Extraction,Purification,Compositional Analysis And In Vitro Digestion Of Purple Sweet Potato Polyphenols

Purple sweet potato belongs to Convolvulaceae,which generally distributed in most areas of southern China.It is rich in nutrients,except the tubers contain polysaccharide,protein,vitamins,but also an excellent source of anthocyanins,chlorogenic acid,flavonoids and other polyphenols.Polyphenol is a natural antioxidant with a series of functions such as blood lipids,anti tumour,remove free radicals and anti-aging.The current research on polyphenols is mainly on extraction and determination of the free phenol.There is another form of phenol,which exists in combination state known as bound phenol.The study about extraction and bioactivity of bound phenol from the plant system is rarely reported,so "Liaoshu 20" was chosen as a raw material to optimize the process of the free phenol and bound phenol extraction and purification method.High performance liquid chromatography and LC-MS been used to isolated and identified polyphenol monomer.In vitro digestion test and antioxidant activity test are also in progress.Here are the results:1.Using 60%ethanol as organic solvent to extract free phenol from purple sweet potato.The optimal extraction conditions are the theoretical value act as temperature is 50.12?,the ratio of liquid to solid is 55.43:1(mL/g),the extraction time is 2.12h.From the view of practical application,the extraction conditions were modified to 50?,55:1(mL/g)and 2h.With the optimized parameters,free phenol extraction is(1.06±10.001)g/100g,about 98.88%of theoretical value.Free phenol was completely abstracted before bound phenol extraction from the Purple sweet potato residue by alkali.The optimal predictive value of bound phenol extraction is:the ratio of liquid to material is 32.2:1(mL/g),concentration of NaOH is 1.87mol/L,hydrolysis time is 5.22h,rate of extraction reached 0.58g/100g.After optimizing the process parameters,when the ratio of liquid to material is 30:1(mL/g),NaOH concentration is 2mol/L,hydrolysis time is 5h,the extraction rate of polyphenols could be reaching(0.57±0.008)g/100g,which about 97.34%of the predicted value.2.The research showed that AB-8 macroporous resins exhibited the excellent characteristics for free phenol.Here are the optimum conditions of adsorption:the concentration phenols is 1.0 mg/mL,the pH of sample is 3.0,loading volume is 5.4BV.The optimum conditions of desorption are using 50%ethanol as eluent,volume is 6.8BV,pH is 7.0.HPD-100 was selected as the best macroporous resin for bound phenol.The optimal extract sample concentration is 0.2mg/mL,the pH of sample is 3.0,the maximum sample volume is 3.6BV,desorption of the optimal eluent is 50%ethanol solution,pH is 3.0,elution volume is 6.8BV.The content of phenolic compounds was significantly higher after purification,indicating that the macroporous resin has good purification effect on purple potato polyphenol.3.Using HPLC-MS to identify free and bound phenol extracts from purple sweet potato,which including Chlorogenic acid,Caffeoyl-methylquinic acid,Dicaffeoylquinic acid,Methylated diacaffeoylquinic acid and Hydroxybenzoic acid,Caffeic acid.Then the Isochlorogenic acid,Isochlorogenic acid A,Isochlorogenic acid B,Isochlorogenic acid C and P-hydroxybenzoic acid were identified in free and bound phenol respectively by HPLC.The purified samples were detected their activities of scavenging DPPH free radical and inhibiting alpha glucosidase.The result showed that the median inhibitory concentration(IC50)of scavenging DPPH free radical is 0.014mg/mL for free phenol and 2.02mg/mL for bound phenol.The IC50 of inhibitory effect on a-glucosidase is 0.16mg/mL for free phenol and 0.98mg/mL for bound phenol.4.By simulating organism gastrointestinal digestion to discuss the release,absorption and stability of polyphenol in purple sweet potato.Results showed that:the optimal time of in vitro gastric and intestinal digestion is 1h and 2h respectively.Bioavailability of polyphenols,flavonoids,anthocyanin and phenolic acids are(18.42±0.33)%?(15.00±0.21)%?(0.46±0.006)%and(12.87±0.12)%.Except phenolic acids,the content of polyphenols,flavonoids and anthocyanins were decreased during free phenol digestion,while the content of flavonoids,anthocyanins and phenolic acids were increasing during bound phenol digestion,which showed that the stability of bound phenol is better than free phenol.Purple sweet potato after digestion,the content of polyphenols,flavonoids and phenolic acids were increasing,which probably because a part of free phenol was converted to bound phenol.