then,a layer of 1 mL of concentrated H2SO4was added.A brown ring at the interface indi-cated that glycosides were present.

Flavonoids:each powder(1 g)was heated in 10 mL of ethyl acetate in a water bath for 3 min.The mixture was filtered through a No.1 Whatman filter paper,and 4 mL of the filtrate was shaken with 1 mL of dilute ammonia solution.Development of a yellow-green color indicated flavonoids were present.

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Quantitative phytochemical screening

Total phenolic acid content:the total phenolic acid contents of the acetone extracts(Section 2.2)were determined using the Folin-Ciocalteu reagent.19Aliquots(0.5 mL)of the dilute acetone extracts(1 mg/mL)and gallic acid(standard)were mixed with Folin-Ciocalteu reagent(5 mL,1∶10 diluted with distilled water)and aqueous sodium carbonate(4 mL,1M).The mixture was allowed to stand for 15 min and total phenolic acid content was determined spectrophotometrically at 760 nm.A standard curve was prepared using 0,50,100,150,200,and 250 mg/L solutions of gallic acid in methanol:water(50∶50,v/v).The total phenolic acid contents are expressed in milligrams of gallic acid equivalents per gram of fresh material.20

Total flavonoid content:the aluminum chloride colorimetric method21was used to determine the flavonoid content.Acetone extracts(Section 2.2)(0.5 mL,0.1 mg/mL)were diluted with acetone to 2 mL and then mixed with 0.5 mL of aluminum chloride(1.2%w/v)and 0.5 mL potassium acetate(120 mM).The mixtures were allowed to stand for 30 min at room temperature and then the absorbance was measured at 415 nm.Quercetin was used as a standard.The flavonoid content is expressed in milligrams of quercetin equivalents per gram of fresh material(mg QE/g).22

Antioxidant activity

Analysis of extracts by Thin Layer Chromatography(TLC):TLC plates(silica gel 60 F254plates,Merck KGaA,Darmstadt,Germany)were prepared using aliquots(4 μL)of the 100 mg/mL acetone extracts(Section 2.2).A mixture of benzene,ethanol,and ammonium hydroxide was used as the separating solvent in a total volume ratio of 36∶4∶0.4,respectively.One TLC plate was sprayed with freshly prepared vanillin reagent(0.1 g of vanillin,28 mL of methanol,and 1mL of sulfuric acid)to visualize the separated compounds,and then heated at 110℃for color development.The second TLC plate was sprayed with a solution of 1,1-diphenyl-2-picrylhydrazyl(DPPH)to determine the antioxidant activities.This plate was allowed to stand for approximately 5 min and the color change was noted.Compounds with the ability to scavenge radicals and reduce the DPPH caused a color change from deep purple to pale yellow.

1,1-diphenyl-2-picrylhydrazyl(DPPH)assay:aliquots(1 mL)of the extracts(Section 2.2)with concentration ranging from 0.01 to 5 mg/mL,were mixed with 1 mL of a 0.12 mM DPPH solution.After shaking,the mixture was incubated at ambient temperature in the dark for 30 min,and then the absorbance was measured at 517 nm using a UV-160U spectrometer(PG instruments,Leicestershire,UK).Acetone was used as a negative control and L-ascorbic acid was used as a positive control.The radical scavenging activity was determined as the percentage of inhibition using the following equation:

%scavenging activity=[(Acontrol-Atest)/Acontrol´100

Medicinal Plants contain a wide variety of phytochemicals,such as flavonoids,anthocyanins,carotenoids,dietary glutathione,vitamins,and endogenous metabolites that can have high antioxidant activities.Therefore,current investigations are directed towards naturally occurring bioactive compounds from sources such as plants.7Plant phytochemicals act against free radical induced oxidative stress and do not have the side effects of synthetic antioxidants.1,8The compounds that are responsible for reducing cellular oxidative stress could be isolated from plant extracts and then used for development of drugs for the prevention and treatment of many human diseases.Plant-derived antioxidants can function as singlet and triplet oxygen quenchers,peroxide decomposers,enzyme inhibitors,and synergists.9

胰腺癌免疫治疗有3个主要障碍会影响其疗效。首先,胰腺癌的突变负荷相比黑色素瘤和肺癌较低[23-24]。其次,胰腺癌很大程度上表现为免疫抑制,特征上表现为致密结缔组织增生反应,伴有明显的致瘤性巨噬细胞和骨髓来源的抑制性细胞(MDSCs)浸润[25]。第三,胰腺癌微环境中T细胞浸润较少,因此不能提供足够的T细胞反应。胰腺癌产生的非免疫原性肿瘤微环境限制了免疫检查点抑制剂的活性。因此,通过一些联合治疗方法(表1),可能使“冷”肿瘤微环境转变为“热”肿瘤微环境,从而提高免疫检查点抑制剂的临床疗效。

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2,2′-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid(ABTS)assay:the acetone plant extracts(Section 2.2)were prepared in acetone with concentrations ranging from 0.01 mg/mL to 0.5 mg/mL.L-Ascorbic acid was used as a positive control and acetone was used as a negative control.A 7-mM stock solution of ABTS was prepared in double-distilled water.The ABTS radical cation was then prepared by adding 88 μL of 140 mM potassium persulfate to 5 mL of ABTS.This solution was stored in the dark for 12-16 h to stabilize it before use.Shortly before conducting the assay,the concentrated ABTS+solution was placed in a cuvette and diluted with cold ethanol to a final absorbance of 0.70±0.02 at 734 nm and 37℃.The total scavenging capacitiesoftheextractswerequantifiedbyadditionof1000 μL of ABTS+to 50 μL of each plant extract.The solutions were heated on a heating block at 37℃for 4 min,after which the absorbance at 734 nm was recorded using a spectrophotometer.23All assays were performed in triplicate.

Statistical analysis

1 Subedi L,Timalsena S,Duwadi P,Thapa R,Paudel A,Parajuli K.Antioxidant activity and phenol and flavonoid contents of eight medicinal plants from Western Nepal.J Trad Chin Med 2014;34(5):584-590.

RESULTS

Preliminary phytochemical analysis

Preliminary phytochemical analysis of the eight Tulbaghia species showed the presence of flavonoids,glycosides,tannins,terpenoids,saponins,and steroids(Table 1).

当前,由于本体自身的复杂性,本体的全自动化构建还无法完全实现,在具体应用领域,本体的构建还需要专家的人工参与,为了减少建模过程中繁琐的人工操作,就必须借助本体构建(工具)软件完成某些半自动的构建过程。截止到2004年,已有的本体构建工具共有96种,包括了本体的合并工具、本体的评价工具、本体的标引工具、本体的集成工具等 [11-12]。

Total phenolic acid and flavonoid contents

The total phenolic acid contents in the different plant extracts ranged from 4.50 to 11.10 mg of gallic acid equivalents per gram of fresh material.The total phenolic acid contents of the different extracts were not significantly different(P>0.05),except for Tulbaghia vio-lacea.Tulbaghia violacea had a significantly higher(P<0.05)total phenolic acid content than the other extracts(Table 2).The range for the total flavonoid contents of the plant extracts was 3.05-9.65 mg QE/g.The total flavonoid contents of the different extracts were significantly different(P<0.05),except for Tulbaghia simmleri and Tulbaghia natalensis.Tulbaghia violacea had the highest total flavonoid content at 9.65 mg QE/g.

Antioxidant activity

TLC of phytochemicals:for qualitative analysis of the antioxidant capacities of the plant extracts,two TLC plates spotted with the plant extracts were placed in a mixture of benzene,ethanol,and ammonium hydroxide for separation.One TLC plate was sprayed with vanillin(Figure 1A)while other plate was sprayed with a solution of DPPH in methanol(Figure 1B)to visualize spots with antioxidant activities.24

DPPH is a stable free radical at room temperature,and it produces a violet solution in methanol.When the free radical reacts with an antioxidant,it loses its free radical property because of the termination of the reaction as it receives an electron or hydrogen from the antioxidant to become a stable molecule and it changes color to pale yellow.In the present study,extracts that produced yellow spots were considered to have antioxidant properties.All the samples showed numerous spots with different intensities(Figure 1B),which could be attributed to the different radical scavenging capacities of the extracts.

DPPH assay and ABTS assay:thein vitroantioxidant activities of the crude extracts were examined using DPPH and ABTS assays.The antioxidant activities of extracts from the eight Tulbaghia species were evaluated using the percentage scavenging activities(Figures 2,3)and IC50values(μg/mL)(Table 3).

Among the extracts,Tulbaghia violacea had the highest scavenging activities for both DPPH[0.01(43%)to 0.5 mg/mL(57%)]and ABTS[0.01(46%)to 0.5 mg/mL(70%)].DPPH:1,1-diphenyl-2-picrylhydrazyl;ABTS:2,2′-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid

The EC50values for the Tulbaghia extracts were determined(Table 3).A low EC50indicates that an extract is a strong DPPH radical scavenger.Among the extracts,Tulbaghia alliacea and Tulbaghia violacea had the lowest EC50values at 0.06 and 0.08 mg/mL,respectively,for the DPPH assay.For the ABTS assay,Tulbaghia leucantha and Tulbaghia violacea had the lowest EC50values,with both at 0.03 mg/mL(Table 3).Ascorbic acid was the strongest DPPH radical scavenger with an EC50of 0.0009 mg/mL.These results show that Tulbaghia alliacea and Tulbaghia violacea have the best antioxidant activities among the tested extracts as illustrated by both DPPH and ABTS assay.

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Table 1 Preliminary phytochemical analysis

Notes:++:present;--:absent.

Plant species Item Tulbaghia leucantha--++++--++++++++Alkaloids Flavonoids Glycosides Phlobatanins Tannins Terpenoids Saponins Steroids Tulbaghia acutiloba--++++--++++++++Tulbaghia alliacea--++++--++++++++Tulbaghia cernua--++++--++++++++Tulbaghia natalensis--++++--++++++++Tulbaghia Ludwigiana--++++--++++++++Tulbaghia simmleri--++++--++++++++Tulbaghia violacea--++++--++++++++

Table 2 Total phenolic acid and flavonoid contents of theTulbaghia species

Notes:the results presented are per gram of fresh material(mean±standard deviation,n=3).GAE:gallic acid equivalent;QE:quercetin equivalent.Within a column,identical superscript letters(a-i)show that the results between samples are not significantly different(P≥0.05),whereas different superscript letters show that the results are significantly different(P<0.05).

Total flavonoid content(mg QE/g fresh weight of sample)4.56±0.79c7.99±0.41d3.04±0.15e6.56±0.34f7.14±0.23g6.22±0.43h6.06±0.58h9.65±1.32iSample Tulbaghia acutiloba Tulbaghia alliacea Tulbaghia cernua Tulbaghia leucantha Tulbaghia ludwigiana Tulbaghia natalensis Tulbaghia simmleri Tulbaghia violacea Total phenolic content(mg GAE/g fresh weight of sample)5.12±1.96a9.21±2.88a4.50±1.44a6.70±1.63a7.64±0.94a7.01±1.44a6.70±0.94a11.10±1.44b

Figure 1 Thin layer chromatography plates for crude extracts sprayed with vanillin/sulfuric acid and 0.2%DPPH

A:vanillin/sulfuric acid;B:0.2%DPPH.Lanes contain the following samples:1:Trolox and acetone crude extracts;2:Tulbaghia acutiloba;3:Tulbaghia alliacea;4:Tulbaghia cernua;5:Tulbaghia leucantha;6:Tulbaghia ludwigiana;7:Tulbaghia natalensis;8:Tulbaghia simmleri;9:Tulbaghia violacea.DPPH:1,1-diphenyl-2-picrylhydrazyl.

Figure 2 Percentage scavenging activities of acetone crude extracts of the eightTulbaghia(T.)species Values are expressed as mean±standard deviation(n=3).Ascorbic acid was used as a standard.

Figure 3 ABTS scavenging activities of acetone extracts of the eightTulbaghia(T.)species Values are expressed as mean±standard deviation(n=3).Ascorbic acid was used as a standard.

Table 3 IC50values of the crude extracts ofTulbaghia species in acetone

Notes:DPPH:1,1-diphenyl-2-picrylhydrazyl;ABTS:2,2′-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid.

Sample DPPH(mg/mL)ABTS(mg/mL)Tulbaghia acutiloba Tulbaghia alliacea Tulbaghia cernua Tulbaghia leucantha Tulbaghia ludwigiana Tulbaghia natalensis Tulbaghia simmleri Tulbaghia violacea Ascorbic acid(μg/mL)IC50 0.16 0.06 0.21 0.39 0.26 2.70 0.39 0.08 0.0029 1/EC50 6.25 16.67 4.76 2.56 3.85 0.37 2.56 12.5 344 IC50 0.07 0.06 2.34 0.03 0.09 0.04 4.06 0.03 0.0009 1/EC50 14.29 16.67 0.43 33.33 11.11 25.00 0.25 33.33 1111

DISCUSSION

This study investigated the phytochemical contents and antioxidant activities of crude extracts from selected Tulbaghia species.Phytochemical analysis revealed the presence of flavonoids,glycosides,tannins,terpenoids,saponins,and steroids.The presence of these phytochemicals supports the utilization of some of the Tulbaghia species in various parts of South Africa,such as Eastern Cape,KwaZulu Natal,and Limpopo,where they are used to prepare traditional medications for treatment of various ailments.25-31,13These compounds are biologically active and may contribute to the antioxidant activities of the Tulbaghia species.The presence of flavonoids and terpenoids indicates these plant extracts potentially have antioxidant activities.Flavonoids are known to exert antioxidant activity through a scavenging or chelating process.32,33Scavenging of reactive oxygen species can counteract lipid oxidation in vitro and improve the body's antioxidant enzyme activity and decrease peroxide formationin vivo.34Terpenoids act as primary antioxidants by donating hydrogen to radicals,thereby slowing down lipid oxidation.35The presence of phytochemicals of interest(flavonoid and terpenoid antioxidants)suggests that further isolation,purification,and characterization should be carried out in future,and any isolated compounds could be used to design new pharmaceuticals.

Among the Tulbaghia species investigated in the present study,Tulbaghia violacea had the highest total phenolic acid and flavonoid contents(Table 2).Phenolic acids are a major group of primary antioxidants.36They are composed of one or more aromatic rings bearing one or more hydroxyl groups and can quench free radicals by forming stabilized phenoxyl radicals.37Flavonoids are important antioxidants with high redox potentials that allow them to act as reducing agents,hydrogen donors,and singlet oxygen quenchers.They can also chelate metals.Typically,flavonoids protect plants against ultraviolet light,fungal parasites,herbivores,pathogens,and oxidative cell injury.When consumed regularly by humans,flavonoids have been associated with a reduction in the incidence of diseases such as cancer and heart disease.38

Polyphenols have strong antioxidant activities associated with their abilities to scavenge free radicals,donate hydrogen,chelate metals,stop radical chain reactions,and quench singlet oxygenin vitroandin vivo.39Because the free radical scavenging abilities of these compounds are facilitated by their hydroxyl groups,the total phenolic acid and flavonoid contents could be used for rapid screening of antioxidant activity.Many studies have reported that phenolic acids possess other biological activities,such as anti-inflammatory,antiulcer,antispasmodic,antiviral,antidiarrheal,and antitumor properties.40,41Scavenging of reactive oxygen species by plant phenolic acids may be the basis of the purported human health benefits of plants.42Thus,quantification and subsequent identification of phenolic acids can provide vital information related to the antioxidant functions and potential health benefits of Tulbaghia species.

11 Ranglová K,Krejčová P,Kubec R.The effect of storage and processing on antimicrobial activity of Tulbaghia violacea.S Afric J Bot 2015;(97):159-164.

Although our results(Figures 2,3)showed dose-depen-dent antioxidant activity,it is clear that the plant extracts exhibited low radical scavenging abilities compared with the control(ascorbic acid).These findings correlate with results obtained by Soyngibeet al45for Tulbaghia violacea essential oil.Soyingbeet al44concluded that Tulbaghia violacea essential oil may not scavenge pre-existing free radicals,but it did show potential to prevent free radical generation through Fe2+chelation.

确定设防标准,收集小流域水文资料和实测资料,计算出行洪断面,预留沟道行洪宽度,确定沟道防洪治导线和生物砂堤具体位置。

Given the many known medicinal properties of Tulbaghia plants,the relatively low antioxidant activities observed in the present work do not imply these plants have low medicinal value.Antioxidant research has highlighted that low levels of phenolic acids(and other phytochemicals)and low antioxidant activities of the extracts do not translate to poor medicinal properties of the plant.46This may be because some plant-derived compounds are most effective when pure46,44but crude extracts were used in this study.

In conclusion,the bioactivities of the Tulbaghia species may be attributed to the phytochemicals that they contain.The total phenolic acid and flavonoid contents in the extracts indicate that Tulbaghia species are a potential source of antioxidants.The extracts from the eight Tulbaghia species tested exhibit potential antioxidant activities and are capable of scavenging reactive oxygen species.Thein vitroantioxidant activities of the plant extracts indicate that they could be used to prevent oxidative stress and associated disorders.However,further investigations are required to isolate and identify the compounds responsible for their antioxidant activities.The antioxidant activities of pure compounds could then be validatedin vivobefore clinical use.

REFERENCES

All experiments were performed in triplicate.The data were analyzed using Microsoft Excel and are expressed as mean±standard deviation(n=3).The IC50values were calculated using Graphpad Prism 7 for windows,Graphpad software,La jolla California,USA.Differences were considered to be significant whenP<0.05.

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传统的财务会计是在分权架构之上,以会计凭证为基础的工作,这样传统的工作方式,已经不能在当下大数据资料共享的前提下得到满足要求的工作效率,这不利于企业的进化和行业规范和标准的推广。计算机的发展,使得当下可以借助计算机的帮助实现大数据的集中管控,随后将数据交由管理会计进行数据的深度的分析,完成从海量信息中挖掘出对企业有价值的信息的工作,有着这些信息,可以更好的帮助企业进行以后的一系列决策。

9 Choi CW,Kim SC,Hwang SS,Choi BK,Ahn HJ,Lee MY,Park SH,Kim SK.Antioxidant activity and free radical scavenging capacity between Korean medicinal plants and flavonoids by assay-guided comparison.J Plant scie 2002;163(6):1161-1168.

10 Aremu AO,Van Staden J.The genus Tulbaghia(Alliaceae)--a review of its ethnobotany,pharmacology,phytochemistry and conservation needs.J Ethnopharmacol 2013;149(2):387-400.

Antioxidant activity denotes the ability of a bioactive compound to maintain cell structure and function by effectively clearing free radicals,inhibiting lipid peroxidation reactions,and preventing other oxidative damage.8It has been suggested that antioxidants could prevent many chronic diseases,such as cancer,diabetes,and cardiovascular disease.6Therefore,studies of natural antioxidants,such as those from medicinal plants,are important.34In the present study,qualitative screening revealed that all the extracts had antioxidant activity.Numerous spots with different intensities were observed on the TLC plates for all extracts after they were developed with DPPH(Figure 1).In the TLC results,the extracts that produced yellow spots were considered to have antioxidant properties.The appearance of a pale yellow color is based on inhibition of the accumulation of oxidized products because the generation of free radicals is inhibited by the presence of antioxidants.43,9In the present study,DPPH and ABTSin vitroassays were used to quantitatively evaluate the antioxidant activities of the eight Tulbaghia extracts.The degree of color change in these assays is proportional to the concentration and potency of the antioxidants.A large decrease in the absorbance of the reaction mixture indicates the tested compound has strong free radical scavenging activity.44Dose-dependent antioxidant activity was observed for all the extracts(Figures 2,3).The results obtained in this study suggest that the plant extracts contain phytochemicals that can scavenge free radicals by hydrogen donation and prevent potential damage.The antioxidant activities of plant extracts are often associated with the phenolic acids they contain.The high total phenolic acid and total flavonoid(Table 2)contents observed for Tulbaghia violacea correlate with its high antioxidant activity in the DPPH and ABTS assays(Figures 2,3).Plant phenolic acids are a major group of primary antioxidants.They can react with active oxygen radicals,such as hydroxyl radicals,superoxide anion radicals,and lipid peroxyl radicals,and inhibit lipid peroxidation at an early stage.The good scavenging ability of phenolic acids arises from their hydroxyl groups.

12 Zschocke S,van Staden J.Cryptocarya species-substitute plant for Ocotea bullata?A pharmacological investigation in terms of cyclooxygenase 1 and 2 inhibition.J Ethnopharmacol 2000;71(3):473-478.

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通过立法对人工智能的发展予以规范已成为共识,但立什么样的法和怎样立法却存在争议。从国家层面看,由于各国对待人工智能的态度不同,发展状况不一,在立法的目的上也存在不同,具体涉及立法的层次和监管的目的。

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在生命的遗言中,他写道:“只有在分享之时,幸福才是真实的…我的一生非常幸福,感谢上帝。再见,上帝保佑你们每一个人。”落款是“克里斯托弗·约翰逊·麦坎德斯”,就在几个月前,他还试图将这个名字从人间彻底抹去,而代之以“超级流浪者”,对名字的接纳宣告着他对自身“存在”的认同、对生命意义的全然接纳与领悟。

24 Bungu L,Frost CL,Brauns SC,Venter MVD.Tulbaghia violacea inhibits growth and induces apoptosis in cancer cellsin vitro.Afric J Biotechnol 2006;5(20):1936-1943.

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32 Zou Z,Xi W,Hu Y,Nie C,Zhou Z.Antioxidant activity of Citrus fruits.Food Chem 2016;196(1):885-896.

(4) 随着通入发动机气体质量流率的增大, 发动机内流场的压强不断升高, 气体总压增大, 因此注入单位质量流率所需要的能量也增大, 这是发动机效率降低的原因之一.

33 Grassmann J.Terpenoidss as plant antioxidants.15 Vitam.and Horm.2005;(72):505-535.

34 Fawole OA,Ndhlala AR,Amoo SO,Finnie JF,Van Staden J.Anti-inflammatory and phytochemical properties of twelve medicinal plants used for treating gastro-intestinal ailments in South Africa.J Ethnopharmacol 2009;123(2):237-243.

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Samkeliso Takaidza,Fanyana Mtunzi,Michael Pillay
《Journal of Traditional Chinese Medicine》2018年第2期文献

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