Extraction And Characterization Of Pectin And Phenolics From Mangosteen Rind

To investigate the extraction, characterization of pectin and phenolics(proanthocyanidins and phenolic acids) from mangosteen rind, mangosteen rind pectin was extracted by hot acid method, FTIR, titration, UV-Vis spectroscopy, HPLC and rotational rheometer were applied to analyze its chemical and rheological properties, such as functional groups, galacturonic acid(Gal A) content, degree of ester(DE), neutral sugar contents, molecular weight and viscoelasticity in both solution and gel states. For phenolics, solid-liquid extraction and column chromatography were used to isolate proanthocyanidins and phenolic acids. They were then identified by ESI-MS, and quantified by reverse-phase and normal-phase HPLC. Free radical scavenging capacity of phenolic compounds were also evaluated through DPPH and ABTS assays. Main results show as follows.1. Mangosteen rind pectin extracted by hot acid method yielded 4.48 % to 8.49 %. The extraction yields increased with decreasing p H before p H 3, then kept stable at p H 3~6. It also increased with the uprising temperature, and obtained most when extraction time were between 1.5 h and 2 h. So the recommending extraction condition was p H 2, 80 ℃, 1.5 h.2. Mangosteen rind pectin belonged to high methoxyl pectin, its DE value and Gal A content were 75.97±3.49 % and 626.52±24.15 mg/g, respectively. It consisted of several neutral sugars: arabinose(17.91±1.33 mg/g), mannose(13.08±2.94 mg/g), glucose(9.83±1.67 mg/g), xylose(8.50±1.08 mg/g), galactose(7.88±0.88 mg/g), and rhamnose(4.32±0.83 mg/g). And its weight-average molecular weight was(7.69±0.50) ×105.3. Mangosteen rind pectin solution was pseudoplastic fluid, as its viscosity decreased with increasing shear velocity. Its rheological property fitted Ostwald-de Wale model: y = 0.3349x0.6363(R2 = 0.9771). Comparaing with commercial apple pectin gel, mangosteen rind pectin gel had narrower elastic defoarmation range and lower intensity in its gel net strength.4. Mangosteen rind had higher content of proanthocyanidins than its calyx and pulp parts. The contents of mangosteen rind extractable proanthocyanidins(EP) were 113.71±4.43 mg GAE/g by Folin-phenol assay, 19.20±0.73 mg catechin/g by DMAC assay, and 131.69±11.24 mg procyanidin B2/g by HPLC. Its mean degree of polymerization(m DP) was 4.27±0.08. While the content of nonextractable proanthocyanidins(NEP) was 36.92±2.38 mg procyanidin B2/g by HPLC, and its m DP was 5.41±0.04. Three extractable proanthocyanidin polymers were identified, they were type B procyanidin dimer, trimer and tetramer.5. The contents of three non-Na HCO3 purified(PA-A) and Na HCO3 purified(PA-B) phenolic acid extracts were: protocatechuic acid(0.99±0.04, 1.35±0.08 mg/g), chlorogenic acid(29.16±1.02, 9.76±0.8 mg/g) and vanillic acid(59.32±1.01, 17.89±1.01 mg/g).6. DPPH?、ABTS+? scavenging capacity of mangosteen EP equaled 59.522, 101.396 mmol TE/100 g, respectively. The capacity of PA-A and PA-B equaled: 2.487, 3.094 mmol TE/100g(by DPPH assay) and 28.211, 6.364 mg TE/100g(by ABTS assay).