Biomedical Engineering Reference
In-Depth Information
HYDROCOLLOID
CH OH
2
OH
O
O
HO
O
O
HO
O
OH
ψ
φ
CH OH
2
PEPTIDE
O
R
H
H
φ
ψ
C
C
N
C
N
C
C
H
R
H
O
H
R
FIGURE 7.10
Structure of a typical hydrocolloid emphasizing its rigidity in comparison
to the structure of the flexible proteins with the ability to rotate.
H
YDROCOLLOIDS
Most hydrocolloids are polysaccharides with high water solubility and significant
structural rigidity; therefore, most investigators consider hydrocolloids as gelling
agents or viscosity builders (
Figure 7.10
).
The ability of polysaccharide hydrocol-
loids to stabilize colloidal dispersions and emulsions is usually explained in terms of
a modification of the structure and rheological properties of the aqueous continuous
phase.
179
Due to their predominantly hydrophillic character, most polysaccharides
have low surface activity at air-water or oil-water interfaces, and therefore are not
expected to form adsorbed layers in food colloids, which also contain proteins and
low-molecular weight surfactants. However, at least three groups of hydrocolloids
are well known to stabilize oil-in-water emulsions:
1.Gum arabic
2.Extracellular microbial “emulsan”
3.Chemically modified (containing auxillary groups such as methyl, ethyl,
acetyl, etc.) hydrocolloids such as pectin and cellulose
Recently,
180,181
work was done on other untreated hydrocolloids, such as galac-
tomannans (guar, LBG, fenugreek), and noticeable surface-activity was recorded for
some of these gums even after removal of most of the contaminating proteinaceous
material. Surface activity at the air-water interface was reported with solutions of
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