Research On Phenolic Compounds And The Antioxidant Activity Of Lotus Seed Epicarp Residue

In this study,lotus seed epicarp residue(the processing byproduct of lotus seed)were taken as experimental materials.The extraction conditions of phenolic compounds from lotus seed epicarp residue were optimized.The total phenolic content,total flavonoid content and total proanthocyanidin content of lotus seed epicarp were determined.The antioxidant activity and a-glucosidase inhibitory activity of lotus seed epicarp residue extract were also evaluated.Besides,UPLC-Triple-TOF/MS analysis was employed to identify and characterize the main bioactive compounds in lotus seed epicarp residue.This study is aiming at offering practical basic theory for valuable use of lotus seed epicarp residue.The results of this study were listed as follows:(1)The Box-Behnken design was used to optimize the ultrasonic-assisted extraction conditions of phenolic compounds from lotus seed epicarp residue.In the basis of single factor experiment,choosing 70%acetone as extraction solvent,the optimized extraction conditions were predicted by response surface methodology as follows:solid to liquid ratio at 1:25.49 g/mL,extraction time at 1.58 h,extraction temperature at 49.90?.Under the optimized extraction conditions,the predicted response values for total phenolic content,total proanthocyanidin content and DPPH+ scavenging capacity were 194.31 mg GAE/g DW,242.99 mg CE/g DW,238.60 mg AAE/g DW,respectively.Actual validation values were corresponding to predicted values and the model desirability was 98.3%.(2)In the basis of optimized extraction conditions,three different solvents(70%methanol,70%ethanol,70%acetone)were used as extraction solvents and their effects on main phenolic compounds content in lotus seed epicarp residue extract from three cultivars(Liyebailian,Shilihehua,Jianlian)were evaluated.The results showed that,for extracts with different extraction solvents of lotus seed epicarp residue from the same cultivar,their main phenolic compounds content order was:70%acetone>70%methanol>70%ethanol.The 70%acetone extract for three cultivars obtained total phenolic content in the range of 105.64~194.54 mg GAE/g DW,total flavonoid content in the range of 40.59~78.72 mg CE/g DW,total proanthocyanidin content in the range of 136.88~243.15 mg CE/g DW.For extracts extracted with same solvent,lotus seed epicarp residue from Liyebailian cultivar obtained highest total phenolic content,total flavonoid content and total proanthocyanidin content among three cultivars.(3)The antioxidant activity of extracts with different extraction solvent of lotus seed epicarp residue from Liyebailian,Shilihehua and Jianlian was measured.For extracts with different extraction solvents of lotus seed epicarp residue from the same cultivar,their antioxidant activity order was:70%acetone>70%methanol?70%ethanol.The 70%acetone extract for three cultivars obtained DPPH+ scavenging capacity in the range of 117.68~238.53 mg AAE/g DW,ABTS·+ scavenging capacity in the range of 2802.04~7973.18 mg AAE/g DW,ferric ion reducing antioxidant power in the range of 81.72~223.85 mg AAE/g DW.The antioxidant activity of lotus seed epicarp residue extract from Liyebailian cultivar was higher than that of lotus seed epicarp residue extract from Shilihehua and Jianlian cultivar.(4)The a-glucosidase inhibitory activity of extracts with different extraction solvent of lotus seed epicarp residue from Liyebailian,Shilihehua and Jianlian was evaluated.In the a-glucosidase inhibition assay,for lotus seed epicarp residue from three cultivars,IC50 of their 70%acetone extract was in the range of 5.73~6.69 ?g/mL,IC50 of their 70%methanol extract was in the range of 7.83~13.38 ?g/mL,IC50 of their 70%ethanol extract was in the range of 9.29~17.30 ?g/mL.The a-glucosidase inhibitory activity of above all lotus seed epicarp residue extract was significantly higher than that of the positive standard acarbose with IC50 of 1293.31 ?g/mL.The results showed that 70%methanol,70%ethanol and 70%acetone extracts of lotus seed epicarp residue all obtained extremely high a-glucosidase inhibitory activity,among which 70%acetone extract had highest a-glucosidase inhibitory activity.(5)UPLC-Triple-TOF/MS was used to separate and identify main bioactive compounds in lotus seed epicarp residue.A total of thirty kinds of bioactive compounds were identified,including six phenolic acid(gallic acid,neochlorogenic acid,catechol,ellagic acid,caffeic acid and p-coumaric acid),nine flavonols(quercetin,isorhamnetin,kaempferol,rutin,hyperoside,isoquercetin,isoquercetin 7-O-glucuronide,kaempferol 3-O-glucoside,myricetin 3-O-glucuronide),three flavanols(catechin,epicatechin,(epi)gallocatechin),eight proanthocyanidins(four proanthocyanidin dimer,three proanthocyanidin trimer and one proanthocyanidin tetramer)and four unsaturated fatty acids.