2009_Book_FoodChemistry

332 4 Carbohydrates
as a side chain on every third sugar residue (cf.
Formula 4.163).
On an average, 95% of the glucose residues are
present in the main chain. Dextran is very soluble
in water.
(4.163)
The polysaccharide has a molecular weight of
about 130 kdal and is very soluble in water. Solutions
have high viscosities and exhibit pseudoplastic
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 applied
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 of α-1,6-glucan: D-fructose-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 M r = 4−5 × 10 7 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)
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 Inulin and Oligofructose
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 furanoid D-fructose units
in a β-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 yields D-fructose on
acid or enzymatic hydrolysis. Oligofructans have
a slightly sweet taste due to the lower degree of
polymerization.