Study On The Hypoglycemic Activity Of Sweet Potato Leaf Polyphenols From Cultivar Simon No.1 And Its Mechanism

Sweet potato from cultivar Simon No.1 has extremely high pharmacological value.Its root yield is very low in the Central Plains area.On the contrary,its leaf growth is very vigorous and the yield is very high.The hypoglycemic activity of sweet potato leaves from cultivar Simon No.1 has been confirmed,and many studies have shown that the main hypoglycemic component is polyphenols.However,the specific individual phenolic compound which possesses high hypoglycemic activity is not clear,and the mechanism of hypoglycemic effect has not yet been clarified.In the present study,sweet potato leaves from cultivar Simon No.1 were used as raw materials.Firstly,polyphenols were extracted by ultrasonic-microwave assisted ethanol solvent method,and the sweet potato leaf phenolic acids?SPLPA?and sweet potato leaf flavonoids?SPLF?were separated and purified by AB-8 resins and liquid-liquid extraction,respectively.Then the individual phenolic composition of SPLPA and SPLF was identified by UPLC–Orbitrap–MS/MS and UPLC-DAD.Furthermore,the antioxidant and hypoglycemic activities in vitro of SPLPA and SPLF were elevated.The hypoglycemic activities and mechanism in vivo of SPLP were clarified by T2DM animal model.Finally,based on optimizing the blanching method and formula,Simon 1 sweet potato leaf powder product with hypoglycemic activity was developed.The main results are as follows:?1?Thirteen phenolic acids were identified in SPLPA,including 1-CQA,5-CQA,esculin,protocatechualdehyde,3-CQA,4-CQA,CA,7-hydroxycoumarin,3,4-CQA,3,5-CQA,4,5-CQA,3,4,5-CQA,ethyl caffeate,and the prominent component was 3,5-CQA?45.34±0.6%DW?.Ten flavonoids were identified in SPLF,including rutin,hyperoside,isoquercitrin,astragalin,quercetin,kaempferol,diosmetin,jaceosidin,chrysin,pectolinarigenin,and the major component was astragalin?28.07±0.73%DW??2?Protocatechualdehyde,ethyl caffeate and quercetin were also identified,exhibiting both excellent antioxidant capacities and strong inhibition of?-glucosidase and?-amylase.DPPH radical scavenging activity and FRAP antioxidant activity displayed a positive correlation with hypoglycemic activity in vitro.Kinetic analysis demonstrated that SPLPA and SPLF both reversibly inhibited?-glucosidase,in a mixed-type manner,with IC₅₀ values of 329.55±1.22 and 250.00±0.79?g/mL,respectively.?3?Oral administration of SPLP could significantly reduce weight loss and fasting blood glucose level?decreased 64.78%?compared with those of untreated group.Furthermore,improved glucose tolerance ability,increased hepatic glycogen?increased 126.78%?and muscle glycogen?increased135.85%?level,increased insulin level?increased 100.11%?,ameliorated insulin resistance and improve insulin sensitive index were observed in SPLP treatment group.SPLP also significantly reversed the dyslipidemia caused by diabetes.Histopathological observation confirmed that SPLP could relieve liver inflammation and maintain the integrity of islet structure by inhibiting?-cell apoptosis.qRT-PCR showed that SPLP could up-regulate the mRNA expression of PI3K/AKT/GSK-3?signaling pathway in liver and PI3K/AKT/GLUT-4 signaling pathway in muscle to enhance the activity of enzymes related to glycogen synthesis and glucose metabolism.?4?The total polyphenol and antioxidant activity of sweet potato leaf powder of uncut group were1.69 and 1.91 times those of cut group,respectively,and the index of nutritional quality of copper,manganese and vitamin E of uncut group were significantly greater than cut group.The ultrafine sweet potato leaf powder produced lowest gravitational sedimentation ratio?49%?,indicating it had greatest suspension stability.The optimized formula of sweet potato leaf powder-based beverage was as follows:ultrafine sweet potato leaf powder of uncut group was mixed with 2.5%?w/w,powder basis?xanthan gum,1%calcium lactate,2%ascorbic acid,12%maltodextrin,20%xylitol and 0.9%apple essence.In conclusion,the sweet potato leaf polyphenols from Cultivar Simon No.1 exhibited great hypoglycemic activity both in vitro and in vivo.Furthermore,the sweet potato leaf powder-based beverage has great potential for development in the natural hypoglycemic drug market.