HASSAN AHMADI GAVLIGHI^1,2*, ANNE S. MEYER¹*, J. DALGAARD MIKKELSEN¹
*Corresponding authors
1. Technical University of Denmark (DTU),Center for Bioprocess Engineering, Department of Chemical and Biochemical Engineering, DK-2800, Kgs. Lyngby, Denmark
2. Tarbiat Modares University, Faculty of Agriculture, Department of Food Science
and Technology, P. O. Box 14115-336, Tehran, Iran

Abstract

Tragacanth gum is a plant derived hydrocolloid that has a long history of use in food, pharma, and cosmetics. The gum is mainly produced in the Middle East and permitted for food use in the US and Europe. Tragacanth gum consists of complex, heterogeneous polysaccharides, which contain different highly substituted pectin-like structural elements. Enzymatically produced low molecular- weight fractions of tragacanth gum exhibit potential prebiotic activity by promoting growth in vitro of Bifidobacterium longum subsp. infantis strains. These findings may lead to new uses of this gum for production of value-added prebiotic compounds for functional foods.

INTRODUCTION

Tragacanth gum is a natural plant exudate that is obtained from the stem of the bush like plant “goat’s-horn”, Astragalus species. The gum is used as a viscosity enhancer and stabilizer in emulsions and is permitted for food use in both the US and in Europe. Tragacanth gum is made up of highly substituted, heterogeneous hydrophilic polysaccharides that contain L-arabinose, D-galactose, D-glucose, D-xylose, L-fucose, L-rhamnose, and D-galacturonic acid (1, 2).
Tragacanthin is the water-soluble fraction, that confers high viscosity when suspended in water, and bassorin is the insoluble part which swells in water to form a gel (1). The gum saccharides form complexes with salts, notably salts with divalent cations, such as Ca2+ salts (3). Tragacanthin appears to resemble pectin, and contains linear chains of galacturonic acid (probably 1,4-α-linked) rich in xylose and with varying levels of fucose. The fucose levels depend on the plant species from which the gum is obtained (4). Tragacanth gum rich in xylose and galacturonic acid thus contains xylogalacturonan, whereas gum samples having high fucose, xylose, and galacturonic acid ...