Chemistry Reference
In-Depth Information
1.0
0.8
0.6
0.4
0.2
0.0
5
6
7
8
9
log M
Figure 6 Adsorbed ratio c
ads
/c
whole emulsion
versus logarithm of the OSA-starch molar
mass
(Redrawn from Ref. 25.)
phase, and in the upper phase. The concentration in each molar mass class
could then be determined from mass balances using a maximum likelihood
estimation.
26
This procedure enables us to plot the adsorbed ratio (adsorbed
concentration divided by concentration in the whole emulsion) for each molar
mass class, as shown in Figure 6. The plot shows that the adsorbed ratio
increases with increasing molar mass, and approaches unity for the largest
molecules, while for a molar mass of
10
5
10
6
g mol
1
the ratio is only
0.5
0.65. Thus, it is clear that there is a preferential adsorption of the ultra-
high molar mass components during emulsification.
B
30.3.3 Protein Adsorption
The adsorption of the protein fraction at pH 7.0 was found to show a typical
Langmuir-type behaviour with a plateau value of
1.5 mg m
2
, as would be
expected for a water-soluble protein fraction adsorbing at a hydrophobic
interface.
27
A clear preferential adsorption of the components corresponding
to two of the dominant protein bands was observed when the interfacial area
was insufficient to accommodate all the available protein. These bands were
identified as serum albumin (protein 3) and yolk plasma glycoprotein YGP40
(protein 5).
28
For experiments in which protein concentration was kept constant and pH
was varied, significant degradation of some of the protein was observed below
pH 4 (Figure 7), which made it difficult to determine the selective adsorption
below this pH. Serum albumin seems to adsorb much more efficiently at pH
B
B
4
5, which is slightly below its pI. The glycoprotein YGP40 adsorbs efficiently
at any pH, with a slight increase in adsorbed amount at pH
6
8, which is
just above its pI. The component IgG adsorbs slightly more at pH 8, which is
close to its pI.
B
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