Enzymatic depolymerization of gum tragacanth: bifidogenic potential of low molecular weight oligosaccharides.
Gum tragacanth derived from the plant "goat's horn" (Astragalus sp.) has a long history of use as a stabilizing, viscosity-enhancing agent in food emulsions. The gum contains pectinaceous arabinogalactans and fucose-substituted xylogalacturonans. In this work, gum tragacanth from  Astragalus gossypinus  was enzymatically depolymerized using  Aspergillus niger  pectinases (Pectinex BE Color). The enzymatically degraded products were divided into three molecular weight fractions via membrane separation: HAG1 < 2 kDa; 2 kDa < HAG2 < 10 kDa; HAG3 > 10 kDa. Compositional and linkage analyses showed that these three fractions also varied with respect to composition and structural elements: HAG1 and HAG2 were enriched in arabinose, galactose, and galacturonic acid, but low in fucose and xylose, whereas HAG3 was high in (terminal) xylose, fucose, and 1,4-bonded galacturonic acid, but low in arabinose and galactose content. The growth-stimulating potential of the three enzymatically produced gum tragacanth fractions was evaluated via growth assessment on seven different probiotic strains in single-culture fermentations on  Bifidobacterium longum  subsp. longum (two strains), B. longum subsp. infantis (three strains),  Lactobacillus acidophilus , B. lactis, and on one pathogenic strain of  Clostridium perfringens . The fractions HAG1 and HAG2 consistently promoted higher growth of the probiotic strains than HAG3, especially of the three B. longum subsp. infantis strains, and the growth promotion on HAG1 and HAG2 was better than that on galactan (control). HAG3 completely inhibited the growth of the C. perfringens strain. Tragacanth gum is thus a potential source of prebiotic carbohydrates that exert no viscosity effects and which may find use as natural functional food ingredients.
Center for Bioprocess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark (DTU), DK-2800 Kgs. Lyngby, Denmark.
Hassan Ahmadi
HA
Gavlighi
Malwina
M
Michalak
Anne S
AS
Meyer
J Dalgaard
JD
Mikkelsen
D001234:Aspergillus niger / Q000201:enzymology*; D027883:Astragalus Plant / Q000737:chemistry*; D001644:Bifidobacterium / Q000187:drug effects / Q000254:growth & development; D005656:Fungal Proteins / Q000737:chemistry*; D008970:Molecular Weight; D009844:Oligosaccharides / Q000737:chemistry* / Q000494:pharmacology; D010936:Plant Extracts / Q000737:chemistry* / Q000494:pharmacology; D011096:Polygalacturonase / Q000737:chemistry*; D056692:Prebiotics / Q000032:analysis*; D014144:Tragacanth / Q000737:chemistry* / Q000494:pharmacology
D005656:Fungal Proteins; D009844:Oligosaccharides; D010936:Plant Extracts; D056692:Prebiotics; D014144:Tragacanth; D011096:Polygalacturonase