Evaluation Of Extraction, Isolation And Antioxidant Activity Of Polyphenolic Of Sweet Potato Leaf (Ipomoea Batatas L.)

Many researches have been reported about sweet potato (Ipomoea batatas L.). However, little information about sweet potato leaves is available. Sweet potato leaves can be used as a source of tradional Chinese medicine indicating that the plants are rich of active ingredients. The source of sweet potato leaves is considerable in China. If we can change waste into valuables and make further processing of the plants, there will be important economic value and practical significance.The extraction optimization technics parameters of polyphenol of sweet potato leaf were studied. The total polyphenol content and the antioxidant activities of different varieties of sweet potato leaf were determined. Pushu 53 was found to be the preeminent candidates with relatively higher TPC as well as stronger antioxidant activities. The ethanol extract of Pushu 53 leaves was extracted with different organic solvents to obtain four fractions. TPC and the antioxidant activities of Pushu 53 extract and the four fractions were evaluated. The separation optimization technics parameters of polyphenol of sweet potato leaf with macro-porous resins were studied. High performance lipid chromatography and mass (LC-MS) were used for purification and identification of polyphenol of sweet potato leaf. The results were as follows:The effects on yield of extraction temperature, ethanol concentration, ratio of solid/liquid, extraction time, and extraction times were researched. TPC of different treatments were determined. The optimization technics parameters of TPC by orthogonal design of L₉(3⁴) were as follows: sweet potato leaf was extracted at 80℃in 70% ethanol for 40 min two times, with 1:25 as ratio of solid/liquid.TPC of 116 varieties of sweet potato leaf was determined by Folin-ciocalteu method. We found that TPC in leaves of different varieties of sweet potato were quite different, ranging from 1.22～3.02 times between different varieties. Also, the antioxidant activities of 8 varieties were determined by the DPPH (1, 1-diphenyl-2-picrylhydrazyl free radical), TEAC (Trolox equivalent antioxidant capacity), FRAP (ferric ion reducing antioxidant power) methods, chelating rate of Fe²⁺, reducing activity, and scavenging rate of·OH. Correlations between antioxidant activity and TPC were analyzed, respectively. The antioxidant activity determined by 5 methods all significantly correlated with TPC (R²>0.7728). The results show that TPC is the most active ingredient which shows excellent antioxidant activity. Among the 8 varieties, Pushu 53 leaves are the preeminent candidates with relatively higher TPC as well as stronger antioxidant activities. The ethanol extract of Pushu 53 leaves was extracted with different organic solvents to obtain chloroform fraction, ethyl acetate fraction, n-butanol fraction, and water fraction, respectively. TPC of ethanol extract and the four fractions was determined by Folin-ciocalteu method and the antioxidant activities were determined by the DPPH, TEAC, and FRAP methods. The result shows that ethanol extract and the four fractions of sweet potato leaf have excellent TPC and certain abilities of scavenging effects on free radicals and reducing Fe³⁺. Among ethanol extract and the four fractions, ethyl acetate fraction had the highest TPC and the strongest antioxidant activity.8 kinds of macro-porous resins were compared for the separation of polyphenol of sweet potato leaf. HP20 resin exhibited superior adsorption and regeneration properties. The optimum conditions for separating and purifying sweet potato polyphenol were obtained. Then, LC-MS were used for purification and identification of polyphenol of sweet potato leaf. The results showed that the separation optimization technics parameters with HP20 resin were as follows: the sample concentration is 1.2 mg/ml, pH value is 4, the moving speed is 2 ml/min, adsorbing twice, and eluting volume is 4 BV with 70% ethanol as eluting solvent. The purity of polyphenol of sweet potato leaf can be improved from 11.46% up to 42.29% and the recovery rate is 79.27%.The polyphenol of sweet potato leaf was analyzed by HPLC and LC-MS. The results indicate that the main phenolic substances in sweet potato leaf are caffeyol qunic acid (CQA) derivatives, including chlorogenic acid (CHA), 3,4-diCQA, 3,5-diCQA and 4,5-diCQA. Great difference had been found between total polyphenol content of different varieties of sweet potato leaves but little difference were found between the composition of polyphenol. The purity of the ethanol extract of Pushu 53 leaves were significantly improved after purified by HP20 macro-porous resin and the polyphenol content is 32.92%.