arabinogalactan

Arabinogalactan is a polysaccharide composed primarily of arabinose and galactose residues. It occurs in plants as a structural component of the cell wall and as part of glycoproteins known as arabinogalactan proteins. In plants, arabinogalactan exists in two major contexts: as complex side chains of pectic and RG-I polysaccharides within the cell wall, and as covalently attached carbohydrate chains on arabinogalactan proteins, where a protein core is decorated with extensive type II arabinogalactan chains rich in galactose and arabinose.

Natural sources and extraction: Arabinogalactan is widely distributed across vascular plants. A major purified form is larch arabinogalactan, derived from the heartwood of Larix species, yielding a high molecular weight, water-soluble polymer. Gum arabic from Acacia species also contains substantial arabinogalactan as part of its composition and is another common natural source.

Structure and diversity: The cell-wall-associated arabinogalactan comprises galactose-rich backbones with arabinose-containing side chains, whereas arabinogalactan proteins carry extensive type II arabinogalactan oligosaccharides that are heavily galactose- and arabinose-rich attached to a protein core. The exact structure can vary by species and tissue.

Uses and properties: Arabinogalactan is used as a source of dietary fiber and as a food additive and thickener. It is generally water-soluble and resistant to digestion in the upper gastrointestinal tract, with fermentation by gut bacteria that has been studied for potential prebiotic effects.

Safety and regulation: It is commonly used in foods and supplements and is regarded as safe when consumed within typical dietary amounts.