Separation, Identification And Antioxidant Activities Of Polyphenol From Longan Peel And Seed

Research interest in polyphenolic antioxidants has increased remarkably in the last decade.In this study polyphenols were extracted and then purified from longan peel and seed.Their antioxidant activity by was determined by FRAP assay and scavenging DPPH free radical ability,and the phenolic structures were identified by HPLC-ESI-MS and MALDI TOF MS.The compositions of longan peel and seeds were analyzed.Results showed that longan peel contains abundant crude fibre(approximately 11%) and longan seeds contain 35%starch.Both longan peel and seed contain more than 4%polyphenols.A large variation of various phenolic contents and FRAP values in different parts(peel, pulp and seed) among 12 cultivars of longan in Fujian Province were observed.A positive linear correlation between antioxidant activity and contents of total polyphenols was established,which confirmed that polyphenol was a main contributor to its antioxidant activity of longan.Based on the FRAP values,the cultivars Wulongling,Youtanben,Dongbi,Bayizao and Shuizhang can be regarded as potential sources of antioxidants.Conditions for polyphenols extraction from longan peel and seed were optimized by orthogonal experiment:50%acetone aqueous(v/v),ratio of solid to liquid 1:100(g·mL^-1)(or 1:140 for seed),extracting for 2h under 70℃(or 50℃for seed) along with ultrasonic pretreatment for 20 min.The optimal yields of polyphenol with three repeated extraction from longan peel and seed were 52.9 and 62.1 mg·g^-1 of dry weight,respectively.Purification of crude extract by Sephadex LH-20 column chromatography yielded a total of seven and six fractions(LPCE-1～7 and LSCE-1～6),respectively. GA mainly existed in LPCE-2(7.49 mg·g^-1) and LSCE-3(36.75 mg·g^-1),and EA mainly existed in LPCE-4～5 and LSCE-2～4,whose maximal content was 81.22 mg·g^-1.27 phenolic compounds were identified by HPLC-ESI-MS including 10 unknown structures.MALDI TOF MS reconfirmed that the condensed tannins existed in longan peel,and their drgree of polymerization was from 2 to 10.The antioxidant activities of LPCE-2～7,LSCE-1～6,LPCE-Ⅱ～Ⅳand LSCE-Ⅱ～Ⅳ(obtained by extracting with different organic solvents) were evaluated by FRAP assay and scavenging DPPH free radical ability.As the results showed, LPCE-6,LSCE-2,LPCE-Ⅱand LSCE-Ⅱhad the highest antioxidant activity, respectively.It was inferred that the potent antioxidant activities of longan peel and seed were mainly attributed to hydrolyzed tannins.