Optimal Extraction And Structural Characterization Of Polysaccharides From Tamarindus Indica L. Pulp

Tamarindus indica L.is mainly distributed in Yunnan,Guangdong and other province in China.Pulp from Tamarindus indica L.was edible and rich in nutrients,which could be used as food ingredient.Studies showed that PTP had many functional properties,such as antioxidation.In this study,therefore,the pulp of Tamarindus indica L.was selected as raw material,of which the PTP was investigated with regard to its optimal extraction,fractionation,purification,physicochemical properties as well as characterization of fine structure.The main conclusions were shown as follows:(1)The optimum parameters for ultrasonic extraction of PTP were:50~oC extraction temperature,200 W ultrasonic power,30:1(mL/g)ratio of water to material,and 40 min extraction time.Under this optimized condition,the maxium extraction yield of PTP was 31.94%(w/w),which was significantly higher than that by hot water extraction(23.44%,w/w,p<0.05).The results of FT-IR spectroscopy showed that the hot water extraction could disrupt the carboxyl group and main chain of PTP to a relatively large degree,and reduce the degree of methyl esterification of PTP.(2)The results of chemical composition analysis showed that,after preliminary purification of PTP,the polysaccharide content in PTP was74.23%(w/w).The results of high-performance anion-exchange chromatography(HPAEC)manifested that PTP was mainly composed of arabinose(Ara),glucose(Glc),rhamnose(Rha),fucose(Fuc),galacturonic acid(GalA)and glucuronic acid(GlcA),with a molar ratio of57.49:21.28:8.32:1.76:9.03:2.12.According to the results of high-performance size-exclusion chromatography(HPSEC),PTP may consist of two components,and the average value of weight-average relative molecular weight(???_?_?)of PTP was 7.23×10~6 Da and 0.83×10~6 Da respectively with a non-uniform distribution.Cetyltrimethylammonium bromide(CTAB)was used to obtain neutral parts of PTP(nPTP)and acidic parts of PTP(aPTP),and the nPTP with a higher yield(72.13%,w/w)was fractionated into F25,F40,F55 and F70 via ethanol precipitation,and F55has the highest yield(61.08%,w/w)among them.(3)The basic chemical compositions of each component of PTP,i.e.,neutral PTP,acidic PTP,F25,F40,F55 and F70,were tested,and their molecular structure characteristics were analyzed comprehensively by UV spectroscopy,FT-IR spectroscopy,HPAEC and HPSEC,prior to further characterization of fine structure for F55 via methylation and NMR analyses.The results showed that there were differences among those components in terms of chemical compositions,monosaccharide compositions and relative molecular weights,besides,all components had characteristic absorption peaks of polysaccharide and pyranosyl structrures,while no nucleic acids were detected.With respect to F55,the???_?_?was 2.19×10~5 Da,and the polydispersity index(PDI)was 1.45.Moreover,F55 was mainly composed of Fuc,Rha,Ara,Gal,Glc and glucuronic acid(GlcA),with a molar ratio of3.38:4.17:39.19:0.73:50.48:2.05.Methylation and NMR analyses revealed that F55 has a relatively high degree of branching,with a 1,3-?-D-Glcp backbone ramified at O-4 or O-6.