Characterization And Antidiabetic Property Of Proanthocyanidins From Acacia Mearnsii Bark

A.mearnsii bark extract contains abundant proanthocyanidins,which is an important renewable natural polymer.Black wattle proanthocyanidins used to be used in industrial tanning and adhesive production.In folk people also use it as a hemostatic agent.A.mearnsii bark PAs is an important renewable polymer,which was used in industrial leather and adhesive production.In this paper,we combined the liquid phase electrospray mass spectrometry with the matrix-assisted laser desorption/ionization time of flight mass spectrometry to study the structure,composition,the type of flavonoid bond and degree of polymerization of A.mearnsii bark PAs.Results showed that the monomeric flavan-3-ol in A.mearnsii bark are the common catechin and not very common gallocatechin,polymeric PAs were consists of catechin,gallocatechin,robinetinidol and fisetinidol connected by C4-C8 or C4-C6 flavonoids bond,all the PAs detected in A.mearnsii bark were B types with degree polymerization ranging from 1 to 11 or molecular weight ranging from 290 Da to 3300Da,and none of them was galloylated.The result of ¹³C NMR further proved that the abundance of prorobinetinidol and profisetinidol,the existence of chemical bonds does not contain C-O-C and double carbon connection.Through further analysis,it was found that the diversity of its stereoscopic structure were tentatively revealed,among which the presence ratio of trans at C-2 predominated cis with the rating was about 2.7:1,Cis-trans at C-3 extension units and cis-trans at C-3 termination units were detected.The relative content of oligomeric PAs in A.mearnsii bark were up to 77%,and only 23%were polymeric PAs.In this paper,we also compare its property of PAs in A.mearnsii bark with some common and usual PAs.Their properties were characterized for contents,mass spectrometry and normal-phase HPLC.The results showed that the content of PAs and the total polyphenols content in A.mearnsii bark was the highest and the content of oligomers was the highest,PAs in pine bark are almost all the polymeric PAs,A Type PAs was only found in peanut skin,PAs and polyphenols in grape seed have the lowest contents but the presence of monomer catechin,epicatechin and gallic acid were exhibited.The inhibition of these four kinds of PAs against?-amylase and?-glucosidase were studied by using chemical method.It was found that the degree of polymerization was the main factor for inhibited the activity of?-amylase because the degree of polymerization of PAs in A.mearnsii bark was the lowest and the content of oligomers was highest,which but showed the highest percentage inhibition.A type PAs were only detected in peanut skin and its inhibition against?-glucosidase was the strongest,followed by PAs in A.mearnsii bark.Consequently,we can at least conclude that inhibition on?-glucosidase is related to the structure of PAs,and it may be also related to the unmber of–OH groups.In the experiments,the antioxidant properties of four kinds of PAs were determined by chemical-based method and cellular-based method.The results showed that the highest total polyphenol content of PAs in A.mearnsii bark showed the strongest antioxidant activity,and the results further indicated that the polyphenol was the major contribution for antioxidant activity.However,the EC₅₀ value obtained by chemical-based method was more than 10 times of the EC₅₀ value obtained by using the cellular-based method,we could think that it might due to molecular size of PAs that could not reach the cell to participate in the scavenging of reactive oxygen radicals.Based on the significant bioactivity of PAs from A.mearnsii bark,and gastrointestinal stability greatly influence the bioactivity of inhibition of?-glucosidase,herein we used the method of in vitro digestion to study the polyphenol content in A.mearnsii bark,bioavailability,antioxidant and inhibition of enzyme activity.These results showed that PAs from A.mearnsii bark was stable in the gastric environment and decomposed in the intestinal environment.The decomposition was confirmed by the normal-phase HPLC and gel chromatography,and about 53%of the inhibitory enzyme activity was reserved.A in vitro digestion study on bioavailability found that only the dimer,trimer of flavan-3-ol monomers could be absorbed into the dialysis bag,and the low bioavailability was related to its large molecular dimension and water solubility.It was found that antioxidant activity and?-glucosidase activity were related to the total polyphenols content,therefore,we further believe that there is a correlation between antioxidant and anti-diabetes properties.The PAs fractions with different mean degrees of polymerization were obtained by column chromatography and solvent extraction.Prorobinetinidol and profisetinidol predominated procyanidins and prodelphinidins was evaluated by using FT-IR.The fraction with lowest mean degree of polymerization was detected using LC/MS showed that the only presence of dimers and trimers.The bioctivity analysis of four PAs fractions showed that the oligomeric fraction showed the strongest antiproliferation effect,larger PAs showed the strongest enhancement of glucose consumption in HepG2 cells.However,the inhibitory effect of PAs fractions on?-glucosidase was not dominantly contribute by degree of polymerization,but related to the number of–OH groups.The above study demonstrated the potential of PAs from A.mearnsii for using as antiproliferation and regulating blood glucose balance.