Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
TABLE 15.3
Indicative Viscosities of Gum Solutions
Gum Conc.(%)
Apparent Viscosity
(cps) Reference
Arabic 1 50 2
Karaya 0.5 250 2
Gum ghatti 5 288 2
Tragacanth 1 3500 1
Arabinoxylan 1 3000 2
Larch arabinogalactan 10 2 2
Guar gum 1 4800 38
Locust bean gum 1 2000 32
Tara gum 1 3000 39
Glucomananan, konjac 1 30,000 49
Flaxseed gum 1 600 13
Psyllium gum 0.5 300 2
Tamarind gum 1 200 62
Quince seed gum 1 4000 2
Alginate 1 500 2
Alginate 2 5000 2
Agar 1.5 4a 98
Carrageenan kappa 1 300a 49
Furcelluran 1.5 80a 2
Note: Values for neutral pH, room temperature, and moderate shear (20 rpm).
a Values for hot viscosity at 60°C.
to the very large size and insolubility of the molecule. Cell walls also contain a large
variety of other polysaccharides of different sizes, composition, and solubility, many
of which can act as hydrocolloids. In the plant, these noncellulosic wall components
provide essential structural support for the wall. The more water-soluble polysaccharides
can be extracted from the wall and readily purified.
15.2.1 β-GLUCANS
β-glucans are a class of wall polysaccharides found in cereal grains, with a linear
chain of glucose residues joined by β(1-3) and β(1-4) linkages. β-Glucans are
typically obtained by alkaline hot-water extraction of oat and barley, which can
remove about 50% of the glucans present. Higher yields can be obtained by more
complicated processes for both oats 11 and barley. 12 β-glucans have a linear chain
with stretches of (1-3) linkages involving three or four glucose residues interspersed
with stretches of three or four (1-4)-linked glucose. β-glucans are generally coldwater
soluble, though some insoluble fractions might be present. Solutions have
moderate viscosity and show pseudoplastic behavior. Presence of some low-molecular-weight
fractions in β-glucan samples can give rise to unusual rheology. 13
β-Glucans at a 6% concentration can form gels after storage at low temperature.
Junction zones can form from the parallel alignment of cellulose-like stretches of