Biomedical Engineering Reference
In-Depth Information
mN/m
70
60
50
40
30
0.05
0.2
0.5
1
25 10
20
Concentration (%)
FIGURE 7.11 Plot of the surface tension vs. the concentration of the hydrocolloid.
( ) Dextrin; (X) κ-carrageenan; ( ) gum arabic; ( ) guar gum (diluted 1:20). (From Reichman,
D., Ph.D. thesis, Hebrew University of Jerusalem, Israel, 1990. With permission.)
other gums as well ( Figure 7.11 ). For example, a 1 wt% solution of xanthan gum 182
and a 0.1 wt% solutions of gum tragacanth or sugar beet acetylated pectin. 183
Gum Arabic
In terms of the properties of its adsorbed films, the most widely studied hydrocolloid
(after gelatin) is gum arabic. It is a highly complex branched polysaccharide
carboxylic acid (ca. 2.5
10 5 Da) occurring naturally in the form of its potassium,
magnesium, and calcium salts. The surface activity of arabic acid and its salts (also
called gum acacia), and their ability to form thick viscoelastic films at oil-water
interfaces, was demonstrated almost 30 years ago. 184 Subsequently, Nakamura
et al. 185,186 studied the dependence on molecular weight of the surface rheology of
gum arabic films at coconut oil-water interface and observed a correlation between
surface viscosity and emulsion stability. The values of the surface modulus and
surface viscosity for 24-h-old films adsorbed on the oil-water interface (pH 7, 30°C)
from solutions at various samples of commercial gum arabic. 186 The data clearly
showed that the rheological parameters are increasing functions of the weight-
average molecular weight, whereas interfacial tension under the same experimental
conditions was essentially independent of molecular weight.
The pioneering work by Anderson 187 over the past 20 years showed that gum
arabic, in common with other gums (sugar, tragacanth, xanthan, etc.), contained a
low level of nitrogen which was attributed to bound protein (or polypeptide). If a
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