Solvent Extraction Of Polyphenols From Sweet Potato Leaves And Study On Its In Vitro Digestibility,in Vivo Antihyperlipidemic Effects

Sweet potato leaves are the main byproduct of sweet potato production.In some regions of the world,they are generally eaten as green vegetables,for rich in polyphenols,proteins,vitamins,minerals and some functional microcomponents.Previous studies indicated sweet potato leaf extract exhibited various health-promoting biological activities,such as antioxidant activity,anti-mutagenicity,anti-cancer,anti-carcinogenesis,anti-microbial,anti-diabetes,anti-inflammation et al.Our group also studied the high utilization of SPL,and revealed that DHPM can accelerate the extraction of sweet potato leaf polyphenols and the antioxidant activities of extracts were also higher.However,some important function properties,for example,in vitro digestibility and antihyperlipidemic effects of the extracts obtained by DHPM assisted extraction still remained unknown.To solve these scientific problems,in this paper,we studied the high effective extraction of sweet potato leaf polyphenols in the basis of our preliminary studies,and the in vitro digestibility and antihyperlipidemic effects of DHPME were also investigated.At last,we established a HPLC method for simultaneous determination of five phenolics and one flavonoid in sweet potato leaves.This study was expected to provide useful information for the further research and utilization of sweet potato leaves in food industry and pharmacology.The main contents and conclusions are listed as follows:(1)Choosing ten different solvents,including water,aqueous methanol,aqueous ethanol and aqueous acetone to investigate the effects of solvents on the recovery and antioxidant activities of polyphenols from sweet potato leaves.Results indicated that the total phenolic content in extracts ranged from 23.28 to 43.82 mg CAE/g DM,and 70% ethanol extract had the highest total flavonoid(3.36 mg QE/g DM)and anthocyanin(36.49 mg c-3-gE/100 g DM)contents.While,50% acetone extract exhibited the highest crude extract yield(33.43% in dry materials),total phenolic content(43.82 mg CAE/g DM),as well as the strongest in vitro antioxidantactivities.A good correlation was observed between total phenolic content and antioxidant activities.Totally 14 phenolics were identified or tentatively identified in50% acetone extract,caffeoylquinic acid(CQA)and quercetin derivatives were indicated as the most abundant phenolics.The fact that different solvents exhibited different extraction efficiencies on 3-CQA,caffeic acid,3,4-,3,5-and 4,5-diCQA in sweet potato leaves,and 70% acetone showed the highest extraction capacity for 3,4-,3,5-and 4,5-diCQA also revealed by HPLC.(2)A simple and fast HPLC method for simultaneous determination 5 phenolic acid and 1 flavonoid in sweet potato leaves was developed.We also used this method to determine these phenolic compound in four areas in Jiangxi province.Sweet potato leaf polyphenols were separated within 20 min.Separation of these compounds was achieved on an Agilent ZORBAX SB-C18 column(4.6 mm × 250 mm,0.25 ?m).The mobile phase was consisted of water with 0.1% formic acid(phase A)and acetonitrile(phase B),and the seperation mode was gradient elution(0~12 min,10%?25%B;12~25 min,25% B;25~30 min,30%?40%B).The flow rate was 0.8 mL/min.The detection wavelengths were set at 326 for 5 phenolics and 355 nm for Quercetin-3-O-glucoside.The linear range of chlorogenic acid,caffeic acid,3,4-diCQA,3,5-diCQA,4,5-diCQA and Quercetin-3-O-glucoside were0.5~ 50.0 ?g/mL,0.5~ 25 ?g/mL,5.0~100 ?g/mL,10.0~200 ?g/mL,5.0~100 ?g/mL and 0.5~50 ?g/mL,respectively.And the average recovery was 99.34%,101.5%,102.68%,97.50%,96.90%,96.14%,respectively.This method is suitable to determine polyphenols in sweet potato leaves.We also found sweet potato leaves obtained in NanChang JiangXi province had the highest polyphenols,suggesting we had choosed a good material for our experiment.(3)The infuence of in vitro gastrointestinal digestion on the stability and bioaccessibility,as well as the in vitro antioxidant activities of polyphenols from sweet potato leaves were investigated.Two extracts,namely CSE(the conventional solvent extraction)and DHPMAE(dynamic high pressure microfluidization-assisted extraction)were taken as samples.Total phenolic content,antioxidant activities were evaluated among the digested and undigested samples.In addition,the phenolic profile of digestion juice were tested.The results indicated sweet potato leafpolyphenols were quite stable under gastic conditions.However,a significant decline was observed after the intestinal digestion,the bioaccessibility of CE and DHPME were 16.24% and 13.36%,respectively,indicating only a small portion of sweet potato leaf polyphenols can be absorbed by human body.The antioxidant activities of the extract(TEAC,RP)in the gastic digestion stage didn't change,however enhanced in the intestinal digestion stage.DHPM can enhanced the yield of polyphenols of sweet potato leaves,however,DHPM didn't increase the bioaccessibility of polyphenols.Despite the decrease of TPC of sweet potato leaf extracts in digestion,the results suggest that sweet potato leaves are still an important source of bioaccessible constituents after digestion,they are still potent as antioxidant.(4)The in vivo antihyperlipidemic effects of DHPME were investigated by creating a hyperlipidemic rat model.Results indicated that,after a high fat diet for50 days,the serum TC and LDL-C level of ICR rats were significantly increased,and much higher than the normal group.The liver index was also increased,and the colour of the liver surface were turned from scarlet to yellow.However,the body weight didn't show any difference than the normal group.By giving sweet potato leaf extract through stomach feeding,the serum TC and LDL-C decreased,but didn't show any difference.The liver appearance and liver biopsy both revealed that sweet potato leaf extract of medium dose and low dose can not improving the liver function,however,a high dose can.