Study On The Interaction Between The Structural Units Of Feruloylated Oligosaccharides And The Antioxidant Mechanism

Feruloylated oligosaccharides(FOs)as the main component of grain of phenol and attention.FOs is a bound ferulic acid,so it has good antioxidant activity.However,the interaction between structural units of FOs and the mechanism of its antioxidant activity have not been clarified.In this study,FOs components with high,medium and low degree of polymerization were prepared by enzymatic hydrolysis of wheat bran fiber.By theoretical analysis,chemical analysis and the quantitative evaluation of the antioxidant capacity of each composition,further analysis of the structure unit of oligosaccharides to ferulic effect on the activity of acyl of phenol.Finally,the geometrical model of FOs components was constructed and the antioxidant activity fraction and size of FOs components were predicted by density functional method,thus revealing the antioxidant activity mechanism of FOs components.The main conclusions are as follows:(1)Preparation of feruloylated oligosaccharides with different degrees of polymerization.After purified by Amberite XAD-2 macroporous resin column,the FOs components were separated by Sephadex LH-20 gel chromatography column.The results showed that all the separated components exhibited feruloylated oligosaccharide structure and were composed of ferulic acid and arabinoxylan glyosomes with different degree of polymerization by ester bond.With the extension of elution time,the degree of polymerization of each component decreased.The results showed that FOs components with different degree of polymerization(xylose number)could be prepared by enzymatic hydrolysis of wheat bran fiber.(2)Evaluation of antioxidant capacity of feruloylated oligosaccharides with different degrees of polymerization.The results of Cyclic Voltammetry showed that the oxidation potential of FOs components with different polymerization degrees was lower than that of ferulic acid,which indicated that FOs components had good antioxidant capacity.The results of Differential Pulse Voltammetry showed that there was a good linear relationship between the oxidation peak current and the concentration in the range of 2.5?8.0 mg/m L.The free radical scavenging results showed that when the concentration was 8.0 mg/m L,the free radical scavenging rates of FOs-low,FOs-medium and FOs-high fractions with different polymerization degrees reached 69.02%,64.85%and 53.34%,respectively.The results showed that the FOs component had antioxidant capacity in a concentration-dependent manner.The order of activity of FOs components with different polymerization degrees was:FOs-low?FOs-medium>FOs-high.(3)Study on the interaction between the structural units of feruloylated oligosaccharides.Different proportions of ferulic acid-xylo-oligosaccharides compound content of the radical scavenging activity test shows:with the increase of xylose ratio,the IC₅₀ values of·OH free radical and DPPH·free radical scavenging of the complex increased gradually,that is,the ability of the complex with high xylose ratio to scavenge free radicals decreased gradually.The results show that the antioxidant activity of ferulic acid as the FOs component main structure unit.The Isbolographic analysis showed that the effect points of the ferulic acid-xylo-oligosaccharides were all located in the left quadrant of the additive line and the 95%confidence limit.The experimental IC_50mix of the complex with different proportions were all lower than the theoretical IC_50add,and the interaction index?was<1.The results indicated that there was synergistic antioxidant effect between ferulic acid and xylo-oligosaccharide,and the introduction of oligosaccharide groups in the composition structure of FOs might contribute to its antioxidant activity.Further statistical analysis showed that the interaction index?value between ferulic acid and xylo-oligosaccharide gradually increased with the increase of the xylose ratio,that is,the synergistic effect between ferulic acid and xylo-oligosaccharide weakened.The results indicated that the introduction of groups with high degree of polymerization may be detrimental to the antioxidant activity of FOs components.(4)Antioxidant activity mechanism of feruloylated oligosaccharides.Density Functional Theory was used to construct FOs components with low,medium and high degree of polymerization.All molecular structures were optimized,and parameters such as frontier orbital energy levels,natural charge layout,spin density distribution,ionization potential and bond dissociation enthalpy were calculated.The phenolic hydroxyl O-H bond of FOs component is longer than that of FA,so the activity of the phenolic hydroxyl on the parent ferulic acid of FOs component is better than that of the free FA.In addition,the hydroxyl on the xylo-oligosaccharide unit may also provide H atom and have antioxidant activity.The natural orbital charge(e)on the phenolic hydroxyl group of FOs fractions with different degrees of polymerization was greater than that of the far-end glycogen hydroxyl group.It was concluded that the phenolic hydroxyl group(OH_A)on the parent ferulic acid was the main antioxidant activity of FOs fractions.The Highest Occupied Molecular Orbital(HOMO)electron cloud of FOs component is mainly distributed on feruyl group,which indicates that feruyl group is the main active unit of FOs comp onent.The theoretical order of antioxidant activity of ferulic acid and FOs components with different polymerization degrees was as follows:FOs-medium?FOs-low>FO-high>FA.