Study On Antioxidant Activities And Antioxidative Substance Basis Of Maca (Lepidium Meyenii Walp.)

Maca （Lepidium meyeni） is a plant of the Brassicaceae family growing originally at4000～4500meters altitude in the Andean region of Peru．Maca has attracted attention frommany countries around the world, as it has multiple biological functions such asfertility-enhancing, anti-fatigue, improving sexual function, antioxidant, inhibition prostatehyperplasia, reducing menopause syndrome and increasing immunity function. Researchersrecognized these functions were correlative with maca secondary metabolites includingalkaloids,polyphenol, glucosinolates and sterol, and several functions were also attributable toantioxidant. Therefore studies on antioxidant and active substance basis are important forrevealing reactive mechanism and development of functional products.In this study, HPLC, LC-ESI/MS and colorimetry have been applied to analyzecompositions and contents of alkaloids,polyphenol, glucosinolates and sterol in three colortypes of maca cultivated in Yunnan, meanwhile the methods analyzing secondary metaboliteshave been established. In addition, the crude extract solvent was confirmed by antioxidantactivity evaluation in vitro. Then the crude extracts of maca were separated into severalfractions of different polarities based on the bioassay guided method. The fractions whichshowed best antioxidative activity were selected to separate into six constituents by silica gelcolumn chromatography. The antioxidative substance basis was revealed by relativity analysisbetween antioxidative activity and the content of secondary metabolites of six constituents.Further, the antioxidative capacities of constituents were confirmed by resisting injury toH₂O₂-induced damage cells. The main results are as follow:1. Analysis of secondary metabolites compositions and contents in macaThe acidic dye colorimetry is more appropriate for the determination of total alkaloids inmaca cultivated in Yunnan, The conditions of method are: determination wave414nm,dibromothymol-sulfonphthalein dye pH7.0, dye volume5.0mL. The contents of total alkaloids in purple, yellow and white maca were4.4078,2.2241and2.9193mg/g, respectively, thedifference between3color types maca is significant （P＜0.01）. The content of total alkaloidsin purple maca is the highest. which is close to the content of total alkaloids in maca grown inPeru.HPLC and LC-ESI/MS were applied to analyze glucosinolate compositions and contentsof3color types maca cultivated in Yunnan. Three color types of maca contain the samecompositions of glucosinolate, which are benzyl glucosinolate and methoxybenzylglucosinolate.The content of benzyl glucosinolate is higher than that of methoxybenzylglucosinolate.The result was consistent with that of sample cultivated in Peru. The totalglucosinolate contents in purple, yellow and white fresh samples were50.14,46.35, and84.57μmol/g, respectively, with a significant difference （P＜0.01）. Among them, the content ofglucosinolate in white sample is highest. The contents of dried samples were much lower thanthat in fresh samples. The contents of glucosinolate in sample processed by two dry techniquewere different significantly（P＜0.01） too, which showed that effect on glucosinolatehydrolyzed of processing condition was obvious.The compositions and contents of sterols in three color types of maca cultivated in Yunnanwere analyzed by GC-MS．The result showed that all the three types of maca containedβ-sitosterol and campesterol． The content of β-sitosterol was higher than that ofcampesterol．The total sterol contents in white，purple and yellow samples were36.60，32.38，27.97mg/100g，respectively．Among them，the total sterol content in white sample was thehighest．The difference in contents was significant among the three types of sample（P＜0.01）．The composition was consistent with that of sample cultivated in Peru.The contents of total polyphenol in three color types of macacultivated in Yunnan wereanalyzed by Folin-Ciocalteus method. Result indicated that the total polyphenol contents inpurple, yellow and white were35.08,4.05,3.57mg/g，respectively, with a significantdifference （P＜0.01）, the content of polyphneol in purple maca is highest.2. Study on extraction of antioxidative components and the strongest antioxidativefraction The antioxidative activities of components extracted by methanol and ethanol withvarious concentration from maca were determined by evaluating ferric reducing antioxidantpower, scavenging capacity of superoxide anion and hydroxyl free radical, inhibition of lipidoxidation. Result showed70%ethanol was appropriate extract solvent for anitoxidativecomponents in maca, The results indicated that ethanol extracts of3color types of macacultivated in Yunnan all had antioxidative activities, among them, the activity of purple macawas highest,and the activity of yellow maca was higher than that of white maca. It was foundthat the chloroform fractions in purple and yellow maca had the strongest antioxidativecapacities by using the bioassay guided method. The antioxidative activities of chloroformfractions and activity constituents separated from chloroform fractions were also confirmed byresisting injury to H₂O₂-induced damage cells, the protective effects of constituents separatedfrom chloroform fractions by silica gel column chromatography were visible in this test.3. Study on antioxidant substance basis of macaThe relativities were studied between antioxidative activity and the content of secondarymetabolites of constituent separated from chloroform fractions by correlation and linearregression statistic analysis.Result indicated the contents of polyphenol and alkaloids hadsignificant linear correlation with reducing antioxidative capacity, scavenging capacity ofhydroxyl free radical and inhibition of lipid oxidation （P＜0.01） in yellow maca. The resultalso showed that antioxidant capacities resulted from synergic action of polyphenol andalkaloids. In purple maca the contents of polyphenol and alkaloids had significant linearcorrelation with reducingl antioxidative capacity （P＜0.01）. The research reveals thatpolyphenol and alkaloids are the most important substance basis for antioxidation. of maca.