Characterisation of arabinogalactan from larch

Larch arabinogalactan (LAG) is a polysaccharide obtained from the wood of larch tree (Larix species). LAG is approved by the U.S. Food and Drug Administration (FDA) as a source of dietary fiber [1], but also has potential therapeutic benefits as an immune stimulating agent [2]. Our research tends to structural analysis of LAG as the main component of FiberAid™. Elementary analysis of LAG has shown that carbon and hydrogen atoms can be found in a 1: 2 molar ratio. No nitrogen or sulphur atoms could be detected, which indicates that LAG is not attached to a protein moiety. Quantification of neutral sugars by acetylation pointed out a 1: 5.8 ratio of arabinose (Ara) to galactose (Gal) as main monosaccharides. Determination of uronic acids by specific reduction with deuterium-labelling (NaBD₄) revealed small amounts of glucuronic acid (GlcA). Linkage type analysis by methylation showed that the main components are 1,3,6-Gal(p) and 1,6-Gal(p), as well as there being minor amounts of 1,3-Gal(p), 1,3-Ara(f) and terminal Ara(f), Ara(p), Gal(p) and GlcA(p). We were able to prove this by ¹³C-NMR spectroscopy data, which led to the following structural proposal:

Fig.1: Structural proposal for LAG

Acknowledgements: We thank Lonza Ltd., Visp (CH) for financial support of this work.

References: 1. Robinson R et al. (2001)J Am Coll Nutr 20: 179–285.

2. D'Adamo P (1996)J Naturopath Med 4: 32–39.