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Physicochemical, Structural and Conformational Properties of Heteropolysaccharides from Seeds of Artemisia Sphaerocephala Krasch

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Title: Physicochemical, Structural and Conformational Properties of Heteropolysaccharides from Seeds of Artemisia Sphaerocephala Krasch
Author: Guo, Qingbin
Department: Department of Food Science
Program: Food Science
Advisor: Yada, Rickey
Abstract: Artemisia Sphaerocephala Krasch (ASK) polysaccharide, extracted from the outer layer of ASK seeds, it has attracted attention due to its reported bioactivities. In the present study, extraction and fractionation methods for ASKP were developed. Two different Mw fractions 60P (MW: 551 KDa) and 60S (MW: 39 KDa) were obtained using ammonium sulphate precipitation. The physicochemical properties, in terms of rheological properties, chemical compositions and surface activities, of both fractions were elucidated. Using high performance anion exchange chromatography (HPAEC), partial acid hydrolysis, methylation analysis, 1D & 2D NMR spectroscopy and MALDI-TOF-MS methods, the detailed structural features of 60P and 60S were obtained, which were confirmed to be arabino(glucurono)xylan and (galacto)glucomannan, respectively Using light scattering and HPSEC techniques, the conformational properties of 60P were investigated. 0.5 M NaOH solution exhibited better ability to eliminate aggregates of 60P compared to water, NaCl solution and urea solution. The molecule of 60P exhibited a random coil conformation and semi-flexible structure in 0.5 M NaOH solution. In addition, the dependence of conformation of 60P on the molecular weight was also revealed by HPSEC analysis. The computer modeling technique using RIS-Metropolis Monte Carlo (RMMC) method was also applied. The conformational properties of 60P with different T-GlcpA ratio and various distribution patterns (random, alternative and block) along the xylan chain were determined. Results indicated that: the more regular the side chain distribution, the more extended the structure. The conformational properties of 60S with different molecular weights and various ratios of O-acetyl group to mannose were also considered. Results indicated that the radius of gyration (Rg) demonstrated an increasing trend with Mw and the data was comparable with that obtained from HPSEC; the insertion of O-acetyl group increased the chain extension at low ratio while showing a decrease it at a high ratio. The present study provides fundamental information regarding the physicochemical properties, structural and conformational properties of polysaccharides from the seeds of Artemisia sphaerocephala Krasch (ASK). Such information is essential to the understanding of the structure-conformation- functionality relationships of ASKP, thus promotes their potential food and industry applications.
Date: 2013-01

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