Research On Antioxidant Activity And Material Basis Of Hibiscus Flowers

Hibiscus syriacus,Malvaceae hibiscus,is a common garden shrub species,which widely distributed in tropical and subtropical regions of China.Hibiscus syriacus flowers has long flowering period,which is colorful and showy with fleshy hypertrophy and high yield.It can be used as medicine and can be eaten.With the construction of the beautiful countryside,Planting areas of Hibiscus syriacus are expanding,flower yield also increases year by year.But most of them have not been utilized in scale and then wither down,which is a waste of valuable resources.Therefore,this paper makes a comparative study on the antioxidant activity and material basis of Hibiscus syriacus.(1)The comparison of the bioactive substances of five cultivars of Hibiscus syriacus flowers showed that the contents of polyphenols and total flavonoids from high to low in turn were Hibiscus syriacus L.,Hibiscus syriacus.f.paeoniflorus,Hibiscus syriacus.cv.’Lavandula Chiffon’,Hibiscus syriacus.cv.’shigyoku’ and Hibiscus syriacus.f.elegantissimus.The order of antioxidant activity of all cultivars was basically the same as their polyphenols and total flavonoids.The content of polyphenols and total flavonoids in the Hibiscus syriacus L.was the highest,which reached 17.33 mg GAE/g and 12.68 mg RE/g,respectively.And it’s antioxidant activity was the strongest,whose total reduction ability(FRAP),1,1-diphenyl-2-picrylhydrazyl(DPPH)radical scavenging ability and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)free radical scavenging ability were 1.58 mmolFeS04/g,6.82 mg TE/g and 17.96 mg TE/g,respectively.There was a significant correlation between the antioxidant activity and the content of polyphenols and total flavonoids(P<0.01),but the correlation with anthocyanin content was not significant(P>0.05).On the basis of single factor experiments,response surface method was used to optimize the extraction process of active substances from Hibiscus syriacus flowers.The optimal extraction parameters were:liquid-material ratio 37:1(mL/g),extraction time 47 min,ethanol concentration 73%,ultrasonic power 125 W.Under the optimized conditions,the total flavonoids yield was 16.27 mg/g,and the total phenol yield was 19.19 mg/g.Different polar solvent extracts of Hibiscus syriacus L.had a certain antioxidant activity.The highest total reduction capability(6.16 mmol FeSO4/g)was observed in the n-butanol extract and it showed the best DPPH scavenging ability(15.50 mg TE/g)and ABTS scavenging ability(40.71 mg TE/g).The correlation between active substance content and antioxidant activity of different polar solvents extracts showed that antioxidant activity(FRAP method,DPPH method and ABTS method)and the total flavonoid content was significantly correlated(P<0.01 and the correlation coefficient R was 0.837,0.915 and 0.762(P<0.01).It indicated that the material basis of antioxidant activity of Hibiscus syriacus flower was mainly due to the flavonoids.(2)The results of using macroporous resin to separate and purify flavonoids from Hibiscus syriacus flower showed that X-5 resin was the most suitable for purification of flavonoids in Hibiscus syriacus flower.The purification process used flavonoids extract 0.5 mg/mL,flow rate 6 BV/h,water washing volume 4 BV,95%ethanol solution for dynamic elution and eluent flow rate 2.5 BV/h,and it can increase the content of flavonoids of Hibiscus syriacus flower to 61.32 mg/g.(3)Using HPLC and HPLC-QTOF to analyze the strongest antioxidant activity of n-butanol extract,combined with the comparison of the standard products,8 kinds of antioxidants were preliminarily identified:Kaempferol-O-hexose-C-hexose glycoside,apigenin,kaempferol-O-hexose-C-hexose glycoside isomers,apigenin-C-diglucoside,apigenin-Glucose glycoside,kaempferol-3-O-rutinoside,apigenin-7-O-rutinoside,cyanidin-3-malonyl glucoside.