Structural characterization of a low-molecular-weight heteropolysaccharide (glucomannan) isolated from Artemisia sphaerocephala Krasch Qingbin Guo a,b , Steve W. Cui a,b,⇑ , Qi Wang b , Xinzhong Hu c , Ji Kang b , Rickey Y. Yada a a Department of Food Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1 b Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, Ontario, Canada N1G 5C9 c College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China article info Article history: Received 15 August 2011 Received in revised form 7 October 2011 Accepted 12 October 2011 Available online 18 October 2011 Keywords: Artemisia sphaerocephala Krasch NMR Partial acid hydrolysis Methylation analysis MALDI-TOF-MS Polysaccharides abstract Using 60% (w/v) ammonium sulfate precipitation, a heteropolysaccharide (designated 60S), with rela- tively low molecular weight (38.7 kDa), was isolated from the seeds of Artemisia sphaerocephala Krasch. The structural properties of 60S were elucidated by partial acid hydrolysis, methylation analysis, 1D and 2D NMR spectroscopy, and MALDI-TOF-MS. The results of the partial acid hydrolysis and methylation analysis indicated that the main chain of 60S consisted of (1?4)-linked D-Manp and (1?4)-linked D-Glcp in a molar ratio of 1:1.3. Over half of the glucosyl residues in the main chain were branched at the O-6 position. The terminal sugar residues were mainly composed of T-Araf, T-Arap, T-Galp, T-GlcpA, and T- Glcp. Besides, 3-Araf and 2-Galp were also observed in comparable amounts. Based on all the aforemen- tioned results and the data obtained by 1D and 2D NMR spectroscopy as well as MALDI-TOF-MS, a struc- ture of 60S is proposed as follows: R could be one or some of -(3-a-Araf) n -(A), T-a-Galp (B), T-a-Glcp (C), T-Araf (H) or T-Arap. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. 1. Introduction A crude water-extractable polysaccharide from Artemisia sph- aerocephala Krasch (ASK) seed has been used in the food industry in China as a thickener, a water-holding agent, and a stabilizer since the 1980s. Recent reports showed that the crude polysaccha- ride from ASK was able to alleviate hyperglycemia, hyperlipemia, and insulin resistance in streptozotocin-induced type 2 diabetic rats, 1 and the polysaccharide showed significant antioxidant effects on diabetic rats. 2 It was also reported that the ASK polysac- charide could decrease the blood glucose levels in alloxan-induced type 1 diabetic rats. 3 However, limited information on the structural properties of the ASK polysaccharide is available. In our previous study, 4 two polysaccharide fractions were iso- lated from the water-extractable ASK polysaccharide using 60% (w/v) ammonium sulfate precipitation. The higher molecular weight polysaccharide (551.3 kDa) was collected from the precipi- tate and designated 60P, while the fraction with relatively low molecular weight (38.7 kDa) was recovered from the supernatant and named as 60S. Substantial differences were observed between 60P and 60S in terms of physicochemical properties: 60P was com- prised of 55.4% (w/w) neutral sugar, 25.8% (w/w) uronic acid, and 24.1% (w/w) protein, while in 60S, the percentage of neutral sugar and uronic acid was 87.1% (w/w) and 10.4% (w/w), respectively, with no protein detected. In addition, monosaccharide composition analysis showed that 60S was composed of 38.3% (w/w) glucose, 28.1% (w/w) mannose, 24.2% (w/w) galactose, 9.4% (w/w) arabi- nose, and a trace amount of rhamnose. The proposed structure of 60P was reported previously: it has a (1?4)-linked xylopyranose backbone branched at every other xylopyranose at the O-2 position with mostly T-a-GlcpA-4?OMe, and occasionally 4-a-D-GalpA, T- Araf, T-Arap or 3-b-Araf. 5 The objective of the current study was to elucidate the fine structure of 60S, employing partial acid hydrolysis, methylation analysis, MALDI-TOF-MS, and 1D and 2D NMR spectroscopy 0008-6215/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.carres.2011.10.020 ⇑ Corresponding author. Tel.: +1 519 780 8028; fax: +1 519 829 2600. E-mail address: cuis@agr.gc.ca (S.W. Cui). Carbohydrate Research 350 (2012) 31–39 Contents lists available at SciVerse ScienceDirect Carbohydrate Research journal homepage: www.elsevier.com/locate/carres