2009_Book_FoodChemistry

4.4 Polysaccharides 313
contain a water-soluble arabinogalactan of
5–35% of the dry weight of the wood. It can be
isolated from chipped wood by a counter-current
extraction process, using water or dilute acids.
The extract is then usually drum dried.
4.4.4.12.2 Structure, Properties
Fig. 4.24. Gel strength of (a) tamarind flour and
(b) pectin from lemons versus saccharose concentration
(according to Whistler, 1973)
4.4.4.11.3 Utilization
The tamarind seed polysaccharide is a suitable
substitute for pectin in the production of marmalades
and jellies. It can be used as a thickening
agent and stabilizer in ice cream and mayonnaise
production.
4.4.4.12 Arabinogalactan from Larch
4.4.4.12.1 Occurrence, Isolation
Coniferous larch-related woods (Larix species;
similar to pine, but shed their needle-like leaves)
The polysaccharide consists of straight chain
β-D-galactopyranosyl units joined by 1 → 3
linkages and, in part, has side chains of galactose
and arabinose residues bound to positions 4
and 6. The suggested structure is given in
Formula 4.146.
In general, the polysaccharide is highly branched.
The molecular weight is 50–70 kdal. The
molecule is nearly spherical in shape, so its
aqueous solution behaves like a Newtonian fluid.
The viscosity is exceptionally low. At a temperature
of 20 ◦ C, the viscosity of a 10% solution
is 1.74 cps, a 30% solution 7.8 cps at pH 4 or
8.15 cps at pH 11, and a 40% solution 23.5cps.
These data show that the viscosity is practically
unaffected by pH. The solution acquires
a thick paste consistency only at concentrations
exceeding 60%.
4.4.4.12.3 Utilization
Arabinogalactan, due to its good solubility and
low viscosity, is used as an emulsifier and stabilizer,
and as a carrier substance in essential oils,
aroma formulations, and sweeteners.
(4.145)
(4.146)