332 4 Carbohydrates
as a side chain on every third sugar residue (cf.
Formula 4.163).
(4.163)The polysaccharide has a molecular weight of
about 130 kdal and is very soluble in water. So-
lutions have high viscosities and exhibit pseudo-
plastic thixotropic properties.
4.4.4.20.3 Utilization
Scleroglucan is used as a food thickener and, on
the basis of its good film-forming property, is ap-
plied as a protective coating to dried foods.
4.4.4.21 Dextran................................................
4.4.4.21.1 Occurrence.............................................
Leuconostoc mesenteroides, Streptobacterium
dextranicum, Streptococcus mutans and some
other bacteria produce extracellular dextran from
saccharose with the help ofα-1,6-glucan:D-fruc-
tose-2-glucosyl transferase (dextran sucrase, EC
2.4.1.5).
4.4.4.21.2 Structure,Properties.....................................
Dextran is an α-1,6-glucan (Formula 4.164;
molecular weight Mr= 4 − 5 × 107 dal) with
several glucose side chains, which are bound to
the main chain of the macromolecule primarily
through 1,3-linkages but, in part, also by 1,4- and
1,2-linkages.
(4.164)On an average, 95% of the glucose residues are
present in the main chain. Dextran is very soluble
in water.4.4.4.21.3 Utilization
Dextran is used mostly in medicine as a blood
substitute. In the food industry it is used as
a thickening and stabilizing agent, as exemplified
by its use in baking products, confections,
beverages and in the production of ice creams.4.4.4.22 InulinandOligofructose..................................
4.4.4.22.1 Occurrence.............................................
Inulin occurs as a reserve carbohydrate in many
plant families, e. g., scorzonera, topinambur,
chicory, rye, onion and dahlia bulb.4.4.4.22.2 Structure...............................................
Inulin contains about 30 furanoidD-fructose units
in aβ-1,2-linkage. This linear polysaccharide has
α-glucose residues in 2,1-bonding at its ends.
Individual α-glucose residues in 1,3-bonding
have also been detected in the interior of the
polysaccharide. Inulin(M, 5000–6000) is soluble
in warm water and resistant to alkali.4.4.4.22.3 Utilization
Inulin is nondigestible in the small intestine, but
is degraded by the bacteria in the large intestine.
It can be used in many foods as a sugar and fat
substitute (cf. 8.16.1.2), e. g., biscuits, yoghurt,
desserts and sweets. Inulin yieldsD-fructose on
acid or enzymatic hydrolysis. Oligofructans have
a slightly sweet taste due to the lower degree of
polymerization.